First-principles Study of Structural, Mechanical and Thermal Properties of RE₂Ti₂O₇ (RE=Gd, Y, Ho, Er)

In this work, we studied the structural, mechanical, and thermal properties of RE₂Ti₂O₇ (RE=Gd, Y, Ho, Er) pyrochlores by the first-principles calculations combining with the quasi-harmonic approximation. Our study reveals that RE₂Ti₂O₇ possess excellent resistance to compression and shear at the ground state. Moreover, these compounds can be approximate to elastically isotropic materials because their Zener ratios are close to 1. The obtained thermal expansion coefficient agrees well with the experimental results at high temperature. The mean thermal expansion coefficient of the RE₂Ti₂O₇ compound is about (10.4~13.1)×10^-6 K^-1 in the temperature range of 500~1 500 K. We also employed Slack's model to estimate thermal conductivity, and the results located in the range of 1.5~4.9 W·m^-1·K^-1 at 1 000 K.