Revisiting structural phases in some perovskites: The case of BaCeO3

An effective Hamiltonian is developed and used to investigate the different equilibrium phases that BaCeO3 can possess, as a function of temperature. Such atomistic technique predicts that monodomain BaCeO3 adopts a phase transition sequence that differs from the one commonly experimentally reported in this specific important perovskite, even if the end members of this sequence (namely, the high-temperature cubic Pm3 over line m state and the orthorhombic Pbnm ground state) are identical between our simulations and measurements. In contrast with this experimental phase transition sequence, the predicted one is, in fact, in line with a rule denoted here as "the gradual tilting rule" that guides the progressive change of oxygen octahedral tiltings about the three Cartesian axes from Pm3 over line m to Pbnm. The fact that this rule is obeyed in many perovskites, along with some of our analyses and previous works, leads us to strongly suggest that intermediate phases experimentally reported in BaCeO3 pertain to multidomains, twinning, and/or antiphase boundaries. Such suggestion should also apply to other perovskites for which the structural phase transition sequence does not follow "the gradual tilting rule."