The domain structure of ferroelastic BiVO₄studied by magnetic resonances

Abstract

The domain structure of the ferroelastic BiVO4 single crystal has been investigated using the nuclear magnetic resonance (NMR) of 51V and by the electron paramagnetic resonance (EPR) of the Mn2+ ions contained in the crystal as an impurity. The 14 resonance lines of 51V (I=7/2) in a BiVO4 crystal with the twin domain were measured in the crystallographic a-b (or c-b) and c-a (or a-c) planes with an FT NMR spectrometer. Two sets of Mn2+ EPR signals were also obtained in the c-a plane. These two sets of NMR and EPR signals originate from the twin-domain structure. From these two sets of experimental data from 51V NMR and Mn2+ EPR, it is confirmed that the BiVO4 single crystal has the prominent (W-plane) domain wall reported previously. The investigated domain structure is found to be stable with time in contrast with a previous report by Baran et al. The previous model of the twinning mechanism derived from NMR and X-ray diffraction data has been improved by employing the EPR results. The observed W plane of the domain wall in BiVO4 can be explained by the ferroelastic species 4/mmm F 2/m instead of 4/m F 2/m.