Domain structure and magnetic resonance studies of ferroelastic BiVO4 revisited

Bismuth vanadate (BiVO4) is a ferroelastic material undergoing a reversible second order phase transition at 528 K(T-c) between the tetragonal and monoclinic structure. There have been experimental studies on the incommensurate domain wall (W') which reported different orientation angles. In order to clarify this we have tried to calculate it numerically in terms of lattice constants above and below T-c by employing the theory of Sapriel, and obtained it to be either 35.9 degrees or 54.1 degrees. It also turns out that the shear strain (S-21) in the ferroelastic phase depends on the crystal growing condition. The remaining internal stress appears to be responsible for the formation of W' wall. The host atom nuclear magnetic resonance and the S-state impurity electron magnetic resonance are also reviewed. The nuclear electric quadrupole interaction of V-51 and Bi-209 in BiVO4 was evaluated in terms of the point charge model based on the crystal structure. The result of electric field gradient tensor turns out to be reasonable with experimental values. The zero-field splitting tensor of Mn2+, Fe3+ and Gd3+ are also compared, and the deduced local environment of these ions in the host are confirmed. Finally the second-order phase transition according to the Landau's framework is found in this crystal from the temperature dependence of magnetic resonance parameters.