Temperature Dependence Of Electrical Conductivity Research Articles

Nonlinear Thermopower Behaviour of N-Type Carbon Nanofibres and Their Melt Mixed Polypropylene Composites.

The temperature dependent electrical conductivity σ (T) and thermopower (Seebeck coefficient) S (T) from 303.15 K (30 °C) to 373.15 K (100 °C) of an as-received commercial n-type vapour grown carbon nanofibre (CNF) powder and its melt-mixed polypropylene (PP) composite with 5 wt.% of CNFs have been analysed. At 30 °C, the σ and S of the CNF powder are ~136 S m−1 and −5.1 μV K−1, respectively, whereas its PP/CNF composite showed lower conductivities and less negative S-values of ~15 S m−1 and −3.4 μV K−1, respectively. The σ (T) of both samples presents a dσ/dT < 0 character described by the 3D variable range hopping (VRH) model. In contrast, their S (T) shows a dS/dT > 0 character, also observed in some doped multiwall carbon nanotube (MWCNT) mats with nonlinear thermopower behaviour, and explained here from the contribution of impurities in the CNF structure such as oxygen and sulphur, which cause sharply varying and localized states at approximately 0.09 eV above their Fermi energy level (EF).

Temperature dependences of electrical conductivity and magnetic susceptibility of crystals of solid solution Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=--Bi-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=-

Solid solutions Bi2Te3-Sb2Te3 continue to be the subject of numerous and versatile experimental studies due to their practical importance for thermoelectric materials science. In this regard, the problem of studying the regularities of changes in the state of the electronic system of these semiconductors from composition and temperature remains urgent. This paper presents the results of studying the temperature dependences of the magnetic susceptibility of Bi2Te3-Sb2Te3 crystals containing 10, 25, 40, 50, 60 mol.% Sb2Te3. The correlation of the behavior of the temperature dependences of the magnetic susceptibility and electrical conductivity is analyzed. Keywords: magnetic susceptibility, diamagnetic susceptibility, temperature dependence of electrical conductivity.

Influence of external factors on the electrical conductivity of Bi2Te2.5Se0.5

The mechanism of intrinsic and impurity electrical conductivity of semiconductors based on Bi2Te2.5Se0.5 has been elucidated. The nature and reasons for the dependence of electrical conductivity on various external influences are considered. In this case, the temperature dependence of electrical conductivity, light absorption and photoconductivity of Bi2Te2.5Se0.5 were used as external influences. And also the influence of the electric field was studied and it was found that in this case the value of the critical energy is 107V/m.

Thermoelectric properties of (CuInSe-=SUB=-2-=/SUB=-)-=SUB=-1-x-=/SUB=-(In-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=-)-=SUB=-x-=/SUB=- solid solutions

The results of studying the temperature dependences of electrical conductivity, thermoelectric coefficient, Hall mobility of charge carriers, total and electronic thermal conductivity, as well as the phonon thermal resistance of alloys of solid solutions (CuInSe2)1-x(In2Te3)x, where x=0.005 and 0.0075. The values of these parameters for certain temperatures were used to calculate the values of the thermoelectric figure of merit of the indicated compositions. It turned out that with an increase in temperature, the thermoelectric figure of merit tends to grow strongly, which is why it can be concluded that these materials can be used in the manufacture of thermoelements. Keywords: solid solutions, scattering mechanisms, three-phonon processes, thermoelectric efficiency.

The influence of carbon black content on temperature dependences of electrical conductivity of polymer composite

It was found that in the region of the percolation threshold, depending on the dominance of one or another conduction mechanism, the temperature dependence of the specific volume resistivity rho(T) of the polymer composite based on a matrix of ethylene vinyl acetate is significantly transformed. With an increase in the CB content, there is a decrease by several orders of magnitude in the maximum value of the relative resistivity rho(T)max/rho20 in its temperature dependence. Peroxide crosslinking of matrix macromolecules leads to a change in the nature of the temperature dependence of resistivity. Keywords: polymer composites, carbon black, electrical conductivity, temperature dependence.

Термоэлектрические свойства твердых растворов (CuInSe-=SUB=-2-=/SUB=-)-=SUB=-1-x-=/SUB=-(In-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=-)-=SUB=-x-=/SUB=-

The results of studying the temperature dependences of electrical conductivity, thermoelectric coefficient, Hall mobility of charge carriers, total and electronic thermal conductivity, as well as phonon thermal resistance of alloys of (CuInSe2)1-x(In2Te3)x solid solutions at x=0.005 and 0.0075 are presented. The values ​​of these parameters for certain temperatures were used to calculate the values ​​of the thermoelectric figure of merit of the indicated compositions. It turned out that as the temperature rises, the thermoelectric figure of merit tends to grow strongly, from which it can be concluded that these materials can be used in the manufacture of thermoelements.

Features of changes in electrophysical properties of cadmium antimonide when irradiated with 60Co Gamma-quanta

The effect of radiation defects in specially non-doped and tellurium-, indium-doped crystals of cadmium antimonide before and after high doses of 60Co γ-quanta irradiation was studied on the basis of measurements and analysis of temperature dependences of electrical conductivity, Hall effect in the temperature range (78–295)K. Gamma-irradiation with high doses leads to significant changes in electrophysical properties. The mechanisms responsible for these changes are established and a theoretical explanation of these effects is given.

Mechanical damage and thermal effect induced by ultrasonic treatment in olive leaf tissue. Impact on polyphenols recovery

The influence of ultrasound treatment (US) on cellular damage of olive leaf tissue was studied. Mechanical damage and thermal effect of US were characterized. The level of tissue damage was defined by the diffusivity disintegration index ZD based on the diffusivity of solutes extracted from olive leaves differently treated. The Arrhenius form using the temperature dependences of the thermal treatment time within the temperature interval 20–90 °C was observed for the thermal process. The corresponding activation energy ΔUT was estimated as 57 kJ/mol. The temperature dependences of electrical conductivity were measured for extracts of intact and maximally treated olive leaves. Then the diffusivity disintegration index ZD and total phenolic compounds recovery for three studied US powers were calculated (100, 200, and 400 W). The results evidenced that the mechanically stimulated damage in olive leaf tissue can occur even at a low US power of 100 W if treatment time is long enough (t = 3.5 h). The US treatment noticeably accelerated the diffusion process mechanically in addition to its thermal effect. Trials in aqueous solution revealed the dependence of polyphenols extraction on damage level with respect to the US power applied.

Entropy Reduced Charge Transport and Energy Loss in Interfacial Zones of Polymer Nanocomposites

Polymer nanocomposites have higher energy storage density, much lower conductivity, and energy loss than the polymer matrices. The excellent performance may be originated from the deep-level localized states introduced by the interfacial zones between nanofillers and polymer matrices. However, the essential relation between the deep-level localized states and the composition, architecture, and configuration of polymer chains is still not clear. We investigate the temperature dependences of electrical conductivities of three types of energy storage polymer nanocomposites and find that they all obey the Meyer-Neldel (MN) compensation rule and the prefactor has an exponential relationship with the MN energy. It is found that the kinetic energy of electrons in the extended states of nanocomposites is the MN energy, which is related to the excitation of electrons by optical phonons. We propose to redefine the energy of localized states by the energy of optical phonons and the entropy of molecular conformations. It is found that the shape parameter of localized state distribution is related to the optical phonons and controlled by the composition, structure, and configuration of polymer chains, while the density of localized states is determined by the conformation and aggregate structure. We propose an optical phonon and entropy activated charge transport model, and the obtained conductivity equation is consistent with the experimental results. The entropy of molecular conformations can be used as a key factor to tailor the conductivity and energy loss of polymer nanocomposites. It provides a new perspective to study how to improve the energy storage performance of polymer nanocomposites.

Correlation between structural, electrical and electrochemical performance of Zn doped high voltage spinel LiNi0.5-xZnxMn1.5O4 porous microspheres as a cathode material for Li-Ion batteries

This work reports on the structural, electrical and electrochemical properties of Zn doped LiNi0.5-xZnxMn1.5O4 (x = 0.0, 0.05, 0.1 and 0.2) porous microspheres cathode materials obtained by a hydrothermal route followed by low-temperature annealing. Structural properties are investigated by X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectroscopy; scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman, and Fourier transform infrared (FTIR) spectroscopy. The XRD patterns and NMR studies further demonstrate the successful incorporation of Zn into the spinel structure. SEM reveals morphology with porous spheres with a size range of 0.2 μm – 1 μm. Temperature dependent electrical conductivity was measured by impedance spectroscopy. The activation energies of total conductivity are determined as 0.41, 0.41, 0.47, and 0.48 eV for x = 0, 0.05, 0.1, and 0.2, respectively. Influence of Zn doping on the grain, grain boundary and total conductivities of LiNi0.5-xZnxMn1.5O4 were analyzed through brick-layer model. The grain conductivity increases with Zn content, whereas the total conductivity increases till x = 0.1. Overall, electrical properties of LiNi0.5-xZnxMn1.5O4 are governed by grain boundary conduction. Increasing the Zn content up to x = 0.1 in LiNi0.5-xZnxMn1.5O4 leads to an increment in specific capacity at a 1C rate. Among them, the LiNi0.4Zn0.1Mn1.5O4 exhibits a high discharge capacity of 114 mAh g−1 at 1C with capacity retention of 91.5% after 50 cycles. We also investigated the effect of Zn doping on Li+ ion diffusivity and observed improved Li+ ion diffusion (7.4⋅10−13 cm2 s−1) for LiNi0.4Zn0.1Mn1.5O4. Based on these electrochemical studies it is proposed that this material can be utilized as a cathode in Li-ion batteries for high-power applications.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Tunable thermo-sensitive electrical conductivity of melt-mixed PA- 12/PP-MWCNT nanocomposites

In this study, the correlation of morphology, temperature dependent electrical conductivity and solid-state relaxation dynamics of melt-mixed polyamide 12 (PA-12)/polypropylene-multi walled carbon nanotube (PP-MWCNT) based ternary nanocomposites has been systematically investigated. Selectively confined functionally conductive masterbatch dispersed in nylon matrix with structurally ordered co-continuous morphology enhanced the electrical conductivity due to double percolation phenomenon by virtue of their differences in melt viscosity, polarity, surface energy and similar processing window of PA-12 and PP-MWCNT. The stability of the conducting polymer nanocomposites and the correlation of temperature sensitive electrical behaviour with the endothermic transitions and dynamic-mechanical relaxation transitions in the temperature range of −20 °C–200 °C is also explored. Polymer nanocomposite based thermo-sensitive materials substantiated four distinct regimes highlighting the network build-up or restoration assisted conductivity. Our study demonstrates the tunability of temperature dependence of electrical conductivity by controlling conducting channels via manipulating the ratio of PA-12 to PP-MWCNT composite filler for temperature dependent current terminating electrical devices. The reproducibility of such temperature sensitivity has also been explored.

Surface morphology-modulated electrical conductivity behavior in 2D anisotropic exfoliated nanoribbons

Although mechanical exfoliation allows the preparation of flakes of two-dimensional (2D) layered materials from their bulk counterparts in a cost-efficient and versatile manner, it has been difficult to correlate the surface morphology of the exfoliated flakes with their fundamental electrical characteristics. In this study, we used mechanical exfoliation to prepare 2D layered titanium trisulfide (TiS3) nanoribbons having thicknesses varying from a few to tens of nanometers. Interestingly, the bulk electrical conductivity of the exfoliated TiS3 nanoribbons was correlated to their surface roughness, rather than their thickness. Furthermore, at temperatures from 80 K to 280 K, the distinctive behavior of the electrical conductivity in the exfoliated nanoribbons was also significantly dependent on the surface roughness. Measurements of intrinsic field-effect electron mobilities unveiled that the dominant mobility scattering mechanism transitioned from phonon scattering to coulombic and/or surface roughness scattering upon increasing the surface roughness, thereby resulting in distinctive temperature-dependent electrical conductivity behavior. Accordingly, simple measurements of surface morphologies can provide information regarding the fundamental electrical properties of 2D exfoliated layered flakes, potentially leading to greater use of layered materials in semiconductor applications.

Water enrichment/depletion of amorphous carbon coatings probed by temperature-dependent dc electrical conductivity and Raman scattering

Amorphous carbon (a-C) is an appealing disordered multi-phase material widely used as a cost-effective barrier coating (10–100 nm thick) for silica optical fibers to protect them from harsh environments. Those coatings prevent strength degradation of the optical fibers by moisture and, also block hydrogen diffusion into the fiber. In this paper, we experimentally study the in situ temperature-dependent dc electrical conductivity and Raman scattering of dried/wetted a-C coatings under multiple heating/cooling cycles within the range of 40–120 °C. At temperatures of above 80 °C, we observe hysteresis in both the dc electrical resistance and the Raman scattering intensity. One of the mechanisms is related to the escape of intercalated (or spatially confined) water from the a-C coating, causing the resistance decrease due to a closing of the bandgap. The opposite is observed when some water molecules experience dissociative absorption at the edge and basal defects that may be decorated with CH, COOH/COH and COC/CO functional groups. The content of water within the a-C coating is quantified through relative contributions of the water and edge defect related Raman bands. This study expands our knowledge about a-C ultrathin films, originally designed as barrier coatings, towards promising ultracompact humidity sensors and next-generation adsorbents.

Investigation of doping effect on electrical conduction mechanism and Li+ ion insertion/extraction in ZnO-XV2O5 {X=5% and 10%} electrode for superior energy storage application

In an effort to enhance the electrical conductivity and electrochemical charge storage capacity of pure ZnO, the multivalent V2O5 is doped with different percentage by solid-state synthesis procedure with low annealing temperature. The materials are characterized by the X-ray diffraction (XRD) and the Fourier Transform Infrared Spectroscopy (FTIR). The XRD pattern reveals hexagonal wurtzite structure with preferred orientation along (101) plane. Three secondary phases Zn3(VO4)2, Zn4V2O9 and ZnV3O8 appear after V2O5 doping. The vibrational bending and stretching modes are identified by the Fourier Transform Infrared Spectroscopy (FTIR). The temperature dependent electrical conduction mechanism of ZnO–V2O5 (ZNV) varistor ceramic materials is studied by ac impedance spectra analysis. The effect of doping on the electrical conductivity formalism was well discussed. By Nearest Neighbor hopping (NNH) model, it is shown that activation energy of ZnO gradually decreased from 0.28 eV to 0.21 eV by introducing V2O5. The electrochemical properties of as prepared ZNV electrodes are investigated by Cyclic voltammetry (CV), Galavanostatic charge-discharge (GCD) and Electrochemical Impedance Spectra (EIS) analysis. In 1 M Li2SO4 electrolyte the ZnO–10%V2O5 (ZNV10) shows maximum specific capacitance 447 F/g at current density 1 A/g. The cyclic stability of pure ZnO, ZnO-5% V2O5 (ZNV5) and ZnO–10%V2O5 (ZNV10) are tested for 1000 cycles. The capacity retention ratio of pure ZnO increases from 68% to 88% after 10% V2O5 doping. The charge storage mechanism of ZNV10 is demonstrated by Faradaic adsorption/desorption through the redox charge transfer process. This work may provide a new scope for further development of pseudocapacitor electrode for high performance supercapacitor.

Design, structural evolution, optical, electrical and dielectric properties of perovskite ceramics Ba1-xBixTi1-xFexO3 (0 ≤ x ≤ 0.8)

The ceramics with perovskite structure of the compositions Ba1-xBixTi1-xFexO3 (x = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized through the conventional solid-state reaction route. All prepared samples were characterized by X-ray diffraction, Raman spectroscopy, UV–visible spectroscopy and impedance spectroscopy. The X-ray diffraction characterization at room temperature indicated the formation of perovskite phase in all the samples. The X-ray diffraction data refined by Rietveld technique revealed two phase transitions with the increase of BiFeO3 content, the first structural transformation from tetragonal (P4mm) to cubic (Pm3‾m) and the second from cubic (Pm3‾m) to rhombohedral (R3c), which were confirmed by Raman spectroscopy. UV–vis absorption spectra of doped compounds indicated the presence of four electronic transitions in octahedrally coordinated Fe3+ ions from their fundamental 6A1g(S) level to different excited levels. The co-doping of Bi3+ and Fe3+ ions from 0% to 80 mol% leads to a decrease of the direct band gap energy from 3.29 to 1.91 eV, and a shift of the band gap edges, namely the conduction band minimum and valence band maximum. The impedance results suggest that both grain (G) and grain boundary (GB) contribute to the total conductivity and the effect of this latter increases with (Bi, Fe) content. Additionally, the Nyquist plots showed the negative temperature coefficient of resistance (NTCR) and the temperature-dependent dc electrical conductivity demonstrated the semiconducting nature for all samples. The sample x = 0.4 exhibited the highest dc electrical conductivity. The activation energy values revealed that the conduction mechanism is dominated by ionized oxygen vacancies. The changes of dielectric properties at room temperature with increasing BiFeO3-doping amount are discussed.

Cation Diffusion in Non-Stoichiometric (La, Sr)MnO3/CeO2 Nano-Composite Cathode

Co-sintering of stacks or cells containing electrodes, electrolytes, and separators is essential fabrication technology to improve power density per unit volume significantly. Generally, cathode materials have low heat-resistant temperatures, and they are easily decomposed or degraded by sintering at a high temperature. (La0.8Sr0.2) MnO3 (LSM) shows relatively high resistance and preferable low-reactivity with fluorite electrolytes during sintering at a high temperature. But it shows lower cathodic properties than lanthanum strontium cobaltite or lanthanum strontium cobalt ferrite because of poor oxygen diffusion. Thus, we have investigated LSM/ceria nanocomposite to improve oxygen diffusion.Nanocomposite precursor powder containing LSM and ceria was synthesized by glycine method. The composite ratio of LSM and ceria was fixed at 9:1 (molar ratio). The dense composite compact was obtained by sintering the powder at 1200oC for 5 h in air, and fine ceria particles were homogeneously dispersed with LSM. Electrical conductivity and oxygen diffusion coefficient were estimated with these dense composites. Oxygen diffusion coefficients were estimated by electrical conductivity relaxation method. The amount of cation dissolved in ceria was investigated from XRD peak shifts. The defect of La or Sr in LSM formed by sintering with ceria was estimated with magnetic properties of LSM and LSM/ceria nanocomposite. The defect was also investigated using the relationship between activation energy and composition of a-site defect LSM or La-defect LSM.LSM showed a low oxygen diffusion coefficient, and the coefficient of LSM/ceria nanocomposite was much improved even though ceria composite ratio is 10%. However, LSM/ceria composite showed much lower conductivity than LSM since a-site cation of LSM, La or Sr, may be easily diffused into ceria. XRD peaks derived from only ceria were shifted toward lower angle for LSM/ceria nanocomposite prepared under various sintering conditions. The shift revealed that 2-5% La in LSM was diffused into ceria, assuming that only La is diffused. Diffusion of La into ceria increases in oxide ionic conductivity and the diffusion would benefit the composite's cathodic properties in terms of oxygen diffusion. However, if the diffusion would bring about La defect LSM and deviations from the optimum composition, the diffusion would be detrimental in terms of electrical conductivity.Then we investigated the effects of the diffusion on the defect structure of LSM in LSM/ceria nanocomposite by magnetic properties and electrical conductivities. Assuming that only La of LSM was diffused into ceria, the loss amount of La from LSM was estimated with magnetic phase transition temperatures for LSM and LSM/ceria nanocomposite. The temperatures were measured by SQUID. The overall loss amount of La from LSM was increased according to solid solution of La in ceria. But, the loss amount was slightly different from the solution amount to ceria.The ionic radius of Sr2+ is similar to that of La3+. Dissolution of Sr in ceria also leads to XRD peaks shift toward lower angle as well as that of La. Then, we investigate whether the loss from LSM was derived from only La (La-defect LSM) or both La and Sr ( a-site-defect LSM). La-defect and a-site-defect LSM dense ceramics with various defect concentrations were prepared by glycine method. Activation energy of these LSM ceramics was estimated from the temperature dependence of electrical conductivity measured in air. That of La-defect LSM was monotonically decreased with increasing defect concentration. A-site-defect LSM showed no significant change in activation energy within the defect concentration less than 8%. The relationship between activation energy of LSM/ceria nanocomposite and the defect concentration of LSM was measured using various sintering conditions. The relationship showed the activation energy of LSM/ceria was almost independent of the defect concentration. Therefore, Sr would simultaneously diffuse from LSM to ceria during sintering LSM/ceria nanocomposite. Electrical degradation of LSM/ceria nanocomposite would be derived from Sr defect of LSM as well as La.

Structural and dc electrical transport study of Cu-Zn ferrialuminates prepared by chemical route

Ferrimagnetic ionic crystalline materials, with general formula AB2O4are termed as spinel phase ferrites. Electro – magnetic properties, concentration of different ions and surface morphology of mixed–metal oxides shows significant applications in the various fields. In above work, Cu doped Zn ferrialuminate were prepared by sol-gel auto-combustion route. Purity of the synthesized materials were confirmed by XRD analysis which reveals the formation spinal phase structure and by applying the Debye-Scherer’s formula. Nanocrystalline nature of the samples were studied by transmission electron microscopy (TEM). The particle was found in the nanorange. The temperature dependent DC electrical conductivity was studied by two probe method. Semiconductor behavior with the rise in temperature were found in all the samples.

Signature of strong localization and crossover conduction processes in doped ZnO thin films: synergetic effect of doping fraction and dense electronic excitations

Ga x Zn1−x O thin films with varying Ga fraction within the solubility limit were irradiated with high-energy heavy ions to induce electronic excitations. The films show good transmittance in the visible region and a reduction of about 20% in transmittance was observed for irradiated films at higher ion fluences. The Urbach energy was estimated and showed an augmenting response upon increase in doping fraction and ion irradiation, this divulges an enhancement of localized states in the bandgap or disorder in the films. The evolution of such localized states plays a vital role in charge transport and thus the temperature dependent electrical conductivity of irradiated thin films was studied to elucidate the dominant conduction mechanisms. The detailed analysis unfolds that in the high-temperature regime (180 K < T < 300 K), the charge conduction was dominated by thermally activated band conduction followed by the nearest neighbor hopping (NNH) mechanism. Whereas in the lower temperature regime (25 K < T < 170 K), the conduction mechanism was governed by Mott-VRH (variable range hopping) followed by Efros–Shklovskii (ES)-VRH. A sudden and steep rise in resistivity below 30 K was observed for GZO films with higher doping fraction at higher ion fluence and proclaims the presence of strong localization of carriers.

Effect of cobalt content on the properties of quintuple perovskites Sm2Ba3Fe5-xCoxO15-δ

Quintuple perovskites Sm2Ba3Fe5-xCoxO15-δ (x ​= ​0.5, 1.0 and 1.5) have been prepared by glycerin-nitrate technique in air. The phase purity was confirmed by XRD. Partial substitution of Co for Fe decreases the oxygen content and thus the mean oxidation state of 3d-metals. It also slightly decreases the thermal expansion coefficient of oxides. Positive value of the Seebeck coefficient confirmed p-type conductivity, though the thermopower decreases as the Co content increases. The temperature dependence of electrical conductivity reveals a maximum at 550–750°С.