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

• 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.

First principles calculations are combined with the quasi-harmonic approximation and thermal electronic excitation, to have a systematic study of structural, thermodynamic (CV, CP, and αL), and mechanical (Cij, 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.