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Several experiments conducted over decades have revealed that theperovskite-structured BaCeO3 goes through a series of temperature-inducedstructural phase transitions. However, it has been frequently observed that thenumber of phases and the sequence in which they appear as a function oftemperature differ between experiments. Insofar as neutron diffraction andRaman spectroscopy experiments are concern, four structures are wellcharacterized with three transitions: Pnma to Imma [563 K] to R-3c [673 K] toPm-3m [1173 K]. In contrast, thermoanalytical methods showed multiplesingularities corresponding to at-least three more structural transitions ataround 830 K, 900 K, and 1030 K. In account of these conflicting experimentalfindings, we computed free energy phase diagram for BaCeO3 employing crystalstructure data mining in conjunction with first principles electronic structureand phonon lattice dynamics. A total of 34 polymorphs have been predicted, themost stable of which follows the Glazer classification of the perovskite tiltsystem. It has been predicted that the Cmcm and P4/mbm phases surpass Pnma at666 K and 1210 K, respectively. At any temperature, two alternate tetragonalphases (P42/nmc and I4/mcm) are also found to be 20 to 30 meV less favored thanthe Pnma. While the calculated stability order of the predicted polymorphs isin acceptable agreement with the results of neutron diffraction, thetransitions observed in thermoanalytical studies could be ascribed to thedevelopment of four novel phases (Cmcm, P4/mbm, P42/nmc, and I4/mcm) atintermediate temperatures. However, we analyze that the R-3c phasepredominantly stabilized over a broad temperature field, masking all subsequentphases up until the cubic Pm-3m. Consequently, the novel phases predicted tooccur in thermoanalytical studies are only fleetingly metastable.

Structural phase transitions in perovskite BaCeO3 with data mining and first-principles theoretical calculations