Journal articles: 'Variable-range hopping model'

1

Wilkinson, M., B. Mehlig, and V. Bezuglyy. "Stick-breaking model for variable-range hopping." Philosophical Magazine Letters 88, no. 5 (May 2008): 327–34. http://dx.doi.org/10.1080/09500830801971462.

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Huda, Abdullah. "Variable Range Hopping (VRH) Model in Manganese Oxides." Defect and Diffusion Forum 303-304 (July 2010): 117–23. http://dx.doi.org/10.4028/www.scientific.net/ddf.303-304.117.

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This is a study of data analyzing by using a theoretical model for mixed-valence manganites Ln1−xAxMnO3, which exhibit a complex transport behaviour. In the high-temperature (T>TP) paramagnetic insulating regime, the resistivity of samples obeys the T-1/4 law, characteristic of variable range hopping (VRH). We address this kind of transport process as involving variable-range hopping of small polarons, and derive the resistivity expression: .

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Mehlig, Bernhard, and Michael Wilkinson. "Precise Asymptotics for a Variable-Range Hopping Model." Progress of Theoretical Physics Supplement 166 (2007): 136–42. http://dx.doi.org/10.1143/ptps.166.136.

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Hohl, H., and E. Bucher. "Pr1.9Sr1.1Cu2O6: A model 2D variable range hopping conductor." Solid State Communications 97, no. 9 (March 1996): 747–50. http://dx.doi.org/10.1016/0038-1098(95)00759-8.

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Bozhko, A. D., S. V. Demishev, V. V. Glushkov, E. A. Kataeva, N. E. Sluchanko, and A. G. Lyapin. "Spin-Dependent Variable Range Hopping Conductivity." Solid State Phenomena 152-153 (April 2009): 545–48. http://dx.doi.org/10.4028/www.scientific.net/ssp.152-153.545.

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Basing on the study of the transport in disordered carbon nanomaterials we argue that the correct description of the magnetoresistance can be obtained in a spin polarization theory, which processes separately the spin and orbital degrees of freedom in hoping conductivity in magnetic field. It is found that the polarization of the spin part of the electron wave function controls the probabilities of the hops between the single and double occupied localized states and, moreover, the spin polarization process can be treated as in the paramagnet with spin S=1/2. The experimental checking of the universal magnetoresistance scaling expected in the spin polarization model is provided.

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BHATIA, S. N., and R. WALIA. "VARIABLE RANGE HOPPING IN OXYGEN DEFICIENT YBa2Cu3Ox." International Journal of Modern Physics B 02, no. 06 (December 1988): 1381–86. http://dx.doi.org/10.1142/s0217979288001190.

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Our measurement of the resistivity and thermoelectric power from 20–300 K in the oxygen deficient YBa 2 Cu 3 O x annealed at 700, 800 and 850°C show good agreement with Mott's variable range hopping model below ~ 100 K.

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Khan, Zishan Husain, Numan Salah, and Sami Habib. "Electrical Transport Properties ofNi95Ti5Catalyzed Multi wall Carbon Nanotubes Film." Journal of Nanomaterials 2009 (2009): 1–8. http://dx.doi.org/10.1155/2009/429867.

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Carbon nanotubes (CNTs) can be understood as one or more graphite sheets rolled up into a seamless cylinder. CNTs have gained much attention and scientific interest due to their unique properties and potential applications since their discovery in 1991. In the present work, we have deposited Ni95Ti5 film using thermal deposition method. Finally, theNi95Ti5catalyzed multi wall carbon nanotubes (MWNTs) are grown on silicon substrate using low pressure chemical vapor deposition (LPCVD) method and the electrical transport properties of this MWNTs film are studied over a temperature range (284–4K) to explain the conduction mechanism. We have suggested two types of conduction mechanism for the entire temperature range. For the temperature region (284–220K), the conduction is due to thermally activated process, whereas the conduction takes place via variable range hopping (VRH) for the temperature range of (220–4K). The VRH mechanism changes from three dimensions to two dimensions as we move down to the temperature below 50K. Therefore, the data for the temperature region (220–50K) is plotted for three dimensional variable range hopping (3D VRH) model and the two dimensional variable range hopping (2D VRH) for lower temperature range of (50–4K). These VRH models give a good fit to the experimental data. Using these models, we have calculated various interesting electrical parameters such as activation energy, density of states, hopping distance and hopping energy.

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RAMESH, K. V., N. MANJULA BHARATHI, B. SRINIVASA RAO, and P. APPALA NAIDU. "AN ADIABATIC HOPPING OF dc ELECTRICAL CONDUCTIVITY STUDIES ON NiO SUBSTITUTED LEAD VANADATE GLASSES." International Journal of Modern Physics B 23, no. 23 (September 20, 2009): 4833–41. http://dx.doi.org/10.1142/s0217979209053023.

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Glasses of the system x ( NiO ) (50 – x) PbO : 50V 2 O 5 were prepared by melt quenching in the range x = 0 mol % to 15 mol%. Measurements are reported for dc electrical conductivity for the above compositions in the temperature range 300 K–500 K. The experimental results are analyzed with reference to various theoretical models proposed for dc electrical conduction in amorphous semiconductors. The analysis shows that at high temperatures the temperature dependence of dc conductivity is consistent with Mott's model of phonon-assisted hopping conduction, variable range hopping mechanism and Schnakenberg's model mechanism. The hopping in this system is adiabatic in nature.

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Grimaldi, C., P. Ryser, and S. Strässler. "Gauge factor of thick-film resistors: Outcomes of the variable-range-hopping model." Journal of Applied Physics 88, no. 7 (2000): 4164. http://dx.doi.org/10.1063/1.1290738.

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SHILAN, S. T., L. S. EWE, and R. ABD-SHUKOR. "ELECTRICAL AND MAGNETO-TRANSPORT PROPERTIES OF La0.8Sr0.2MnO3." International Journal of Modern Physics B 25, no. 28 (November 10, 2011): 3825–33. http://dx.doi.org/10.1142/s0217979211102095.

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The effects of sintering temperature on the electrical and magneto-transport properties of La 0.8 Sr 0.2 MnO 3 compounds prepared by employing a chemical co-precipitation route sintered at 1120°C, 1220°C and 1320°C are reported. The X-ray powder diffraction patterns for all samples can be indexed to the rhombohedra structure with R3C space group. The insulator–metal transition temperature remained nearly constant (~291 K) for all samples. The magneto resistance (MR) values were found to decrease noticeably as the sintering temperature was increased from 1120°C to 1320°C. Above 0.3 T, the magneto resistance was influenced by To values, which indicates the bending of Mn–O–Mn bond. The resistivity data were fitted with several equations in the metallic (ferromagnetic) region. In the insulating (paramagnetic) region, the variable range hopping and small polaron hopping models were used to compute the density of states at the Fermi level, N(EF), and activation energy (Ea) of the electrons. The resistivities can be fitted well with ρ–T2 and ρ–T2.5 curves. The variable range hopping model and small polaron hopping model fitted very well at high temperature regions, indicating that small polaron hopping might be responsible for the conduction. La 0.8 Sr 0.2 MnO 3 sintered at 1220°C demonstrated the highest MR of 6.5% in 1 T magnetic field.

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RAMESH, K. V., and D. L. SASTRY. "DC ELECTRICAL PROPERTIES OF CuO SUBSTITUTED LEAD VANADATE GLASS SYSTEM." Modern Physics Letters B 20, no. 22 (September 30, 2006): 1357–66. http://dx.doi.org/10.1142/s0217984906011372.

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Glasses of the system x( CuO )(50-x) PbO :50 V 2 O 5 were prepared by melt quenching in the range x=0 mol % to 15 mol%. Measurements are reported for DC electrical conductivity for the above compositions in the temperature range 300–500 K. The experimental results are analyzed with reference to various theoretical models proposed for DC electrical conduction in amorphous semiconductors. The analysis shows that at high temperatures the temperature dependence of DC conductivity is consistent with Mott's model of phonon-assisted hopping conduction, variable range hopping mechanism and Schnakenberg's model mechanism. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation in these glasses.

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12

Lopes, V. C., A. J. Syllaios, D. Whitfield, K. Shrestha, and C. L. Littler. "1/f Noise in Mott Variable Range Hopping Conduction in p-type Amorphous Silicon." MRS Proceedings 1770 (2015): 25–30. http://dx.doi.org/10.1557/opl.2015.546.

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ABSTRACTWe report on electrical conductivity and noise measurements made on p-type hydrogenated amorphous silicon (a-Si:H) thin films prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD). The temperature dependent electrical conductivity can be described by the Mott Variable Range Hopping mechanism. The noise at temperatures lower than ∼ 400K is dominated by a 1/f component which follows the Hooge model and correlates with the Mott conductivity. At high temperatures there is an appreciable G-R noise component.

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BUSCEMI, FABRIZIO, ENRICO PICCININI, MASSIMO RUDAN, ROSSELLA BRUNETTI, and CARLO JACOBONI. "DIFFUSION AND HIGH-FREQUENCY NOISE OF ELECTRONS IN AMORPHOUS SEMICONDUCTORS AT LOW ELECTRIC FIELDS." Fluctuation and Noise Letters 11, no. 03 (September 2012): 1242004. http://dx.doi.org/10.1142/s0219477512420047.

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The Ohmic conduction, diffusion, and high-frequency noise in amorphous semiconductors are here investigated by means of a Monte Carlo implementation of a full three-dimensional variable-range hopping transport model between localized states. Quantities like the carrier-velocity autocorrelation function, the noise power spectrum, the diffusion coefficient and the ohmic conductivity are obtained from numerical simulations at room and lower temperatures. Some interesting features of the linear-response regime typical of hopping transport are observed and discussed.

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14

Sita, D. R., and R. Singh. "Thermo-Electric Power of the Bi2Sr2Ca1-xCexCu2Oy System." Modern Physics Letters B 12, no. 12 (May 20, 1998): 475–88. http://dx.doi.org/10.1142/s0217984998000585.

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The temperature dependence of thermo-electric power (TEP) of Bi 2 Sr 2 Ca 1-x Ce x Cu 2 O y samples with x upto 0.4 are reported in the temperature range 40–300 K. The normal state TEP data of the superconducting samples are discussed in view of some of the existing theoretical models in the literature, viz. two-band models, Nagaosa and Lee model and a phenomenological narrow band model. The transport in the semiconducting sample is found to be by variable-range-hopping mechanism.

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Łoś, Szymon, Kazimierz Fabisiak, Kazimierz Paprocki, Mirosław Szybowicz, and Anna Dychalska. "The Undoped Polycrystalline Diamond Film—Electrical Transport Properties." Sensors 21, no. 18 (September 12, 2021): 6113. http://dx.doi.org/10.3390/s21186113.

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The polycrystalline diamonds were synthesized on n-type single crystalline Si wafer by Hot Filament CVD method. The structural properties of the obtained diamond films were checked by X-ray diffraction and Raman spectroscopy. The conductivity of n-Si/p-diamond, sandwiched between two electrodes, was measured in the temperature range of 90–300 K in a closed cycle cryostat under vacuum. In the temperature range of (200–300 K), the experimental data of the conductivity were used to obtain the activation energies Ea which comes out to be in the range of 60–228 meV. In the low temperature region i.e., below 200 K, the conductivity increases very slowly with temperature, which indicates that the conduction occurs via Mott variable range hopping in the localized states near Fermi level. The densities of localized states in diamond films were calculated using Mott’s model and were found to be in the range of 9×1013 to 5×1014eV−1cm−3 depending on the diamond’s surface hydrogenation level. The Mott’s model allowed estimating primal parameters like average hopping range and hopping energy. It has been shown that the surface hydrogenation may play a crucial role in tuning transport properties.

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Shin, Dong Hwan, and Ji Nung An. "Effects of Torsional Stiffness and Preload on a Hopping Robot with Two-Segment Legs." Applied Mechanics and Materials 138-139 (November 2011): 153–58. http://dx.doi.org/10.4028/www.scientific.net/amm.138-139.153.

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In this study, we present the effects of design parameters on the performance of a hopping robot. In particular, we focus on the effects of torsional stiffness and preload on a hopping model with two-segment legs having passive knee joints with torsional stiffness. One of the objectives for a field robot is the ability to travel quickly with energy efficiency [1]. Therefore, it is important to determine what range of each design variable is proper to realize not only the high forward speed for great mobility, but also the low torque consumption for energy efficiency. Accordingly, we describe both the analogy simulation of a hopping gait with two-segment legs and the results of this simulation.

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17

Wang, Lin, Zhen Ping Wu, Yu Cheng Jiang, Bing Ren, Jian Huang, Lin Jun Wang, Yi Ben Xia, and Ju Gao. "Impact of the Oxygen Content on the Electronic Properties in Epitaxial Thin Films of Electron-Doped La_0.9Hf_0.1MnO₃." Advanced Materials Research 634-638 (January 2013): 2485–88. http://dx.doi.org/10.4028/www.scientific.net/amr.634-638.2485.

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Thin films of perovskite manganite La0.9Hf0.1MnO3 (LHMO) have been grown on (100) SrTiO3 single-crystal substrates with different growth pressures by pulsed laser deposition. The different transport behaviors of films have been fitted by various models. The results clearly demonstrate that oxygen pressure is an efficient way to change the transport behaviors of LHMO films. All the transport behaviors observed in LHMO films can be better fitted by Mott’s variable range hopping model than the other two models.

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Sarmah, Smritimala, and Ashok Kumar. "PAni-SnO₂Nanocomposite: Irradiation Induced Charge Transport Processes." Solid State Phenomena 209 (November 2013): 39–43. http://dx.doi.org/10.4028/www.scientific.net/ssp.209.39.

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The films of polyaniline–tin oxide (PAni–SnO2) nanocomposites were synthesized by chemical oxidative polymerization technique. These films were irradiated with 90 MeV O7+ ions at the fluences of 5×1010, 1×1011, 5×1011, and 1×1012 ions/cm2. X-ray diffraction studies show that microstrain and domain crystallite size of SnO2 nanoparticles in PAni matrix increase with the increase of ion fluence, resulting in highly ordered PAni–SnO2 nanocomposites. DC electrical conductivity is found to increase with the increase of fluence and conduction mechanism follows a quasi one-dimensional variable-range hopping model. AC electrical conductivity also increases with the increase of ion fluence and obeys correlated barrier-hopping model.

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Lindemuth, Jeffery, Alexander J. E. Rettie, Luke G. Marshall, Jianshi Zhou, and C. Buddie Mullins. "Electronic Transport Characterization of BiVO4 Using AC Field Hall Technique." MRS Proceedings 1633 (2014): 43–49. http://dx.doi.org/10.1557/opl.2014.270.

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ABSTRACTBismuth vanadate (BiVO4) is a photoelectrode for the oxidation of water. It is of fundamental importance to understand the electrical and photoelectrochemical properties of this material. In metal oxides, the electronic transport is described by the small polaron model, first described by Mott. In this model, the resistivity varies with temperature as $\rho \,\left( T \right)\, \propto \,Te^{({{E_a } \mathord{\left/ {\vphantom {{E_a } {(k_B T))}}} \right. \kern-\nulldelimiterspace} {(k_B T))}}} $, where Ea is the hopping activation energy, kB is the Boltzmann constant and T is the absolute temperature. Resistivity measurements confirm that small polaron hopping dominates in temperature ranges from 250 K to 300 K. In addition measurements from 175K to 250K show the variable range hopping dominates the transport. To this end, the electronic transport properties of BiVO4 single crystal were characterized using resistivity measurements and Hall effect measurements over temperatures ranging from 175 K to 300 K.

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Banaszak-Piechowska, Agnieszka, Kazimierz Fabisiak, Elżbieta Staryga, and Kazimierz Paprocki. "Electrical properties and Mott parameters of polycrystalline diamond films synthesized by HF CVD method from hydrogen/methanol gas mixture." Materials Science-Poland 35, no. 4 (March 20, 2018): 830–37. http://dx.doi.org/10.1515/msp-2017-0101.

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Abstract The influence of diamond crystallinity and preferred orientation on electronic conductivity of synthetic diamond films grown by hot filament chemical vapor deposition (HFCVD) was investigated. The CVD diamond films of different morphologies and crystallite sizes varying from 36 nm to 67 nm, measured in h2 2 0i direction were considered. The charge transport mechanism in the diamond samples was studied using temperature dependent DC conductivity measurements. The obtained results showed that in the temperature range of 90 K to 300 K charge transport is realized via Variable Range Hopping (VRH, m = 1/4) mechanism. Using VRH model, the Mott parameters were evaluated i.e. density of states at Fermi level N(EF) (0.22 × 1015 eV-1·cm-3 to 1.7 × 1015 eV-1·cm-3), hopping energy W (43.5 meV to 142.3 meV) and average hopping distance R (1.49 × 10-5cm to 2.56 × 10-5cm). It was shown that above mentioned parameters strongly depend on diamond film preferential orientation.

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Sundaray, Bibekananda, V. Jagadeesh Babu, V. Subramanian, and T. S. Natarajan. "Preparation and Characterization of Electrospun Fibers of Poly(methyl methacrylate) - Single Walled Carbon Nanotube Nanocomposites." Journal of Engineered Fibers and Fabrics 3, no. 4 (December 2008): 155892500800300. http://dx.doi.org/10.1177/155892500800300405.

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Electrospinning is a versatile method of preparing polymer nanocmposite fibers. Electrospun nanocomposite fibers of poly(methyl methacrylate) and single walled carbon nanotubes were prepared. The fibers were characterized by SEM, TEM, TGA and Raman spectroscopy. These fibers show dramatic improvement in the electrical conductivity compared to the polymer. The temperature dependent electrical resistance measurements show a one dimensional variable range hopping model (1–D VRH) type of conduction mechanism operating in these types of systems.

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22

Ali, A. I., and A. Hassen. "Magnetic and Electric Properties of , () Layered Perovskites." Advances in Condensed Matter Physics 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/714143.

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The electric and magnetic properties of layered perovskites have been investigated systematically over the doping range . It was found that both Sr1.5Y0.5CoO4and Sr1.4Y0.6CoO4undergo ferromagnetic (FM) transition around 145 K and 120 K, respectively. On the other hand, Sr1.3Y0.7CoO4and Sr1.2Y0.8CoO4compounds showed paramagnetic behavior over a wide range of temperatures. In addition, spin-glass transition () was observed at 10 K for Sr1.3Y0.7CoO4. All investigated samples are semiconducting-like within the temperature range of 10–300 K. The temperature dependence of the electrical resistivity, , was described by two-dimensional variable range hopping (2D-VRH) model at 50 K < ≤ 300 K. Comparison with other layered perovskites was discussed in this work.

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Ameer, Shahid, and Asghari Maqsood. "Electrical and Dielectric Spectroscopic Characterization of Polycrystalline Dy₂Si₂O₇." Key Engineering Materials 510-511 (May 2012): 194–200. http://dx.doi.org/10.4028/www.scientific.net/kem.510-511.194.

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The compound Dy2Si2O7exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy2Si2O7are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (To) and density of states at fermi level are obtained. The ac conductivity σac(ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σac(ω) =B ωs, where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

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Winarsih, Suci, Faisal Budiman, Hirofumi Tanaka, Tadashi Adachi, Takayuki Goto, Bambang Soegijono, Budhy Kurniawan, and Isao Watanabe. "Variable Range Hopping Resistivity in La_2-_xSr_xCuO₄ Nanoparticles Evaluated by Four Point Probe Method." Key Engineering Materials 860 (August 2020): 142–47. http://dx.doi.org/10.4028/www.scientific.net/kem.860.142.

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We report the results of the resistivity measurement on La2-xSrxCuO4 nanoparticles with x = 0, 0.05, and 0.20 evaluated by the four-point probe method. The high resistivity value shows the predominance of the inter-grain part. The temperature dependence of the conductivity can be analyzed by variable range hopping model showing the charge carriers are formed by thermal activation. There is no superconducting behavior that could be observed in La2-xSrxCuO4 nanoparticles with x = 0.05 and 0.20.

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APARECIDO-FERREIRA, A., E. S. ALVES, G. M. RIBEIRO, and J. F. SAMPAIO. "THE MAGNETORESISTANCE OF CARBON-BLACK SAMPLES AT DIFFERENT TEMPERATURES." International Journal of Modern Physics B 23, no. 12n13 (May 20, 2009): 2960–63. http://dx.doi.org/10.1142/s0217979209062621.

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We present experimental results for the magnetoresistance of carbon-black, in magnetic fields (B) up to 15 T, and its temperature dependence at temperatures (T) from 10 K to 1.2 K. At these temperatures the electrical conduction is given by variable range hopping with Coulomb gap. The results show a B2 dependence at low fields and a B1/2 dependence in the limits of high fields. We show that the model of hydrogenlike localized states cannot explain the experimental results.

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Tawansi, A., S. I. Badr, and M. Abdelaziz. "Crystallization and physical properties of polyvinyl acetate/polyvinylidene fluoride blends." Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 217, no. 1 (January 1, 2003): 57–63. http://dx.doi.org/10.1177/146442070321700107.

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Structural and thermal characterizations and dc resistivity measurements were performed for polyvinyl acetate (PVAc)/polyvinylidene fluoride (PVDF) blends. The ferro- to para- electric transition temperature ( TFP) and the melting temperature of PVDF were detected by DTA. X-ray diffraction and infrared analysis evidenced the presence of α- and β-PVDF crystalline phases for the studied blends. IR spectra revealed some structural defects such as difluorinated alkenes and head-to-head segments. The optical absorption spectra suggested the presence of two optical gaps. The electrical resistivity results were discussed on the basis of the modified interpolaron hopping model. The calculated values of the charge carrier hopping distance were in the range of 5.5-7.5 nm. The present blends are suggested to be used as pressure and microwave sensors and to produce a surface acoustic wave diffraction grating of variable order for laser optical communications.

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González-Campos, J. Betzabe, Evgen Prokhorov, Isaac C. Sanchez, J. Gabriel Luna-Bárcenas, Alejandro Manzano-Ramírez, Jesús González-Hernández, Yliana López-Castro, and Rosa E. del Río. "Molecular Dynamics Analysis of PVA-AgnPComposites by Dielectric Spectroscopy." Journal of Nanomaterials 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/925750.

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The molecular dynamics of PVA/AgnP composites were studied by dielectric spectroscopy (DS) in the 20–300°C temperature range. Improper water elimination leads to misinterpretation of thermal relaxations in PVA composites in agreement with the previous report for pristine PVA. The evaporation of water and its plasticizing effect are more evident in pure PVA confirming the existence of strong interaction between OH groups of PVA chains and AgnP. Dry films show a single nonlinear VFT dependence (from 45°C until melting) associated to theα-relaxation and, therefore, to the glass transition phenomenon and from dielectric measurements, theTgof composites vary from 88°C for pristine PVA to 125°C for PVA/AgnP (5 wt%). Below 45°C, dry films exhibit a single Arrhenius behavior showing a 3D hopping conductivity as explained based on the variable range hopping model. PVA/AgnP composites have higher conductivity compared to pristine PVA, and it increases as AgnP weight percent increases. Finally, DMA measurements support the statement that a secondary relaxation was erroneously assigned as the glass transition of PVA and composites in previous reports.

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THAKUR, RAJESH K., RASNA THAKUR, ANCHIT MODI, N. KAURAV, G. S. OKRAM, and N. K. GAUR. "ELECTRONIC TRANSPORT MECHANISM IN YMn0.8Ru0.2O3 COMPOUND." International Journal of Modern Physics: Conference Series 22 (January 2013): 626–29. http://dx.doi.org/10.1142/s2010194513010763.

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A single phase polycrystalline hexagonal YMn0.8Ru0.2O3 compound with space group P63cm (25-1079) have been synthesized by using solid state reaction method at sintering temperature 1280°C. The detailed low temperature electrical properties were evaluated over a broad range of temperature. The temperature dependence of the dc resistivity at low temperature reveals the semiconducting behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the ;temperature scale T* ~ 1.05 × 106 K and finally the density of state at Fermi level N(EF) is calculated to be ~ 5.6 × 1019 eV−1 cm−3.

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Sutar, Rani Ananda, Latha Kumari, and Murugendrappa M. V. "Investigation of temperature-dependent conduction mechanism in MnCo2O4/polypyrrole nanocomposites by three-dimensional variable range hopping (3D-VRH) and band-conduction model." Journal of Applied Physics 130, no. 1 (July 7, 2021): 015112. http://dx.doi.org/10.1063/5.0039671.

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Yang, He, Yun Ze Long, and Hang Jun Ding. "Template-Free Synthesis and Properties of Polyaniline Nanostructures Doped with Different Oxidants." Materials Science Forum 688 (June 2011): 334–38. http://dx.doi.org/10.4028/www.scientific.net/msf.688.334.

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In this work, we report on conducting polyaniline (PANI) nanostructures synthesized by a simplified template-free self-assembly method, which are doped with different oxidants such as ammonium persulfate (APS), FeCl3, Fe(NO3)3, and Fe2(SO4)3. It is found that the morphologies of the as-prepared PANI nanowires are dependent on the oxidant and the molar ratio of aniline to oxidant. The PANI nanostructures are semiconducting with room-temperature conductivity ranging from 10-2to 100S/cm, and the temperature dependence of conductivity follows three-dimensional Mott variable range hopping (3D Mott-VRH) model. In addition, the PANI pellets exhibit hydrophilic behavior.

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Калинин, Ю. Е., М. А. Каширин, В. А. Макагонов, С. Ю. Панков, and А. В. Ситников. "Влияние углерода на электрические свойства объемных композитов на основе окиси меди." Физика твердого тела 60, no. 4 (2018): 677. http://dx.doi.org/10.21883/ftt.2018.04.45674.272.

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AbstractThe effect of carbon filler on the electrical resistance and the thermopower of copper oxide-based composites produced by ceramic technology by hot pressing has been studied. It is found that the dependences of the electrical resistivity on the filler concentration are characteristic by S-like curves that are typical of percolation systems; in this case, the resistivity decreases more substantially as the carbon content increases as compared to the decrease in thermopower value, which is accompanied by the existence of the maximum of the factor of thermoelectric power near the percolation threshold. The studies of the temperature dependences of the resistivity and the thermopower at low temperatures show that, in the range 240–300 K, the predominant mechanism of the electrotransfer of all the composites under study is the hopping mechanism. At temperatures lower than 240 K, the composites with a nanocrystalline CuO matrix have a hopping conductivity with a variable hopping distance over localized states of the matrix near the Fermi level, which is related to the conductivity over intergrain CuO boundaries. A schematic model of the band structure of nanocrystalline CuO with carbon filler is proposed on the base of the analysis of the found experimental regularities of the electrotransfer.

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Giripunje, S. M., and Jyoti Ghushe. "Nanocomposite of Polyaniline and ZnO: Preparation, Characterisation, Optical and Electrical Properties." Journal of Nano Research 24 (September 2013): 123–32. http://dx.doi.org/10.4028/www.scientific.net/jnanor.24.123.

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ZnO nanoparticles were prepared by chemical method using starch as capping agent. Also the polyaniline-zinc oxide (PANI-ZnO) nanocomposites were prepared by in-situ polymerization of aniline monomer with ZnO nanomaterials. The structure and morphology of the ZnO nanoparticles were investigated by X-ray diffraction and scanning electron microscopy. X-ray diffraction revealed the wurtzite structure of ZnO. Average particle size of the ZnO nanoparticles were also calculated from XRD. SEM micrographs showed the spherical shape of ZnO nanoparticles. Band gap energy of ZnO nanoparticles was determined from UV absorbance spectra and confirm quantum confinement. In UV-Vis spectra of PANI salt, two absorption peaks are observed at 320 and 630 nm. These absorption peaks arises due to excitation of the benzene segment including amine structures in polyaniline. A considerable large red shift at 360 nm from 320 nm has been observed for PANI-ZnO nanocomposites. This prominent red shift might occur due to the interaction between the hydroxyl groups of ZnO and the quinoid ring of emeraldine salt. Transport properties of PANI-ZnO nanocomposites were studied in terms of transport parameters such as DC electrical conductivity (σ), charge localization length (α-1), most probable hopping distance ® and hopping energy (w) using variable range hopping model as described by Ziller to conducting polymers.

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33

Grillo, Alessandro, Enver Faella, Filippo Giubileo, Aniello Pelella, Francesca Urban, and Antonio Di Bartolomeo. "Temperature Dependence of Germanium Arsenide Field-Effect Transistors Electrical Properties." Materials Proceedings 4, no. 1 (November 15, 2020): 26. http://dx.doi.org/10.3390/iocn2020-07810.

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In this work, we report the fabrication of germanium arsenide () field-effect transistors with ultrathin channel and their electrical characterizations in a wide temperature range, from to . We show that at lower temperatures, the electrical conduction of the channel is dominated by the 3D variable range hopping but becomes band-type at higher temperatures, after the formation of a highly conducting two-dimensional (2D) channel. The presence of this 2D channel, limited to a few interfacial layers, is confirmed by the observation of an unexpected peak in the temperature dependence of the carrier density per area at . Such a feature is explained considering a model based on a temperature-dependent channel thickness, corroborated by numerical simulations, that show excellent agreement with the experimental data.

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Ding, Hang Jun, Zhou Yang, He Yang, Yun Ze Long, and Qing Guo He. "Polyaniline Nanostructures Doped with Fluorescent TPA-BTD-BN." Advanced Materials Research 807-809 (September 2013): 2679–83. http://dx.doi.org/10.4028/www.scientific.net/amr.807-809.2679.

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In this paper, a novel fluorescent material with high conductivity as 0.45 S·cm-1 and strong fluorescence has been successfully synthesized basing on polyaniline (PANI) nanostructures doped with a new prepared fluorescein TPABTDBN. The PANI nanostructures were prepared via a simplified template-free method (STFM) with FeCl3 as oxidant and dopant. The resulting sample was characterized by SEM, IR and fluorescence spectroscopy. The fluorescence intensity of synthesized composite improves with the increasing content of TPABTDBN. The electrical properties of pressed composite pellets were measured from room temperature about 291K down to 132K, the conductance follow the exponential temperature dependence of three-dimensional variable-range hopping (VRH) model.

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Fu, Ren Chun, Jun Du, Hui Huang, and Zhong Cheng Guo. "The Electrical Conductivity Stability of Polyaniline Doped with Three Different Acids." Advanced Materials Research 774-776 (September 2013): 803–6. http://dx.doi.org/10.4028/www.scientific.net/amr.774-776.803.

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The doping acid will obviously effect on the properties of polyaniline. In order to investigate the industrial acids influence the electrical conductivity stability of polyaniline, the hydrochloric acid (HCl), sulfuric acid (SA) and methanesulfonic acid (MSA) in industrial degree were chosen as doping acids to synthesize polyaniline. The stability of electrical conductivity was measured by in situ temperature. The mechanism of temperature dependence of electrical conductivity was discussed. The results revealed that the stability of polyaniline doped by hydrochloric acid (HCl) was better than that of polyaniline doped by other acids. The variable-range hopping (VRH) model could explain the temperature dependence of electrical conductivity of polyaniline.

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Barik, H. K., S. K. Ghorai, S. Bhattacharya, D. Kilian, and B. K. Chaudhuri. "Effect of Cr doping on the electrical conductivity and Seebeck coefficient in the superconductors obtained from the Bi–Pb–Sr–Ca–Cu–Cr–O-type glassy precursors by annealing." Journal of Materials Research 15, no. 5 (May 2000): 1076–82. http://dx.doi.org/10.1557/jmr.2000.0155.

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Homogenous (Bi3Pb)Sr3Ca3 (Cu4−nCrn)Ox (n 4 0 to 0.20) type glassy precursors become high-Tc superconductors by annealing at 840 °C. The suppression of Tc with increase of Cr concentration supports the pair-breaking mechanism. The feeble semiconducting behavior shown by the doped samples above their respective Tc values followed Mott's variable range hopping conduction mechanism. Like Ti- and Fe-doped samples, studied earlier, the thermoelectric power (TEP) of the present Cr-containing sample showed small positive peak above Tc, which was considered to be associated with the phonon-drag effect. The linear part of the temperature-dependent TEP (above Tc) well fitted the two-band model.

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Matsuura, Hideharu, Yuki Kondo, Kosuke Iida, Atsuki Hidaka, Shiyang Ji, Kazuma Eto, Kazutoshi Kojima, Tomohisa Kato, Sadafumi Yoshida, and Hajime Okumura. "Simple physical model for the sign of the Hall coefficient in variable-range hopping conduction in heavily Al-doped p-type 4H-SiC." Japanese Journal of Applied Physics 60, no. 3 (March 1, 2021): 031008. http://dx.doi.org/10.35848/1347-4065/abe645.

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KAR, MANORANJAN, and S. RAVI. "ELECTRICAL RESISTIVITY AND AC SUSCEPTIBILITY STUDIES IN Sr1-xLaxMnO3." Modern Physics Letters B 20, no. 24 (October 20, 2006): 1517–28. http://dx.doi.org/10.1142/s0217984906011542.

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Electron-doped Sr 1-x La x MnO 3(0≤x≤0.50) and hole-doped (x=0.70 and 0.82) samples have been prepared by solid state route. X-ray diffraction patterns could be refined using P63 space group for x≤0.30 and [Formula: see text] space group for x≥0.40. Temperature variation of AC susceptibility measurements show that all the electron-doped materials exhibit paramagnetic to ferromagnetic transitions with the transition temperatures ranging from 375 to 393 K, followed by low temperature antiferromagnetic transitions. The ferromagnetic maximum susceptibility is found to increase systematically with La doping, i.e. with increase in Mn 3+ ions. The high temperature resistivity data could be analyzed using the Mott-variable range hopping model. The hole-doped materials exhibit ferromagnetic to paramagnetic transition.

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Deepika and Hukum Singh. "Electrical conduction mechanism in films of Se80−xTe20Bix (0 ≤ x ≤ 12) glassy alloys." Canadian Journal of Physics 97, no. 2 (February 2019): 222–26. http://dx.doi.org/10.1139/cjp-2017-0973.

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This paper reports the study of DC electrical conductivity of films of Se80−xTe20Bix (0 ≤ x ≤ 12) glasses prepared using physical vapor deposition method. The films were structurally characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM results indicate the formation of nanorods within the films. The electrical conductivity of the samples was studied using Keithley electrometer in the temperature range 303–373 K. The results show that conduction in these samples takes place via thermally assisted tunnelling and variable range hopping of charge carriers corresponding to higher and lower temperature ranges, respectively. Further, it was found that the conductivity increases with increase in Bi concentration in Se–Te system. This has been explained on the basis of chemically ordered network model. It was also found that nanorod formation improves the electrical conductivity of Se–Te–Bi system compared to bulk Se–Te–Bi system.

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40

Sun, Bin, Hong Xing Yin, Meng Meng Li, Yun Ze Long, and Chang Zhi Gu. "Preparation, Electrical Conductivity, Photocurrent and Wettability of Carbon Microcoils." Advanced Materials Research 465 (February 2012): 125–31. http://dx.doi.org/10.4028/www.scientific.net/amr.465.125.

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In this paper, we report on fabrication and physical properties of carbon microcoils, which are prepared by a chemical vapor deposition (CVD) process with Ni-catalyzed pyrolysis of acetylene, and characterized by a scanning electron microscope, a transmission electron microscope and an infrared spectrometer. The dark electrical conductivity of an isolated carbon microcoil is about 81 S/cm at room temperature, and its temperature dependence follows three-dimensional Mott variable-range hopping (VRH) model. Particularly, evident photocurrent is observed in the carbon microcoil upon cameral flash illumination. In addition, it is found that the surface of microcoil film is hydrophobic, showing a large water contact angle of about 135°. These results indicate that carbon microcoils have excellent physical properties, and can be used as optoelectronic and reinforced materials.

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BASHIR, ABIDA, MOHD IKRAM, and RAVI KUMAR. "STUDIES OF TRANSPORT PROPERTIES OF RFe1-xNixO3 (x ≤ 0.5) WHERE R = Nd, Sm AND Gd." Modern Physics Letters B 25, no. 21 (August 20, 2011): 1787–94. http://dx.doi.org/10.1142/s0217984911027042.

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We present here the electrical transport properties of RFe 1-x Ni x O 3 (x ≤ 0.5) where R = Nd , Sm and Gd and the correlation between these systems. The resistivity increases as the rare ion is changed from Nd to Sm . The resistivity increases from the magnitude of the order of 103 to 106 Ωcm at lower temperatures and from 10 to 105 Ωcm as the temperature is increased. Also, the resistivity decreases as the concentration of Ni is increased within the ensemble showing a semiconducting behavior. The resistivity data is fitted with the Greaves Variable Range Hopping model which fits in the intermediate range of temperatures. There is decrease in gap parameter, increase in conductivity and increase in the density of states at Fermi level which clarify that the correlation length in the conducting network increases with the increase in Ni substitution. The Debye temperature decreases as the Ni concentration increases and follows the same trend as the rare earth ion is replaced.

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42

Salan, Ümit, Ahmet Altindal, Mustafa Bulut, and Özer Bekaroğlu. "Synthesis, characterization, electrical and dielectric permittivity measurements of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanines." Journal of Porphyrins and Phthalocyanines 10, no. 11 (November 2006): 1263–70. http://dx.doi.org/10.1142/s1088424606000636.

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2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanines were synthesized from 4-(4-amino-3-nitrophenoxy)phthalonitrile which was obtained from 4-nitro-1,2-dicyanobenzene and 4-amino-3-nitrophenol. 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) were synthesized in a one-step condensation reaction of ferrocenylaldehyde with 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), respectively. The novel compounds were characterized by elemental analysis, Inductively Coupled Plasma (ICP-MS), UV-vis, IR and 1 H NMR spectroscopy. The effects of temperature and frequency on the conduction properties (a.c. and d.c.) and the dielectric constant were studied on pellet samples of 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), with evaporated, ohmic gold electrodes in the frequency range 40-105 Hz. and within the temperature range 290-400 K. Unlike many metallophthalocyanines, a variable-range hopping model is found to most appropriately fit the experimental conductivity data of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), while for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), thermally activated conduction with single activation energy is valid. Frequency and temperature dependence of the a.c conductivity were analyzed in terms of existing theory for 2,9,16,23-tetra-(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II). It was found that the a.c. conductivity of the compounds depends on the frequency, obeying the empirical formula, σ ac = A ( T )ωs. The model parameters calculated are reasonable and consistent with the prediction of the correlated barrier hopping model for 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) and the quantum mechanical tunneling model for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II). The dielectric constant of the compounds increased with temperature and decreased with frequency in the investigated range.

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43

FIRDOUS, ARFAT, and M. M. AHMAD. "OPTICAL AND HIGH-TEMPERATURE ELECTRICAL PROPERTIES OF PURE AND Sr-MODIFIED CdS NANOCRYSTALS." International Journal of Nanoscience 11, no. 01 (February 2012): 1250009. http://dx.doi.org/10.1142/s0219581x12500093.

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Nanoparticles of CdS - and Sr -doped CdS were synthesized through chemical precipitation method using a high-boiling solvent. X-ray diffraction confirms the nanocrystallinity of the prepared nanostructures. The mean crystal size obtained by full width half maxima analysis is 3.34 nm for CdS , 3.39 nm for CdS:Sr (2 mM) and 3.41 nm for CdS:Sr (4 mM). The optical absorption analysis conducted in UV-vis range 200–900 nm reveals the transparency of these nanocrystals in the entire visible range but not in ultraviolet range. The results based on optical analysis yield bandgap values as 2.63 eV for CdS , 2.58 eV for CdS:Sr (2 mM) and 2.52 eV for CdS:Sr (4 mM) nanoparticles. This implies that pure CdS - and Sr -doped CdS are blue shifted with respect to the bulk CdS (2.42 eV), however Strontium modified CdS nanocrystals are red shifted with respect to pure CdS nanocrystals. The electrical conductivity data reveals semiconducting behavior of both pure CdS - and Sr -doped CdS nanocrystals. Fitting of conductivity data in Mott's variable range hopping model shows that Strontium doping in CdS reduces gap parameters from 2.81 to 2.59 eV.

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44

Tank, Tejas M., D. Bhargava, V. Sridharan, S. S. Samatham, V. Ganesan, and Sankar P. Sanyal. "Influence of Mn Site Substitution on Electrical Resistivity and Magnetoresistance Properties of Rare Earth Manganite." Advanced Materials Research 1047 (October 2014): 123–29. http://dx.doi.org/10.4028/www.scientific.net/amr.1047.123.

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We investigate the effects of Cr, Ru and Sn substitution on electrical resistivity and magnetoresistance property of polycrystalline samples La0.67Sr0.33Mn1-xBxO3(x = 0, 0.05; B= Ru, Cr and Sn) compounds. The value of M-I transition temperature (TP) decreases while resistivity increases with Cr, Ru and Sn substitution, moreover, the largest low-temperature magnetoresistance (MR %) is found at magnetic field dependent (Isotherm), which suggest that the spin-dependent scattering from internal grain regions is also responsible for the low-temperature MR %. Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of various transition metals in the Mn-site leads to a decrease in conductivity of the doped manganite samples, with conduction being controlled by the disorder induced localization of charge carriers.

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45

Reddy, Y. S. "Electrical transport and magnetoresistance of double layered CMR manganites R1.2Sr1.8Mn2O7(R = La, Pr, Sm)." Materials Science-Poland 35, no. 2 (July 26, 2017): 440–46. http://dx.doi.org/10.1515/msp-2017-0048.

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Abstract Polycrystalline bulk samples of double layered (DL) colossal magnetoresistive (CMR) manganites R1.2Sr1.8Mn2O7 (R = La, Pr, Sm) were prepared by sol-gel method to study the effect of size of lanthanide ion on their magnetotransport properties. The electrical resistivity of the samples was investigated in the temperature range of 70 K to 300 K at different magnetic fields. The samples LSMO and PSMO show insulator-to-metal transition (IMT) behavior, while SSMO sample exhibits insulating behavior in the entire temperature range with a very large value of resistivity. The insulator-to-metal transition temperature (TIM) decreases from 123 K (LSMO) to 90 K (PSMO) and disappears in SSMO sample. To explain the electrical transport above TIM, the temperature dependent resistivity data (T > TIM) of all the samples were fitted to the equations of different conduction models. The results indicate that the conduction at T > TIM is due to Mott variable range hopping (VRH) mechanism in the LSMO and PSMO samples, while Efros-Shkloskii (ES) type of VRH model dominates the conduction process in the SSMO sample. All the three samples show increasing magnetoresistance (MR) even below TIM and the maximum MR is shown by LSMO (39 % at 75 K, 3 T).

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46

Feres, Flavio H., Lucas Fugikawa Santos, and Giovani Gozzi. "Temperature and Electric Field Influence on the Electrical Properties of Light-Emitting Devices Comprising PEDOT:PSS/GPTMS/Zn2SIO4:Mn Composites." MRS Advances 3, no. 33 (2018): 1883–89. http://dx.doi.org/10.1557/adv.2018.179.

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ABSTRACTIn the present study, we analyze the influence of temperature and active layer thickness on the electrical properties of electroluminescent devices comprising a polymeric conductive blend (poly(3,4 ethylenedioxythiophene):polystyrene sulfonate, PEDOT:PSS), an inorganic electroluminescent material (manganese doped zinc orthosilicate, Zn2SiO4:Mn) and an organosilicon material (3-glicidoxypropyltrimethoxysilane, GPTMS), manufactured at different weight ratios of the component materials. The devices were obtained by depositing the active layer by drop-casting onto ITO-coated (RF-sputtering) glass substrates and thermally evaporating gold top electrodes in high vacuum. The results show that 90 wt% Zn2SiO4:Mn is required to observe high electroluminescence from the fabricated devices and that the optimum performance (turn-on voltage of 33 V, luminous efficacy of 24 cd/A and maximum luminance of almost 2000 cd/m2) was achieve for a (9.5/0.5/90) (GPTMS/PEDOT:PSS/Zn2SiO4:Mn) weight ratio. The device turn-on voltage found to be as proportional to the thickness of the active layer, indicating that the electroluminescence occurs by a field-effect mechanism. The temperature variation in the 100-300 K range allowed us to develop a theoretical model for the device operation, where the charge carrier transport in the active layer is well described by the variable range hopping model, with luminous efficacy nearby independent of the temperature.

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Zhang, Li, Yibao Li, Zhen Tang, Yan Deng, Hui Yuan, Jiangying Yu, and Xuebin Zhu. "Magnetic and electrical transport properties of Sr2Ti1−xCoxO4 ceramics by sol–gel." Modern Physics Letters B 31, no. 17 (June 8, 2017): 1750195. http://dx.doi.org/10.1142/s0217984917501950.

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Microstructures, electrical transport and magnetic properties of Sr[Formula: see text]Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] ceramics are investigated. With Co doping, the Sr[Formula: see text]Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] ceramics remain tetragonal structure while the grain size is decreased with doping. Magnetic moment is enhanced with Co doping and ferromagnetism is observed at low temperatures for Co-doped Sr[Formula: see text]TiO[Formula: see text]. The Sr[Formula: see text]Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] and Sr[Formula: see text]Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] show semiconductor-like transport properties, which can be well fitted by Mott variable range hopping model. The results will provide an effective route to synthesize Sr[Formula: see text]Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] ceramics as well as to investigate the physical properties.

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Kawahara, T., S. Tamura, H. Inai, Y. Okamoto, and J. Morimoto. "Thermoelectric Properties and Power Factor of YBa2Cu3O6+xwith Rare-earth Dopants." Journal of Materials Research 14, no. 4 (April 1999): 1200–1203. http://dx.doi.org/10.1557/jmr.1999.0163.

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Both the thermoelectric power and the resistivity of the oxygen deficient YBa2Cu3O6+x samples were measured. The rare-earth-doped samples, such as Sm and Dy, whose magnetic moments in the +3 valence state are different, were studied. Then the power factor of the thermoelectric ability was calculated. The power factor of the Dy-doped samples is smaller than those of the other samples, especially at high temperature. This smallness of the power factor is the main reason why the Dy-doped samples have larger resistivity. We try to analyze the data by the theoretical expression under the variable range hopping conduction model. The expression of the thermoelectric power could be fit for the nondoped and Sm-doped samples, except at low temperature. In this situation, the thermoelectric power increases as temperature increases, and this temperature dependence is good for the thermoelectric materials at high temperature where the resistivity decreases with temperature increasing.

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Ala-Nissila, T., Debashish Chowdhury, and J. D. Gunton. "Models of hopping-controlled reactions with variable hopping range." Physical Review A 34, no. 5 (November 1, 1986): 4251–55. http://dx.doi.org/10.1103/physreva.34.4251.

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50

Zhai, Yong-Qing, Jing Qiao, and Zhang Zhang. "Magnetic and Electrical Transport Properties of Double Perovskite Sr2FeMoO6Prepared by Sol-Gel Method." E-Journal of Chemistry 8, s1 (2011): S189—S194. http://dx.doi.org/10.1155/2011/984862.

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With activated carbon for reducing agent, the sol-gel method was used to prepare the giant magnetoresistance materials Sr2FeMoO6, which is the double Perovskite oxide. The structure, morphology, magnetic and electrical transport properties were investigated respectively by x-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The as-synthesized sample is Sr2FeMoO6with tetragonal crystal structure and I4/mmm space group and unit cell parameter is a = 5.580Å, c = 7.882Å. The primary particles are spherical in shape and the grain size is below 100 nm. The curie temperature is above room temperature and the saturation magnetization is 13.321 A·m2/kg under 1.0 T at room temperature. The sample exhibit typical semiconductor behavior and the conductive mechanism can be described by small polaron variable range hopping model. The room temperature magnetoresistance of the sample under 1.0 T field is up to -10.02%. Moreover, it is found the dosage of citric acid and the amount of reducing agent has great effect on the phase structure and magnetic properties of the samples.

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Journal articles on the topic 'Variable-range hopping model'

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