FP-LAPW investigation of mechanical and thermodynamic properties of X sub(2)O (X = Na and K) under pressure and temperature effects

In this paper the ground-state structural, elastic and thermodynamic properties of alkali-metal oxides X sub(2)O (X = Na and K) binary compounds at different pressures and temperatures are investigated by using full-potential augmented plane wave plus local orbitals method (FP-LAPW) within density functional theory, using generalized gradient approximation (GGA). The calculated results are in excellent agreement with the available experimental data and other theoretical results. The thermodynamic properties of Na sub(2)O and K sub(2)O are predicted by using the quasi-harmonic Debye model. The pressure-volume-temperature (P-V-T) relationship, the variations of the bulk modulus B, heat capacity C sub(V) and Cp with pressure P and temperature T, thermal expansion coefficient alpha and Debye temperature are obtained systematically in the ranges of 0-80 GPa and 0-1200 K.