Ferroelastic phase transition of bivo4studied by51v nmr

Abstract

Nuclear magnetic resonance (NMR) of ⁵¹V in the ferroelastic BiVO₄ single crystals has been investigated at a fixed frequency of 6 MHz up to 533 K just above its Curie temperature, T_c = 528 K. The seven resonance lines of ⁵¹V(I = 7/2) due to the quadrupole interaction were measured in the three mutually perpendicular crystal planes. While the quadrupole coupling constant (e²qQ/h) is found to be staying nearly the same, whereas the asymmetry parameter (η) is decreased with the increasing temperature. Above T_c, e²qQ/h = 5.031 MHz, and η = 0 were obtained at T = 533 K and the principal Z axis of the electric field gradient tensor is along the crystallographic b axis, same as in the ferroelastic phase. These results are consistent with the phase transition from the monoclinic ferroelastic phase below T_c to the tetragonal paraelastic phase above T_c .