Combined first-principles and EXAFS study of structural instability in BaZrO3

Abstract

Phonon spectrum of cubic barium zirconate is calculated from first principles using the density functional theory. Unstable phonon mode with the [Formula: see text] symmetry in the phonon spectrum indicates an instability of the cubic structure with respect to rotations of the oxygen octahedra. It is shown that the ground-state structure of the crystal is [Formula: see text]. In order to find the manifestations of the predicted instability, EXAFS measurements at the Ba [Formula: see text]-edge are used to study the local structure of [Formula: see text] at 300 K. An enhanced value of the Debye–Waller factor for the Ba–O atomic pair ([Formula: see text]) revealed in the experiment is associated with the predicted structural instability. The average amplitude of the thermal rotations estimated from the measured [Formula: see text] value is [Formula: see text] at 300 K. The closeness of the calculated energies of different distorted phases resulting from the condensation of the [Formula: see text] mode suggests a possible formation of a quenched rotational disorder in [Formula: see text] at low temperature, which can explain the discrepancy between the calculations and experiment.