Recently, in order to develop novel materials with optimized properties, "high entropy" has attracted significant attention in the field of materials research relate to structural entropy within a material. [1][2] Multi-principal high-entropy alloys and ceramics can be synthesized, which exhibit several excellent properties, such as high strength and toughness, corrosion resistance, wear resistance, thermal performance, and electrical performance, on the basis of four high-entropy effects [3][4][5][6] : (1) high-entropy effect of thermodynamics; (2) lattice distortion effect of structure; (3) hysteretic diffusion effect; and (4) cocktail effect on performance.The high-entropy can significantly improve the comprehensive performance of the materials. For example, Gild et al. 7 reported high-entropy fluorite rare-earth oxides, that is, REO 2-δ , with thermal conductivities of 1.1-2.02 W•m -1 •K -1 , therefore, REO 2-δ has shown potential as low-thermal-conductivity materials. Ren et al. 8 synthesized a (Y 1/4 Ho 1/4 Er 1/4 Yb 1/4 ) 2 SiO 5 ceramic with excellent phase stability and low thermal conductivity (1.1 W•m -1 •K -1 at 1300°C), which is considered to be applied as a thermal and environmental barrier coating (TEBC) material. Yan et al. 9 reported a high-entropy ceramic (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )C, which exhibited a much lower thermal conductivity (5.42-6.45 W•m -1 •K -1 at room temperature) than the binary carbides, such as HfC, ZrC, TaC, and TiC(6.3-29.3 W•m -1 •K -1 at room temperature). Zhao et al. 10 reported a new type of rare-earth zirconate (La 0.2 Ce 0.2 Nd 0.2 Sm 0.2 Eu 0.2 ) 2 Zr 2 O 7 high-entropy ceramic with low thermal conductivity (0.76 W -1 •m -1 •k -1 ) and low grain growth speed, which consolidated its potential value in the field of TBCs. Zhao et al. 11 reported (Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2 Yb 0.2 ) 4 Al 2 O 9 exhibits a close thermal expansion coefficient (6.96 × 10 −6 K −1 at 300-1473 K) to that of mullite, good phase stability from 300 to 1473 K, and low thermal conductivity (1.50 W -1 •m -1 •k -1 at room temperature).

The low thermal conductivity (κ) has a significant impact on the application of thermal barrier coatings (TBCs). Rare‐earth tantalates (RETaO4) are one kind of the most promising TBC materials with low thermal conductivity. However, the underlying mechanism of low κ in RETaO4 has remained a mystery. In this work, the thermal transport properties of monoclinic (m)‐RETaO4 (RE = Y, Eu, Gd, Dy, Er) compared with ZrO2 are conducted to reveal the mechanism of low lattice thermal conductivity in the former compounds using highly accurate phonon Boltzmann transport equation combined with first‐principles calculations. The predicted κ is in good agreement with experimental data, which proves that this work is convincing. The result shows that ErTaO4 has the lowest κ (1.37 W m−1 K−1 at 1600 K), which is much lower than ZrO2 (2.49 W m−1 K−1 at 1600 K). It is found that the strong anharmonicity and large scattering rate in m‐RETaO4 are mainly derived from strong ionic bonding in the crystal structure, and strong anti‐crossing property of acoustic‐optical phonon branches in phonon dispersion. Both mechanisms can effectively reduce the phonon group velocity and increase the phonon scattering rates of m‐RETaO4, leading to lower κ than ZrO2. Fortunately, two descriptors, including distortion degree and stretching force constant, are suggested to be used to quickly screen the doping or multicomponent RETaO4 with relatively lower κ, which could also be extended to other potential TBCs systems, that is, rare‐earth silicate, rare‐earth cerate, and so on.

Tailoring the structure and properties of materials using the high-entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare-earth niobates was successfully prepared by a solid-phase reaction method, including (Sm

Yttrium tantalate ceramics with ferroelasticity are potential candidates for thermal barrier coating (TBC) ceramics. During the phase transition process, there are three main phases with monoclinic (I2/a), monoclinic-prime (P2/a), and tetragonal structures (I 41 /a), and a comprehensive understanding of their thermophysical properties is required. In this study, the thermal and mechanical properties of polymorphous yttrium tantalate (YTaO 4 ) ceramics are systematically investigated under finite temperature by performing first-principles calculations combined with quasi-harmonic approximation. The first-principle study results show that the volume change from M' to T phase is 12.85 Å 3 to 12.95 Å 3 per atom, whereas the T to M is 12.95 Å 3 to 12.84 Å 3 per atom, and the change is less than 1%, showing that this process produces almost no volume change.However, the thermal expansion coefficients (TECs) and Young's modulus vary greatly, the TECs value of M YTaO 4 is about 11.13 × 10 −6 K −1 , which is smaller than T YTaO 4 as the value 12.01 × 10 −6 K −1 , and the Young's modulus values of M, M', and T phases are 140. 34, 156.68, and 123.29 GPa, respectively. Lastly, the calculated O-Ta bond is stronger than the O-O and O-Y bonds according to the mean bond population and average bond length, resulting in a higher modulus. This work will not only expand the internal mechanism of the thermophysical properties of YTaO 4 , but also provides support for the design and application of TBC systems.

It is a critical issue to reduce the thermal conductivity and increase the thermal expansion coefficient of ceramic thermal barrier coating (TBC) materials in the course of their utilization. To synthesize samples with different composition and measure their thermal conductivity by the traditional experimental approaches is time-consuming and expensive. Most classic and empirical models work inefficiently and inaccurately when researchers attempt to predict the thermophysical properties of TBC materials. In this research project, we tentatively exploit a Genetic Algorithm-Support Vector Regression (GA-SVR) machine learning model to study the thermophysical properties, illustrated with the potential TBC materials ZrO2 doped DyTaO4, which has resulted in the lowest thermal conductivity in rare earth tantalates RETaO4 system. Meanwhile, we employ statistical parameters of correlation coefficient (R2) and mean square error (MSE) to evaluate the accuracy and reliability of the model. The results reveal that this model has brought about high correlation coefficients of thermal conductivity and thermal expansion coefficient (99.8% and 99.9%, respectively), while the MSE values are 0.00052 and 0.00019, respectively. The doping concentration of ZrO2 was optimized to reach as low as 0.085-0.095, so as to reduce their thermal conductivity further and increase their thermal expansion. This model provides an accurate and reliable option for researchers to design ceramic thermal barrier coating materials.

The adiabatic shear sensitivity of ultra-high-strength steels is closely related to their thermal conductivity. Therefore, it is essential to investigate the effects of alloying elements on the thermal conductivity of ultra-high-strength steel. In this study, the variation in the scattering behavior of electrons with respect to temperature and the mechanism of three-phonon scattering were considered for obtaining the contributions of electrons and phonons, respectively, to the thermal conductivity of alloys while solving the Boltzmann transport equation. By predicting the effect of ten alloying elements on the electronic thermal conductivity (κe), it was found that, at 1200 K, the doping of iron with Ni and Cr endowed iron with κe values of 24.9 and 25.7 W/m K, respectively. In addition, the prediction for the lattice thermal conductivity (κL), which was performed without considering point defect scattering, indicated that elements such as Al, Co, Mn, Mo, V, and Cr demonstrate a positive effect on the lattice thermal conductivity, with values of 3.6, 3.7, 3.0, 3.1, 3.9, and 3.8 W/m K, respectively. The contribution of κL is only 5–15% of the total thermal conductivity (κtotal). The alloying elements exhibited a similar effect on κtotal and κe. Δκi; the change in thermal conductivity with respect to κ0 owing to the alloying element i was evaluated according to the total thermal conductivity. These values were used to understand the effect of the concentration of alloying elements on the thermal conductivity of iron. The Δκi values of Ni, Co, and W were 6.44, 6.80, and 6.06, respectively, indicating a reduction in the thermal conductivity of iron. This paper provides theoretical guidance for the design of ultra-high-strength steels with a high thermal conductivity.

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