Revisiting structural phases in some perovskites: The case of BaCeO3

An effective Hamiltonian is developed and used to investigate the different equilibrium phases that $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}₃$ can possess, as a function of temperature. Such atomistic technique predicts that monodomain $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}₃$ 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 $Pm\overline{3}m$ 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 $Pm\overline{3}m$ 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 $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}<sub>3</sub>$ 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.''