Theoretical Investigations on the Structural, Electronic, Mechanical, and Thermal Properties of MP2O7 (M = Ti, Hf)

A systematical ab initio analysis on MP2O7 ( M = Ti, Hf) is presented in this work. Density functional theory ( DFT) computations were performed for the electronic, mechanical, and thermal properties of MP2O7. Heterogeneous bonding nature of MP2O7 was revealed by examining the structural and electronic properties, M-O bonds were weaker than P-O bonds. The elastic constants and polycrystalline mechanical properties of MP2O7 were reported. Based on the low shear-modulus-tobulk- modulus ratios and positive Cauchy pressure, MP2O7 ceramics were predicted to be quasi-ductile. In addition, the minimum thermal conductivities were estimated to be 1.52 and 0.99 W.m(-1).K-1 for TiP2O7 and HfP2O7, respectively. The ultra-low thermal conductivities were contributed to the lattice phonon scattering due to the heterogeneous bonding nature. Our theoretical results emphasize the importance of weak M-O bonds in the determination of mechanical and thermal properties of MP2O7.