Structural, thermodynamic, and mechanical properties of bulk La and A-La₂O₃

Highlights: • GGA is more realistic to reflect properties of La and La₂O₃ than LDA. • Elastic anisotropy causes big anisotropy of thermal expansion of A-La₂O₃. • Elastic properties of La₂O₃ decease linearly with increase of temperature. • Covalent bonding of La₂O₃ is enhanced with the decrease of temperature. • Calculated results are in good agreement with experimental observations. - Abstract: First principles calculations are combined with the quasi-harmonic approximation and thermal electronic excitation, to have a systematic study of structural, thermodynamic (C_V, C_P, and α_L), and mechanical (C_ij, B, G, and E) properties of bulk La and A-La₂O₃. It is found that the generalized gradient approximation gives a much better reflection of the ground state properties than local density approximation, and that a very strong covalent bonding is formed in A-La₂O₃, mainly due to the pronounced hybridization between O 2p and La 5d as well as 5p states. Calculations also reveal that the electronic contribution to heat capacity of fcc La should be bigger than that of dhcp La, and that elastic anisotropy of A-La₂O₃ would cause the big difference of thermal expansion along the a and c axes. Moreover, the elastic properties of La and A-La₂O₃ decease almost linearly with the increase of temperature, and the descending sequence of bulk moduli is E → B → G within the entire temperature range. The strong covalent bonding of A-La₂O₃ would be enhanced (reduced) with the decrease (increase) of temperature, and the calculated results are in good agreement with experimental observations in the literature