Ab initio structural and energetic study of LaMO3LaMO3 (M=AlM=Al, Ga) perovskites

The equilibrium crystal structure parameters and the total energies of the polymorphous LaMO3LaMO3 perovskites (M=AlM=Al, Ga) and their constituent binary oxides A-La2O3La2O3, αα-Al2O3Al2O3 and ββ-Ga2O3Ga2O3 were calculated with ab initio method based on density function theory (DFT) and projector augmented wave method (PAW) using both local density approximation (LDA) and generalized gradient approximation (GGA). The relative lattice stabilities of the various configurations with respect to the ground state and the enthalpies of formation of the stable perovskites from the constituent binary oxides were obtained. The enthalpies of formation at 298.15 K calculated within LDA, -67.19-67.19 and -49.99kJmol-1 for the stable configurations of LaAlO3LaAlO3 and LaGaO3LaGaO3, respectively, agree well with the available experimental data, while the enthalpies calculated within GGA are much less negative. It was the first time that recurred the experimental enthalpies of formation at 298.15 K for the stable configurations of LaAlO3LaAlO3 and LaGaO3LaGaO3 from a fundamental ab initio calculation.