Theoretical investigation of mechanical and thermal properties of MPO4 (M = Al, Ga)

Minimum lattice thermal conductivities and mechanical properties of polymorphous MPO4 (M = Al, Ga) are investigated by first principles calculations. The theoretical minimum thermal conductivities are found to be 1.02 W (m K)−1 for α-AlPO4, 1.20 W (m K)−1 for β-AlPO4, 0.87 W (m K)−1 for α-GaPO4 and 0.88 W (m K)−1 for β-GaPO4. The lower thermal conductivities in comparison to YSZ can be attributed to the lattice phonon scattering due to the framework of heterogeneous bonds. In addition, the low shear-to-bulk modulus ratio for both β-AlPO4 (0.38) and β-GaPO4 (0.30) is observed. Our results suggest their applications as light-weight thermal insulator and damage-tolerant/machinable ceramics.