Effect of iron chloride on the polaronic conduction in potassium phosphateglasses containing iron oxide

2000 ◽  
Vol 78 (12) ◽  
pp. 1091-1105 ◽  
Author(s):  
Y M Moustafa
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Structural Changes ◽  
Small Polaron ◽  
Iron Chloride ◽  
Polaron Hopping ◽  
Exponential Factor ◽  
Order Of Magnitude ◽  
The Difference ◽  
Fe Ions

DC electrical conductivity measurements of Fe2O3–K2O–P2O5 glasses containing iron chloride have been carried out in the temperature range from room temperature to 360°C. The DC conductivity was analyzed in terms of small polaron hopping theory. The hopping regime between Fe ions was confirmed to be nonadiabatic. The increase in the conductivity was of the same order of magnitude as the change in the pre-exponential factor upon increasing the FeCl3 content. The decrease in the activation energy with increasing FeCl3 content was interpreted in terms of a decrease in the distance between the iron sites. The increase in electrical conductivity was ascribed to the difference in the activation energy. The variation in the conductivity parameters was interpreted in terms of the structural changes that take place upon increasing the FeCl3 content of the glasses. PACS No.72.20Ee

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

scholarly journals SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF SOLID SOLUTIONS OF THE SYSTEM RbF-PbF2-SnF2

2019 ◽  
Vol 85 (5) ◽  
pp. 60-68
Author(s):  
Yuliay Pogorenko ◽  
Anatoliy Omel’chuk ◽  
Roman Pshenichny ◽  
Anton Nagornyi
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Solid Solutions ◽  
Basic Structure ◽  
Elementary Cell ◽  
Initial Structure ◽  
Fluoride Ions ◽  
Temperature Range ◽  
Order Of Magnitude

In the system RbF–PbF2–SnF2 are formed solid solutions of the heterovalent substitution RbxPb0,86‑xSn1,14F4-x (0 < x ≤ 0,2) with structure of β–PbSnF4. At x > 0,2 on the X-ray diffractograms, in addition to the basic structure, additional peaks are recorded that do not correspond to the reflexes of the individual fluorides and can indicate the formation of a mixture of solid solutions of different composition. For single-phase solid solutions, the calculated parameters of the crystal lattice are satisfactorily described by the Vegard rule. The introduction of ions of Rb+ into the initial structure leads to an increase in the parameter a of the elementary cell from 5.967 for x = 0 to 5.970 for x = 0.20. The replacement of a part of leads ions to rubium ions an increase in electrical conductivity compared with β–PbSnF4 and Pb0.86Sn1.14F4. Insignificant substitution (up to 3.0 mol%) of ions Pb2+ at Rb+ at T<500 K per order of magnitude reduces the conductivity of the samples obtained, while the nature of its temperature dependence is similar to the temperature dependence of the conductivity of the sample β-PbSnF4. By replacing 5 mol. % of ions with Pb2+ on Rb+, the fluoride ion conductivity at T> 450 K is higher than the conductivity of the initial sample Pb0,86Sn1,14F4 and at temperatures below 450 K by an order of magnitude smaller. With further increase in the content of RbF the electrical conductivity of the samples increases throughout the temperature range, reaching the maximum values at x≥0.15 (σ573 = 0.34–0.41 S/cm, Ea = 0.16 eV and σ373 = (5.34–8.16)•10-2 S/cm, Ea = 0.48–0.51 eV, respectively). In the general case, the replacement of a part of the ions of Pb2+ with Rb+ to an increase in the electrical conductivity of the samples throughout the temperature range. The activation energy of conductivity with an increase in the content of RbF in the low-temperature region in the general case increases, and at temperatures above 400 K is inversely proportional decreasing. The nature of the dependence of the activation energy on the concentration of the heterovalent substituent and its value indicate that the conductivity of the samples obtained increases with an increase in the vacancies of fluoride ions in the structure of the solid solutions.

Influence of Sm3+ doping on microstructure and electrical properties of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7

2015 ◽  
Vol 08 (03) ◽  
pp. 1540012 ◽  
Author(s):  
Jia-Hu Ouyang ◽  
Cheng Zhu ◽  
Zhan-Guo Liu ◽  
Zhe Ren ◽  
Lin Jing
Keyword(s):  
Electrical Conductivity ◽  
Short Range ◽  
Mixed Crystal ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Ac Impedance Spectroscopy ◽  
Exponential Factor ◽  
Structure Changes ◽  
Pyrochlore Type ◽  
The Difference

( Nd 0.7 Yb 0.3)2 Zr 2 O 7 and (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 (0 < x ≤ 0.25) ceramics have been synthesized by pressureless sintering by tailoring the chemical compositions. Microstructure and electrical conductivity of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and AC impedance spectroscopy. ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 ceramic exhibits a mixed crystal structure of defect fluorite and pyrochlore. After doping with Sm 3+ cations, the structure changes from a mixed type of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 to a single pyrochlore type of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7, as the addition of Sm 3+ reduces the difference in ionic radius between Nd 3+ and Yb 3+. However, (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 ceramics contain the localized short-range disorder despite the structural order overall in the pyrochlore. The measured total conductivities of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 obey the Arrhenius relation. Doping of Sm 3+ enhances the electrical conductivity of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 ceramic significantly, which is closely related to the variations in the concentration of oxygen vacancies at 48f sites, relatively low activation energy and high pre-exponential factor caused by the long-range order and short-range disorder.

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.

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 Synthesis and characterization of polyaniline-polyvinyl chloride blends doped with sulfamic acid in aqueous tetrahydrofuran

2006 ◽  
Vol 4 (4) ◽  
Author(s):  
Sadia Ameen ◽  
Vazid Ali ◽  
M. Zulfequar ◽  
M. Mazharul Haq ◽  
Mushahid Husain
Keyword(s):  
Activation Energy ◽  
Structural Changes ◽  
Sulfamic Acid ◽  
Dc Conductivity ◽  
Synthesis And Characterization ◽  
Chemical Doping ◽  
Two Phase ◽  
Fixed Amount ◽  
Exponential Factor

AbstractThe temperature dependence of direct current (dc) conductivity was studied for various samples of polyaniline-polyvinylchloride (PANI-PVC) blended films. Polyaniline was doped with different concentrations of sulfamic acid in aqueous tetrahydrofuran (THF) and the blended films were prepared by varying the amount of doped PANI relative to a fixed amount of PVC. The dc conductivity of PANI-PVC blended films was measured to determine the effect of sulfamic acid (dopant) in the temperature range (300–400K). The mechanism of conduction is explained by a two-phase model. In order to evaluate the effect of the dopant, conductivity-derived parameters such as the pre-exponential factor (σ o) and the activation energy (ΔE) were calculated. The structural changes of polyaniline-PVC blended films were characterized by FTIR spectroscopy that explores information about the suitability of the dopant in the chemical doping process.

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.

Synthesis and Characterization of the Cathode Materials La0.7Sr0.15Ca0.15Co1-yFeyO3-δ for ITSOFC

2010 ◽  
Vol 105-106 ◽  
pp. 653-656
Author(s):  
W.Y. Gao ◽  
Z.Q. Hu ◽  
X.G. Sui ◽  
C.M. Li ◽  
N.L. Tang ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Cathode Materials ◽  
Raw Materials ◽  
Small Polaron ◽  
Polaron Hopping ◽  
Metal Nitrates ◽  
Conducting Mechanism ◽  
A Site ◽  
P Type

La0.7Sr0.15Ca0.15Co1-yFeyO3-δ(LSCCF)powders with 0.2y0.5 for the applications as the cathode materials in intermediate temperature solid oxide fuel cell(ITSOFC) were synthesized by glycine-nitrates-process(GNP) using metal-nitrates and glycine as the raw materials. The process, crystal structure and particles morphology of the powders calcined at 600°C,800°C,1000°C for 3h were characterized by IR,XRD and SEM. The experimental results show that co-doped Ca2+ and Sr2+ replacing some La3+ in A site and Fe3+ replacing some Co3+ in B site didn’t influence the formation of perovskite structure and the powders calcined at 800°C for 3h were high pure single perovskite state. The electrical conductivity of LSCCF samples sintered at 1200°C for 3h,was measured as a function of temperature from 100°C to 800°C by the four-probe DC method in air.As a result, the conducting mechanism of LSCCF is p-type small polaron hopping process, and the electrical conductivity are all higher than 100 S/cm. But the electrical conductivity of LSCCF samples increase with Fe3+ content decrease.

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.

scholarly journals Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

Chemosensors ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 241
Author(s):  
Milena P. Dojcinovic ◽  
Zorka Z. Vasiljevic ◽  
Janez Kovac ◽  
Nenad B. Tadic ◽  
Maria Vesna Nikolic
Keyword(s):  
Activation Energy ◽  
Sodium Alginate ◽  
Room Temperature ◽  
Small Polaron ◽  
Spinel Phase ◽  
Sol Gel ◽  
Complex Impedance ◽  
Relaxation Frequency ◽  
Polaron Hopping ◽  
Ft Ir

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.

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