Temperature dependence on phase evolution in the BaTiO3 polytypes studied using ab initio calculations

Identifying the forces that drive a temperature‐induced phase transition is always challenging in the prospect of the first‐principles methods. Herein, we perform a first‐principles study of the temperature effects on structural, energetic, electronic, and vibrational properties of four BaTiO3 polymorphs using quasi‐harmonic approximations. Study of the stability between these four phases, which we break into contributions arising from the vibration of the lattice, electronic structure, and volume expansion/contraction, is helpful to confirm the sequence of phase transitions as cubic → tetragonal → orthorhombic → rhombohedral, as well as its transition temperatures. A general mechanism was proposed based on the combination between structural distortions at [TiO6] clusters, vibrational characteristics, and electronic structure. These findings confirm the power of quasi‐harmonic approximations to disclose the main fingerprints associated with both thermic and mechanical phase transitions, serving as a guide for further theoretical studies. Phase transitions in BaTiO3 single crystals are very interesting due to the structural distortions, which enable the connection between the polymorphs. First‐principles calculations are appropriate to tackle such problem, but they are commonly restricted to studying the electronic structure at 0 K. In this context, the quasi‐harmonic approximation provides an interesting and alternative tool to compute quasi‐harmonic thermal properties of solids beyond the harmonic approximation.