Semiconducting Molybdenum Pyrochlores for high Temperature Applications

1998 ◽  
Vol 512 ◽  
Author(s):  
V. Ponnambalam ◽  
U. V. Varadaraju
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
High Temperature ◽  
Low Temperature ◽  
Solid Solutions ◽  
Power Factor ◽  
Charge Carriers ◽  
Temperature Range ◽  
Maximum Power Factor ◽  
Increasing Temperature

ABSTRACTThe solid solutions (Y1-xYbx)2Mo2O7 were prepared and the systematic changes in the electrical resistivity (ρ=l/σ), thermopower (S) and power factor (S2σ) have been studied in the temperature range 300–900 K. The lattice parameters ‘a’ and ‘c’ are smaller for higher Yb3+ content phases due to smaller Yb3+ radius and a small tetragonality is observed for all the phases. Semiconducting behaviour is seen for all compositions with systematic increase in activation energy with increasing Yb content. All compositions show negative thermopower indicating electrons are the majority charge carriers in the temperature range of measurements. The calculated power factor values S2σ increase with increasing temperature in the low temperature region and a maximum power factor of ∼0.76×10−7 Wcm−1K−2 is observed at 650K.

Influence of Eu Substitution for Y on the High Temperature Electric Transport Properties of YBaCo4O7+δ

2013 ◽  
Vol 724-725 ◽  
pp. 1029-1032 ◽  
Author(s):  
Qing Lin He ◽  
Feng Gao ◽  
Hong Zhang Song ◽  
Xing Hu
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
High Temperature ◽  
Transport Properties ◽  
Power Factor ◽  
Electric Resistivity ◽  
Electric Transport ◽  
Seebeck Coefficients ◽  
Higher Power ◽  
Unmodified Sample

The electric resistivity, Seebeck coefficients and power factors of Y1-xEuxBaCo4O7+δ(x = 0.0, 0.05, 0.1, 0.2) ceramics were investigated from 400K to 1000K. The results show that the presence of Eu decreases electrical resistivity, and has little effect on Seebeck coefficients of the samples. The activation energy of conductivity is calculated by the Arrhenius plots in the semiconductive region. According to power factors, the optimum Eu substitution amount is x = 0.1, which results in a higher power factor of 67.5 μWm-1K-2at 1000K, 30% higher than unmodified sample YBaCo4O7+δ.

scholarly journals SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF SOLID SOLUTIONS OF THE SYSTEM PbF2–NdF3–SnF2

2020 ◽  
Vol 86 (5) ◽  
pp. 24-37
Author(s):  
Pohorenko Yuliia ◽  
Omel’chuk Anatoliy ◽  
Nagornyi Anton
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Solid Solutions ◽  
Basic Structure ◽  
Elementary Cell ◽  
Initial Structure ◽  
Temperature Range ◽  
The Individual ◽  
Increasing Temperature ◽  
Transfer Numbers

In the system PbF2–NdF3–SnF2 are formed solid solutions of the heterovalent substitution Pb0,86-хNdхSn1,14F4+х (0 < x ≤ 0,17) with structure of β–PbSnF4. At x > 0,17 on the X-ray diffractograms, in addition to the basic structure, additional peaks are recorded to the reflexes of the individual NdF3. For single-phase solid solutions, the calculated parameters of the crystal lattice are satisfactorily described by the Vegard rule. The introduction of ions of Nd3+ into the initial structure leads to an increase in the parameter с of the elementary cell from 51.267 Å for x = 0,03 to 51.577 Å for x = 0.17. The replacement of a part of leads ions to neodymium ions an increase in electrical conductivity compared with Pb0.86Sn1.14F4. The slight replacement (3.0 mol. %) of Pb2+ ions by Nd3+ in the structure of Pb0.86Sn1.14F4 causes an increase in the electrical conductivity at T> 530 K (6.88·10-2 S/cm compared to 2.41·10-2 S/cm for the initial sample compound Pb0.86Sn1.14F4). In the region of lower temperatures, the electrical conductivity of the samples of this composition decreases, and below that temperature, on the contrary, slightly reduces the electrical conductivity, approaching the values characteristic of β-PbSnF4. The activation energy of the conductivity thus increases over the entire temperature range. A further increase in the concentration of Nd3+ ions in the synthesized samples causes an increase in their fluoride-ion conductivity throughout the temperature range. It should be noted that samples with a content of 10-15 mol% NdF3 at T>500 K have comparable conductivity values. At lower temperatures, the higher the conductivity, the higher the concentration of the substituent. The highest conductivity and the lowest activation energy have the sample Pb0.69Nd0.17Sn1.14F4.17 (σ373=3.68·10-2 S/сm, Ea=0,1 eV). The fluorine anions in synthesized phases are in three structurally-equivalent positions. The charge transfer is provided by the highly mobile interstitial fluorine anions, whose concentration increases with increasing temperature and concentration of NdF3. The transfer numbers for fluorine anions are not less than 0.99, practically independent of the concentration of neodymium trifluoride.

Damping Capacity of Fe-Ga Alloys

2011 ◽  
Vol 228-229 ◽  
pp. 937-941 ◽  
Author(s):  
Fang Mei Ling ◽  
Jie Zhu ◽  
Li Ji Heng ◽  
Gao Xue Xu
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Damping Capacity ◽  
Torsion Pendulum ◽  
Temperature Peak ◽  
Temperature Range ◽  
Computer Controlled ◽  
Increasing Temperature

The damping capacity of Fe-Ga rods and sheets has been studied using a computer-controlled automatic inverted torsion pendulum instruments in a wide temperature range in a series of frequency. The frequency and temperature has different influence on the damping capacity of solidified Fe83Ga17 rods and (Fe83Ga17)97.25Cr2B0.75 sheets. The damping capacity of all specimens increased with frequencies. The solidified Fe-Ga rods showed an obvious low-temperature peak and a potential high-temperature peak with increasing temperature. However, the damping capacity of Fe-Ga sheets kept steady in a wide temperature range and then rapidly increased on further heating above 400°C. Damping capacity of about 0.02 was obtained in both Fe-Ga rods and sheets at temperatures from room temperature to 500°C. Thus, The Fe-Ga alloys are considered to be a class of promising high damping alloys.

Activation Energy for Recrystallization in Fe-3wt.%Si Alloys with Different S Contents

2013 ◽  
Vol 753 ◽  
pp. 181-184 ◽  
Author(s):  
Wei Min Mao ◽  
Mao Hua Zhang ◽  
Ping Yang ◽  
Kai Ping Wang
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Low Temperature ◽  
Boundary Migration ◽  
Mechanical Calculation ◽  
High Temperature Range ◽  
Temperature Range ◽  
Cottrell Atmosphere

The recrystallization behaviors of 60% rolled Fe-wt.3%Si and Fe- wt.3%Si-Mn-S alloys containing coarsen MnS particles were observed in temperature range 600°C~1000°C. The activation energy for recrystallization was determined according to an Arrhenius type of relationship. It was found that the activation energy in the temperature range 600°C~750°C was much higher than that in the temperature range 850°C~1000°C. Thermo-mechanical calculation indicates that there are hardly precipitation behaviors of MnS particles in 600°C~1000°C. Fe3C will precipitate below 650°C and Cottrell atmosphere will form just above 650°C, which induces dragging effect against the boundary migration during recrystallization and increase the activation energy. The activation energy determined was about 99kJ/mol or 217kJ/mol in Fe-3%Si alloy and 91kJ/mol or 220kJ/mol in Fe-3%Si-Mn-S alloy for the recrystallization in high temperature range of 850°C~1000°C or low temperature range of 600°C~750°C respectively.

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

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.

Electrical Resistivity Anomalies in SbxVyMozOt Phases

2011 ◽  
Vol 170 ◽  
pp. 5-8 ◽  
Author(s):  
Tadeusz Groń ◽  
E. Filipek ◽  
Henryk Duda ◽  
S. Mazur ◽  
K. Bärner
Keyword(s):  
Electrical Resistivity ◽  
General Formula ◽  
Solid Solutions ◽  
Type Conductivity ◽  
Temperature Range ◽  
Small Polarons

Electrical resistivity dips in the temperature range 269-287 K and n-type conductivity below 415 K for solid solutions of MoO3 in SbVO5 with general formula SbxVyMozOt are observed. The electrical resistivity anomalies are interpreted as due to conduction of small-polarons, generated here as electrons together with distortions of their associated defective oxygen lattice and/or alternatively based on the crossover of electronic or polaronic states.

Basic Experiment on Lithium Removal Technique

2012 ◽  
Author(s):  
Tomohiro Furukawa ◽  
Yasushi Hirakawa
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Dissolution Rate ◽  
Chemical Reaction ◽  
Pure Water ◽  
Preliminary Investigation ◽  
Testing Temperature ◽  
Temperature Range ◽  
Removal Technique ◽  
Good Agreement

As a preliminary investigation into the establishment of a lithium removal technique for the components used at the International Fusion Materials Irradiation Facility (IFMIF), experiments were performed on the dissolution of lithium in three solvents: ethanol, pure water, and ethanol–water. In these experiments, hemispherical lithium was immersed in the solvents at constant temperatures, and the degree of dissolution was measured continuously from the height of the sample. From the obtained data, the average dissolution rate in the solvents at each testing temperature (10–90 °C) and the amount of hydrogen generated by the chemical reaction were calculated. The average dissolution rates in ethanol, pure water, and ethanol–water at 30 °C were 0.01, 1.6, and 0.43 mm/min, respectively. Although the average dissolution rate increased with the testing temperature in the low-temperature range (10–50 °C) for all solvents, this increase was saturated in the high-temperature range (50–90 °C) in experiments with pure water and ethanol–water as solvents. The volume of gas collected during each experiment was in good agreement with the volume of hydrogen assumed to be generated from the chemical reaction of lithium with the solvents.

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