scholarly journals DC conductivity and Seebeck coefficient of nonstoichiometric MgCuZn ferrites

2017 ◽  
Vol 35 (1) ◽  
pp. 40-44 ◽  
Author(s):  
W. Madhuri ◽  
S. Roopas Kiran ◽  
M. Penchal Reddy ◽  
N. Ramamanohar Reddy ◽  
K.V. Siva Kumar
Keyword(s):  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Small Polaron ◽  
X Ray Diffraction ◽  
High Definition ◽  
Conventional Solid State Reaction ◽  
Polaron Hopping ◽  
Dc Electrical Conductivity ◽  
Phase Spinel ◽  
Diffraction Patterns

AbstractNonstoichiometric series of Mg0.5−xCuxZn0.5Fe1.9O4−δ where x = 0.0, 0.1, 0.15, 0.2 and 0.25 has been synthesized by conventional solid state reaction route. The single phase spinel structure of the double sintered ferrites was confirmed by X-ray diffraction patterns (XRD). The ferrite series was studied in terms of DC electrical conductivity and thermoelectric power in the temperature ranging from room temperature to 300 °C and 400 °C, respectively. It was observed that DC electrical conductivity and Seebeck coefficient α decreased with the increase in x. DC electrical conductivity was found to decrease by about 4 orders. All the compositions showed a negative Seebeck coefficient exhibiting n-type semiconducting nature. From the above experimental results, activation energy and mobility of all the samples were estimated. Small polaron hopping conduction mechanism was suggested for the series of ferrites. Owing to their low conductivity the nonstoichiometric MgCuZn ferrites are the best materials for transformer core and high definition television deflection yokes.

Characterization of Cathode Materials Ln0.7Sr0.2Ca0.1Co0.7Fe0.3O2.85 (Ln=La, Pr and Nd) Synthesized by Microwave Sintering Techniques

2013 ◽  
Vol 771 ◽  
pp. 59-62
Author(s):  
Jie Zhao ◽  
Jiang Fu ◽  
Yong Fu ◽  
Yu Na Zhao ◽  
Yong Chang Ma
Keyword(s):  
Electrical Conductivity ◽  
Cathode Materials ◽  
Small Polaron ◽  
Microwave Sintering ◽  
X Ray Diffraction ◽  
Mixed Conductivity ◽  
Polaron Hopping ◽  
Expansion Behavior ◽  
Higher Temperature

Sr, Ca and Fe doped cathode materials Ln0.7Sr0.2Ca0.1Co0.7Fe0.3O2.85 (LnSCCF, Ln=La, Pr and Nd; abbreviated as L-72173, P-72173 and N-72173) were synthesized by microwave sintering (MWS) techniques. The formation process, phase structure and composition were characterized using TG/DTA, XRD and EDS. The thermal expansion behavior of the samples was analyzed in the range of 20-950 °C by thermal dilatometer. The electrical conductivity of the samples was measured with DC four-terminal method from 25 to 900 °C. The X-ray diffraction shows that the samples exhibit a single phase with rhombohedral or cubic perovskite structure after sintered at 1200 °C for 20 min. The electrical conductivity of the samples increases with temperature up to a maximum, and then decreases gradually at higher temperature owing to the creation of oxygen vacancies. The small polaron hopping is regarded as the conducting mechanism (T 550 °C). L-72173 has higher mixed conductivity ( >300 S·cm-1) in 550-800 °C. The average TECs of L-72173, P-72173 and N-72173 are 1.389× 10-5 K-1, 1.417 × 10-5 K-1 and 1.416 × 10-5 K-1 in the range of 25-800 °C, respectively. They are thermally matched to the GDC better than the YSZ and SDC.

scholarly journals Thermoelectric Properties of Ca3Co2−xMnxO6 (x = 0.05, 0.2, 0.5, 0.75, and 1)

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 497 ◽  
Author(s):  
Nikola Kanas ◽  
Sathya Singh ◽  
Magnus Rotan ◽  
Temesgen Desissa ◽  
Tor Grande ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Properties ◽  
Self Assembly ◽  
Intermediate Phase ◽  
Small Polaron ◽  
Solid State Method ◽  
Polaron Hopping ◽  
Seebeck Coefficients ◽  
Conventional Sintering

High-temperature instability of the Ca3Co4−yO9+δ and CaMnO3−δ direct p-n junction causing the formation of Ca3Co2−xMnxO6 has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca3Co2−xMnxO6 with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca3CoMnO6 (x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S·cm−1 at 900 °C for x = 0.05. The material Ca3Co1.8Mn0.2O6 (x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca3Co2−xMnxO6 layers between Ca3Co4−yO9+δ and CaMnO3−δ open for new geometries and designs of oxide-based thermoelectric generators.

Strontium Dopant Concentrations Influence on Nd1-xSrxMnO3±δ Structural and Electrical Conductivity

2010 ◽  
Vol 660-661 ◽  
pp. 636-640
Author(s):  
Reinaldo Azevedo Vargas ◽  
Rubens Chiba ◽  
Marco Andreoli ◽  
Emília Satoshi Miyamaru Seo
Keyword(s):  
Electrical Conductivity ◽  
Perovskite Structure ◽  
Small Polaron ◽  
Ceramic Materials ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
X Ray Diffraction ◽  
Polaron Hopping ◽  
Different Types ◽  
Fuel Cell Cathode

Many different types of ceramic materials are currently being studied as possible cathodes in Solid Oxide Fuel Cells (SOFC), in an attempt to reduce operating temperatures. Strontium-doped neodymium manganite (Nd1-xSrxMnO3±δ) was used as an intermediate temperature solid oxide fuel cell cathode. X-ray diffraction and electrical conductivity of the Nd1-xSrxMnO3±δ system with a perovskite structure were studied in function of x equal to 0.10, 0.30 and 0.50. An orthorhombic pseudo-perovskite structure was assigned to all powder compositions prepared by standard ceramic technique. Electrical conductivity was described by the small polaron hopping conductivity model, as well as, increases due to regular increments of Sr content for all compositions. Electrical conductivity was measured at 25.2, 26.4 and 37.1Scm-1 for x = 0.10, 0.30 and 0.50, respectively at 800°C.

STUDY OF ELECTRICAL TRANSPORT AND AC SUSCEPTIBILITY IN LaMn1-xCuxO3

2005 ◽  
Vol 19 (06) ◽  
pp. 317-330 ◽  
Author(s):  
MANORANJAN KAR ◽  
S. RAVI
Keyword(s):  
Transition Temperature ◽  
Electrical Transport ◽  
Small Polaron ◽  
Ac Susceptibility ◽  
Ferromagnetic Transition ◽  
X Ray Diffraction ◽  
Polaron Hopping ◽  
Phase Form ◽  
Resistivity Data ◽  
Diffraction Patterns

LaMn 1-x Cu x O 3 compounds have been prepared in single phase form for x = 0 to 0.30. X-ray diffraction patterns recorded at room temperature could be mostly refined using Pbnm space group. Paramagnetic-to-ferromagnetic transitions have been observed up to x = 0.30, from ac susceptibility measurements. Metal–insulator transition in the vicinity of ferromagnetic transition temperature has been observed for x = 0.05 and the resistivity data in the metallic region could be explained in terms of electron–electron and electron–magnon scattering mechanisms. Further increase in Cu-doping beyond x = 0.05 leads to systematic decrease in ferromagnetic transition temperature and ultimately ferromagnetism is destroyed for x = 0.40. The resistivity data of all samples except x = 0.05 exhibit semiconducting behaviors and they could be mostly explained using the adiabatic small polaron hopping model.

scholarly journals DC electrical conduction in strontium vanadium borate glasses

2020 ◽  
Vol 38 (2) ◽  
pp. 359-366
Author(s):  
Arunkumar V. Banagar ◽  
M. Prashant Kumar ◽  
N. Nagaraja ◽  
Anand Tipperudra ◽  
Sangamesh Jakati
Keyword(s):  
Electrical Conductivity ◽  
Molar Volume ◽  
Small Polaron ◽  
Glass Network ◽  
Effective Dielectric Constant ◽  
Total Conductivity ◽  
Borate Glasses ◽  
Polaron Hopping ◽  
Small Polaron Hopping ◽  
Dc Electrical Conductivity

AbstractA series of borate glasses with the composition x(SrO)·(50 – x)V2O5·0.5(B2O3) where x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by melt-quenching technique. The non-crystalline nature of the glasses has been established by XRD studies. Room temperature density and DC electrical conductivity of the samples were investigated in the temperature range of 300 K to 443 K. The molar volume and oxygen packing density (OPD) were estimated. The results show that the density, molar volume and OPD decrease with the increasing of SrO mole fraction. The DC electrical conductivity data has been analyzed in the light of Mott’s small polaron hopping (SPH) model and the activation energies were estimated. The conductivity was observed to rapidly fall and activation energy was found to increase when SrO was incorporated into the glass network. This may indicate that Sr+ ions have not contributed to the total conductivity and the observed conductivity may be of polaronic type only, which is due to the hopping of electrons between multivalent states of vanadium. Various small polaron hopping parameters such as small polaron radius, rp, effective dielectric constant, ϵp, polaron band width, J, optical phonon frequency, υo, small polaron coupling constant, γp, density of states at Fermi level, N(EF) were estimated and discussed.

Enhanced Magnetic and DC Electrical Properties of Sm-Doped Bi2Fe4O9 Nanoplates Synthesized by Sol–Gel Method

NANO ◽  
2020 ◽  
Vol 15 (02) ◽  
pp. 2050020 ◽  
Author(s):  
E. M. M. Ibrahim ◽  
G. Farghal ◽  
Mai M. Khalaf ◽  
Hany M. Abd El-Lateef
Keyword(s):  
Magnetic Measurements ◽  
Small Polaron ◽  
Sol Gel ◽  
Electric Transport ◽  
X Ray Diffraction ◽  
Polaron Hopping ◽  
Gel Method ◽  
Sol Gel Method ◽  
High Temperature Measurement ◽  
Ferromagnetic Ordering

In this work, Bi[Formula: see text]SmxFe4O9 ([Formula: see text], 0.02, 0.06, 0.08, 0.1) nanoplates with an average thickness of 62–125[Formula: see text]nm were synthesized using a sol–gel method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The magnetic measurements show that the nanoplates have weak ferromagnetic ordering. The saturation magnetization of the nanoplates increases as the Sm content increases. The DC electric transport properties were studied by measuring the temperature dependence of the resistivity in the temperature range 300–680[Formula: see text]K. The materials show typical semiconductor features, and the conduction mechanisms are governed by electron and small polaron hopping in the low and high temperature measurement ranges, respectively. The Sm doping results in a significant enhancement in the electrical conductivity of the Bi2Fe4O9 nanoplates.

Thermoelectric Performance of Glass Microsphere Dispersed Bi-Sb Composites at Low Temperature

2013 ◽  
Vol 743-744 ◽  
pp. 120-125
Author(s):  
Zhen Chen ◽  
Ye Mao Han ◽  
Min Zhou ◽  
Rong Jin Huang ◽  
Yuan Zhou ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Materials ◽  
Sem Analysis ◽  
Glass Microsphere ◽  
Thermoelectric Performance ◽  
X Ray Diffraction ◽  
X Ray ◽  
Measurement Results

In the present study, the glass microsphere dispersed Bi-Sb thermoelectric materials have been fabricated through mechanical alloying followed by pressureless sintering. The phase composition and the microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the temperature range of 77~300 K. The ZT values were calculated according to the measurement results. The results showed that the electrical conductivity, Seebeck coefficient and thermal conductivity decreased by adding glass microsphere into Bi-Sb thermoelectric materials. However, the optimum ZT value of 0.24 was obtained at 260 K, which was increased 10% than that of the Bi-Sb matrix. So it is confirmed that the thermoelectric performance of Bi-Sb-based materials can be improved by adding moderate glass microspheres.

Structural and electrical properties of Cu-doped Ni–Zn nanocrystalline ferrites for MLCI applications

2017 ◽  
Vol 31 (33) ◽  
pp. 1750318 ◽  
Author(s):  
D. Venkatesh ◽  
K. V. Ramesh
Keyword(s):  
Electrical Properties ◽  
Cation Distribution ◽  
Tetrahedral Site ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Sem Images ◽  
X Ray ◽  
Structural And Electrical Properties ◽  
Phase Spinel ◽  
Diffraction Patterns

Polycrystalline Cu substituted Ni–Zn ferrites with chemical composition Ni[Formula: see text]Zn[Formula: see text]-Cu[Formula: see text]Fe2O4 (x = 0.00 to 0.25 in steps of 0.05) have been prepared by citrate gel autocombustion method. The samples for electrical properties have been sintered at 900[Formula: see text]C for 4 h. The X-ray diffraction patterns of all samples indicate the formation of single phase spinel cubic structure. The value of lattice parameter is decreases with increasing Cu concentration. The estimated cation distribution can be derived from X-ray diffraction intensity calculations and IR spectra. The tetrahedral and octahedral bond lengths, bond angles, cation–cation and cation–anion distances were calculated by using experimental lattice parameter and oxygen positional parameters. It is observed that Cu ions are distributed in octahedral site and subsequently Ni and Fe ions in tetrahedral site. The grain size of all samples has been calculated by Scanning Electron Microscopy (SEM) images. The variations in DC electrical resistivity and dielectric constant have been explained on the basis of proposed cation distribution.

STRUCTURE AND ELECTRICAL PROPERTIES OF SrO-BOROVANADATE (V2O5)z(SrO)0.2(B2O3)0.8-z GLASSES

2010 ◽  
Vol 24 (11) ◽  
pp. 1471-1488
Author(s):  
A. MEKKI ◽  
G. D. KHATTAK ◽  
M. N. SIDDIQUI
Keyword(s):  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Inductively Coupled Plasma ◽  
Glass Structure ◽  
Model Parameters ◽  
Nominal Composition ◽  
Polaron Hopping ◽  
X Ray ◽  
Dc Electrical Conductivity ◽  
Hopping Model

SrO -borovanadate glasses with the nominal composition (V 2 O 5 ) z( SrO )0.2 ( B2 O 3 ) 0.8-z, 0.4≤z ≤0.8 were studied by direct current (DC) electrical conductivity, inductively coupled plasma (ICP) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and X-ray-powder-diffraction (XRD). These glasses were prepared by a normal quench technique and the actual compositions of the glasses were determined by ICP spectroscopy. XRD patterns confirm the amorphous nature of the present glasses. The temperature dependence of DC electrical conductivity of these glasses has been studied in terms of different hopping models. The IR results agree with previous investigations on similar glasses and it has been concluded that similar to SrO -vanadate glasses, metavandate chainlike structures of SrV 2 O 6 and individual VO 4 units also occur in these SrO -borovanadate glasses. The SrV 2 O 6 and VO n polyhedra predominate in the low B 2 O 3 containing SrO -borovanadate glasses as the B substitutes into the V sites of the various VO n polyhedra and only when the B 2 O 3 concentration exceeds the SrO content do BO n structures appear. This qualitative picture of three distinct structural groupings for the Sr -vanadate and Sr -borovanadate glasses is consistent with the proposed glass structure on previous IR and extended X-ray absorption fine structure (EXAFS) studies on these types of glasses. The conductivity results were analyzed with reference to theoretical models existing in the literature and the analysis shows that the conductivity data are consistent with Mott's nearest neighbor hopping model. However, both Mott VRH and Greaves models are suitable to explain the data. Schnakenberg's generalized polaron hopping model is also consistent with the temperature dependence of the activation energy, but the various model parameters such as density of states, hopping energy obtained from the best fits were found to be not in accordance with the prediction of the Mott model.

CRYSTAL STRUCTURE, ELECTRICAL CONDUCTIVITY AND THERMAL EXPANSION OF Pr1-xSrxFeO3-δ(0 ≤ x ≤ 0.6)

2012 ◽  
Vol 26 (32) ◽  
pp. 1250174 ◽  
Author(s):  
V. PRASHANTH KUMAR ◽  
Y. S. REDDY ◽  
P. KISTAIAH ◽  
C. VISHNUVARDHAN REDDY
Keyword(s):  
Crystal Structure ◽  
Electrical Conductivity ◽  
Thermal Expansion ◽  
Room Temperature ◽  
Small Polaron ◽  
Linear Thermal Expansion ◽  
Lattice Parameter ◽  
Polaron Hopping ◽  
X Ray ◽  
Perovskite Type

The crystal structure at room temperature (RT), thermal expansion from RT to 1000°C and electrical conductivity, from RT to 600°C, of the perovskite-type oxides in the system Pr 1-x Sr x FeO 3(x = 0, 0.2, 0.4, 0.6) were studied. All the compounds have the orthorhombic perovskite GdFeO 3-type structure with space group Pbnm. The lattice parameters were determined by X-ray powder diffraction. The Pseudo cubic lattice parameter decreases with an increase in x, while the coefficient of linear thermal expansion increases. The thermal expansion is almost linear for x = 0 and 0.2. The electrical conductivity increases with increasing x while the activation energy decreases. The electrical conductivity can be described by the small polaron hopping conductivity model.

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