First‐principles study of thermophysical properties of polymorphous YTaO4 ceramics.

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 (I41/a), and a comprehensive understanding of their thermophysical properties is required. In this study, the thermal and mechanical properties of polymorphous yttrium tantalate (YTaO4) 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 Å3 to 12.95 Å3 per atom, whereas the T to M is 12.95 Å3 to 12.84 Å3 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 YTaO4 is about 11.13 × 10−6 K−1, which is smaller than T YTaO4 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 YTaO4, but also provides support for the design and application of TBC systems. [ABSTRACT FROM AUTHOR]