BaZrO3 perovskite has a tolerance factor close to 1.01 and is considered to have an ideal cubic structure which remains on average cubic down to at least 2 K. The results of first principles calculations are, however, inconclusive, with some authors predicting out-of-phase [ZrO6] octahedra rotations [1] while others predicting a cubic symmetry [2]. Most recently Levin et al. [3] have confirmed the a0a0c– type oxygen octahedral rotations with a coherence length of about 3 nm by total neutron scattering data and electron diffraction. Doping with small amounts of Nb or heating above 80 K causes disappearance of these structural distortions [3]. In contrast, Raman and FIR data on BaZrO3 indicate local low-symmetry distortions that persist beyond 700 K [4].
Early reports on MW dielectric properties of BaZrO3 indicated an unusually low Q-factor. In this presentation, I will address possible reasons of high microwave loss in BaZrO3 ceramics with special focus on low-temperature proton dynamics in this fascinating perovskite.
[1] A. Bilic et al., Ground state structure of BaZrO3: A comparative first-principles study, Phys. Rev. B 79, 174107 (2009).
[2] A. Perrichon et al., Unraveling the ground-state structure of BaZrO3 by neutron scattering experiments and first-principles calculations, Chem. Mat. 32, 2824 (2020).
[3] I. Levin et al., Nanoscale-correlated octahedral rotations in BaZrO3, Phys. Rev. B 104, 214109 (2021).
[4] D. Nuzhnyy et al., Broadband dielectric response of Ba(Zr,Ti)O3 ceramics: From incipient via relaxor and diffuse up to classical ferroelectric behavior, Phys. Rev. B 86, 014106 (2012).
The seminar will be chaired by Stanislav Kamba, Department of Dielectrics.