Theoretical Prediction of Elastic Stiffness and Minimum Lattice Thermal Conductivity of Y₃Al₅O₁₂, YAlO₃ and Y₄Al₂O₉

Abstract

Combining Clarke's model with first‐principles calculation of average sound velocity, the minimum lattice thermal conductivities (κmin) of Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM) are predicted to be 1.59, 1.61, and 1.10 W·(m·K)−1, respectively. The weak Y–O polyhedra provide “weak zones” that scattering phonons and lead to the low κmin of ternary Y–Al–O compounds. In addition, the extremely low κmin of YAM is attributed to its higher levels of local disorder of crystal structure and weaker chemical bonding compared with those of YAG and YAP. Inspired by theoretical predictions, dense and phase‐pure YAM is synthesized and the experimental thermal conductivity is only 1.56 W·(m·K)−1at 1273 K. Finally, YAM is highlighted as a potential thermal barrier material for its low thermal conductivities at temperatures from 473 to 1273 K.

Theoretical prediction on mechanical and thermal properties of a promising thermal barrier material: Y4Al2O9

“…As shown in Table 1, the calculated lattice parameters are very close to the theoretical ones calculated by Zhan et al [7], but are smaller than the experimental data [39]. The smaller geometry optimized lattice constants can be understood from the following two aspects.…”

“…At high temperatures, yttrium aluminum garnet (i.e., Y 3 Al 5 O 12 , YAG) is stable with Al 2 O 3 [5], which is the thermally grown oxide formed on Ni-based superalloys. Low thermal conductivity of YAG has been confirmed by Zhan et al [7] very recently. Besides YAG, Y 4 Al 2 O 9 (YAM) is also a stable compound in the Y-Al-O  system [8].…”

“…The second-order elastic constants and the bulk modulus, shear modulus, and Young's modulus were also calculated [7]. Low thermal conductivity and high temperature stability were also confirmed by Zhou et al [9] very recently.…”

“…The melting point of YAM is 2020 ℃, which is higher than that of YAG (1940 ℃). In addition, YAM has a low density of 4.44 g/cm 3 , a relative low Young's modulus of 190 GPa, and a low minimum thermal conductivity of 1.10 W·m 1 ·K 1 [7]. The unique combination of these properties makes YAM a promising TBC material for high temperature applications.…”

“…In our previous work, the minimum thermal conductivity of YAM was predicted and low thermal conductivity was experimentally confirmed [7]. The second-order elastic constants and the bulk modulus, shear modulus, and Young's modulus were also calculated [7].…”