BiVO4 is known as one of the very few examples of a material exhibiting a “proper” ferroelastic transition, where strain is the primary order parameter. This tetragonal-to-monoclinic phase transition has been scrutinized in details in the past, mostly to reveal and confirm this original property [1]. More recently, BiVO4 has regained interest for its optical properties and potential applications to photocatalysis, due to its absorption in the visible range. In this work we re-examine the ferroelastic transition in BiVO4 in the light of its possible antiferroelectric character predicted in [2], and hinted at by its small but distinct dielectric anomaly [3]. We give a detailed description of the phonon spectrum across the transition, as measured by Raman spectroscopy, and discuss mode couplings in a hard-mode spectroscopy approach. From first-principle phonon calculations for the low- and high-symmetry phases, we give a full mode assignment of the phonon modes and vibration patterns, and discuss the behaviour of the low-lying polar and antipolar modes in relation with antiferroelectricity.
References
[1] Cummins and Levanyuk, Light scattering near phase transitions, Elsevier Science (1983).
[2] Tolédano and Guennou, Phys. Rev. B 94, 014107 (2016).
[3] Dudnik et al., Fiz. tverd. tela 16, 2733 (1974).