Thermal Conductivity Of Solid Solutions Research Articles

Analysis of heat conductivity mechanisms in PbSnTe solid solutions

In the paper, a theoretical calculation of the coefficient of thermal conductivity of solid solutions of PbSnTe was carried out. The contribution of phonon scattering on substitution atoms to the effect of reducing thermal conductivity has been established. The composition of the PbSnTe solid solution, characterized by the lowest values of the lattice component of the thermal conductivity coefficient klat, was determined. The concentration of intrinsic charge carriers in solid solutions is calculated and their influence on the thermoelectric parameters of the material is shown.

Thermal conductivity of solid solutions of Bi2(Te1-xSex )3 (x = 0-0.07)

Relevance. Solid solutions Bi2 (Te1-xSex )3 are effective materials for an n-leg of thermoelectric cooling devices. Recently, concentration anomalies of properties with a low impurity content were detected in these solid solutions (x ~0.01). It is important to establish whether similar anomalies would be observed on the dependence of thermal conductivity λ from the composition of the solid solution, since λ is one of the parameters that determine the thermoelectric quality factor of the material. Purpose. The purpose of this study was to investigate the concentration dependences of the thermal conductivity of the solid solution of Bi2 (Te1-xSex )3 in the interval x = (0-0.07) to identify concentration anomalies and their possible impact on thermoelectric (TE) efficiency. Methodology. Investigation of temperature dependences of thermal conductivity λ was performed by a dynamic calorimeter. Isotherms of λ for different temperatures in the range T = 175-400 K were built on their basis. Results. On isotherms of λ, there is an interval of abnormal growth λ, which becomes more pronounced when the temperature decreases. The presence of this interval is associated with critical phenomena that accompany the transition of the percolation type from dilute to concentrated solid solutions. Conclusions. The estimation of the thermoelectric figure of merit Z of materials is given. It is shown that the detected growth of λ leads to a decrease in Z in the ranges near the critical (x = 0.01), which should be considered in the practical use of solid solutions of Bi2 (Te1-xSex )3

Phase composition and property evolution of (Yb1−xHox)2Si2O7 solid solution as environmental/thermal barrier coating candidates

RE disilicates are good candidates as environmental/thermal barrier coating for SiCf/SiC composite in harsh gas turbine engines. We designed (Yb1−xHox)2Si2O7 solid solutions and studied mechanical properties, thermal properties, and water vapor resistance. Powders with different compositions were synthesized by pressureless sintering, and bulk samples were prepared by Spark Plasma Sintering (SPS). Polymorphic changes with temperature and composition of the solid solutions were examined. Through doping Ho into Yb2Si2O7, water vapor corrosion resistance is significantly promoted, and thermal expansion coefficient is maintained close to that of Si-based ceramics. Compared with host disilicates, thermal conductivity of solid solutions are decreased, and mechanical properties, including Vickers hardness and fracture toughness, are increased. A two-phase domain is found at (Yb1/2Ho1/2)2Si2O7, and the γ to δ phase transition of Ho2Si2O7 is observed during SPS. Among all samples, γ-(Yb1/3Ho2/3)2Si2O7 possesses superior high temperature stability, and excellent water vapor resistance, indicating its performance as environmental/thermal barrier coating.

Исследование фононной теплопроводности твердых растворов CoSi-CoGe с использованием ab initio динамики решетки

Lattice thermal conductivity of solid solutions based on cobalt monosilicide and monogermanide was studied. Electrical and thermal conductivities of CoSi and solid solutions of CoGe(x)Si(1-x) (x=0.03 and 0.07) were experimentally measured in the temperature range of 80-350K. Phonon spectra and thermal conductivity in CoGe(x)Si(1-x) solid solutions were calculated using ab initio lattice dynamics. The results of calculations are in good agreement with the results of measurements obtained in the present work and with the literature data. It was shown that already at a content of 10–15 at.% of Ge, the lattice thermal conductivity decreases by about a factor of 2 compared with pure cobalt monosilicide, and at a germanium content of about 70 at.%, the decrease can reach 3.5 times.

The study of phonon thermal conductivity of CoSi-CoGe solid solutions using ab initio lattice dynamics

Lattice thermal conductivity of solid solutions based on cobalt monosilicide and monogermanide was studied. Electrical and thermal conductivities of CoSi and solid solutions of CoGexSi1-x (x=0.03 and 0.07) were experimentally measured in the temperature range of 80-350 K. Phonon spectra and thermal conductivity in CoGexSi1-x solid solutions were calculated using ab initio lattice dynamics. The results of calculations are in good agreement with the results of measurements obtained in the present work and with the literature data. It was shown that already at a content of 10-15 at.% of Ge, the lattice thermal conductivity decreases by about a factor of 2 compared with pure cobalt monosilicide, and at a germanium content of about 70 at.%, the decrease can reach 3.5 times. Keywords: lattice thermal conductivity, thermoelectrics, first principle lattice dynamics.

THERMOELECTRIC FIGURE OF MERIT IN (AGSB)1-ХPBХSE2 SINGLE CRYSTALS

This article is devoted to studies the dependence of the thermal conductivity coefficient and thermoelectric figure of merit in (AgSb)1-xPbxSe2 single crystals on their composition. We found that the lattice component provides the main contribution to the thermal conductivity of solid solutions (AgSb)1-xPbxSe2 at x=0-0,4. The electronic thermal conductivity in single crystals with values of x at 0,92-1, becomes close to the lattice component. An increase in the Pb fraction of (AgSb)1-xPbxSe2 in the range from x=0 to x=0,4 leads to a decrease in the thermal conductivity (AgSb)1-xPbxSe2 from 0.56 W / K · m to 0.27 W / K · m, and an increase in x from 0,92 to 1 leads to an increase in the thermal conductivity in the range from 0,45 W / K · m to 1,11 W / K · m. The thermoelectric figure of merit was the highest in all compositions: (AgSb)1-xPbxSe2 at x = 0, 0,1, 0,2 0,92, 1 (ZT≈0,014-0,46). Having a high value of the thermoelectric figure of merit, single crystals of such composition are promising materials for thermoelectric energy generation. The smooth change of thermoelectric properties (AgSb)1-xPbxSe2 with a formation in the content of Pb atoms can find practical use in semiconductor instrumentation, where AgSbSe2 and PbSe materials are used.

Enhancement of thermal properties of ytterbium-cerium oxide by zirconium doping for thermal barrier coatings

ABSTRACTRare-earth cerium oxides (RE2Ce2O7, RE = rare-earth elements) are proposed as promising thermal barrier coatings (TBCs) material due to large thermal expansion coefficient (TEC), phase stability and a comparable thermal cycling life to Yttria-Stabilized Zirconia (YSZ). However, the thermal conductivity of RE2Ce2O7 is relatively higher than that of both YSZ and rare-earth zirconates. Here, we report an effective method of reducing the thermal conductivity of Yb2Ce2O7 by Zr-doping. It is shown that, due to the strong phonon scattering caused by mass and radius differences between Ce4+ and Zr4+ ions, and disorder introduced into structures, the thermal conductivity of solid solutions is remarkably reduced with the increasing of Zr4+ content. Considering the high TEC, the Zr-doped Yb2Ce2O7 solid solutions are believed to be promising candidate materials for TBCs at elevated temperature.

Reduced thermal conductivity of solid solution of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 prepared by atmospheric plasma spray technique

To reduce the thermal conductivity and improve the durability of ZrO2 based materials, coatings from different contents of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 are deposited by atmospheric plasma spray technique. The obtained coatings are characterized by X-ray diffraction, scanning electron microscopy and the thermal diffusivity/conductivity is calculated. Substitutional point defects are created in the coating which improves the phonon scattering thereby influencing the thermal conductivity. Pores and cracks are identified in the microstructure and quantitatively analyzed. Samples with higher concentration of defects provided minimum thermal conductivity which might be due to the enhanced phonon scattering. Among the prepared coatings, samples with 25% of 20% CeO2 + ZrO2 and 75% of 8% Y2O3 + ZrO2 provided minimum thermal conductivity in the temperature range 25–1200 °C. The prepared coatings are compared with the pure 8% Y2O3 + ZrO2 coatings. The solid solution of 20% CeO2 + ZrO2 and 8% Y2O3 + ZrO2 demonstrated lower thermal conductivity than the 8YSZ. The reduced thermal conductivity is attributed to the higher concentration of defects which improve the phonons scattering.

Optimization of the Electronic Band Structure and the Lattice Thermal Conductivity of Solid Solutions According to Simple Calculations: A Canonical Example of the Mg2Si1–x–yGexSny Ternary Solid Solution

The dependence of the electronic band structure of Mg2Si0.3–xGexSn0.7 and Mg2Si0.3GeySn0.7–y (0 ≤ x, and y ≤ 0.05) ternary solid solutions on composition and temperature is explained by a simple linear model, and the lattice thermal conductivity of solid solutions with different Si/Ge/Sn ratios is predicted by the Adachi model. The experimental results show excellent consistency with the calculations, which suggests that the approach might be suitable for describing the electronic band structure and the lattice thermal conductivity of other solid solutions using these simple calculations. Beyond this, it is observed that the immiscible gap in the Mg2Si1–xSnx binary system is narrowed via the introduction of Mg2Ge. Moreover, for the Sb-doped solid solutions Mg2.16(Si0.3GeySn0.7–y)0.98Sb0.02 (0 ≤ y ≤ 0.05), the energy offset between the light conduction band and the heavy conduction band at higher temperatures (500–800 K) will decrease with an increase in Ge content, thus making a contribution to the conduc...

Temperature and concentration dependences of thermal conductivity of solid solutions of gadolinium and dysprosium sulfides

Thermal conductivity of a number of solid solutions of gadolinium and dysprosium sulfides has been studied experimentally within the temperature range 80-400 K. The work offers the data on thermal conductivity coefficient and lattice thermal conductivity of the studied samples. It was found that replacement of gadolinium ions by dysprosium ions leads to significant decrease of the samples’ thermal conductivity and changes its temperature dependence character due to the resonance scattering of phonons by paramagnetic ions of dysprosium. Influence of this mechanism of phonon scattering conditions the area of anomalous change observed on the concentration dependence of thermal conductivity coefficient.

Temperature and pressure dependences of the thermal conductivity of As2(Se1-xTex)3 solid solutions

The effect of temperature and pressure on the thermal conductivity of solid solutions based on the As2(Se1 - xTex)3 system was investigated in glassy and polycrystalline samples at 273–450 K and hydrostatic pressures of up to 0.35 GPa. The compound As2Se3 was studied in a temperature range of 300–760 K. Analysis showed that the short-cange order structure in As2Se3 remains unchanged upon the glass—liquid transition right up to 760 K.

Thermal conductivity of actinide mononitride solid solutions

The thermal conductivities of actinide mononitride solid solutions, (U,Np)N and (Np,Pu)N, were determined from thermal diffusivities measured using the laser flash method from 740 to 1630 K. It was found that the thermal conductivities of the solid solutions have a similar temperature dependence to that of the respective mononitride and decreased from the UN-side to the PuN-side in order, especially in the UN-rich region for (U,Np)N and the NpN-rich region for (Np,Pu)N over the temperature range investigated.

The effect of rare earths on thermal conductivity of uranium, plutonium and their mived ovide fuels

The effect of solid fission products on the thermal conductivity of ovide fuels has been studied systematically by simulating them with their stable isotopes. (U, R)O 2.00 (R ev Nd, Sm, Eu, Gd, Y; RO 1.5 = 0–15 mol.%), (Pu, R')O 2.00 (R' ev Nd, Y; R'O 1.5 ev 0–10 mol.%) and (M, R)O 2.00 ( M = U 0.8 + Pu 0.2 R ev Nd, Eu; RO 1.5 ev 0–10 mol.%) were prepared and thermal conductivities were determined in the temperature range of 700–1900 K from thermal diffusivities measured by a laser flash method. The decreases in the thermal conductivities of solid solutions by adding rare earth elements to the ovide fuels are governed mainly by the lattice defect thermal resistivities. These can be reasonably evplained by the lattice defect model for dielectric solids considering U 4+, U 5+, Pu 4+, Pu 5+, R 3+ or O 2− ions as the phonon scattering centres.

Thermal conductivity of binary disordered continuous solid solutions

A simplified model for the structure and an approximate method of computing the thermal conductivity of continuous solid solutions are proposed. The method is suitable for a check, extension of the measurement results, and prediction of the thermal conductivity of solid solutions.