Response of the physical properties of δ-Y6WO12 and Y6UO12 to pressure

The effect of pressure on the physical properties of δ-phase Y6WO12 and Y6UO12 was investigated by first-principles calculations combining with Quasi-harmonic approximation (QHA). In this work, the relationship between pressure and physical properties of Y6BO12 (B = U and W) has been characterized. The molar Gibbs free energy of Y6BO12 (B = U and W) increases with increasing pressure. By fitting the pressure-dependent Gibbs free energy from 0 to 10 GPa and extrapolating, a series of critical pressures at different temperatures were obtained. The results indicate that Y6WO12 is easier to experience a pressure-induced transformation than Y6UO12. Comparing the performance of δ-phase compound under pressure and irradiation, we found that the compound with higher Frenkel-pair formation energy shows more excellent irradiation-induced amorphization resistance and stability under pressure. For Y6BO12 (B = U and W), the bulk modulus increases with increasing pressure, while the thermal expansion coefficient and specific heat capacity at constant pressure CP decrease with increasing pressure. The specific heat capacity at constant volume CV is not sensitive to pressure. The calculated results demonstrated that the mechanical and thermal properties of Y6UO12 are more susceptible to pressure than those of Y6WO12.