Ferroelastic phase transition in BiVO4: V. Temperature dependence of Bi3+displacement and spontaneous strains

Abstract

For pt.IV see ibid., vol.16, p.5119 (1983). Measurements of the Bi³⁺displacement and the primary and secondary spontaneous strains in the ferroelastic material BiVO₄have been made as a function of temperature by single-crystal X-ray diffraction. The results are discussed using both macroscopic and microscopic mean-field theories of the ferroelastic phase transition. Measurements of the temperature dependence of the optical absorption edge have also been made, which show that the band-gap in BiVO₄varies markedly with temperature. A method for the analysis of structural distortions in ferroelastics based on bond-length/bond-strength relationships is described. A discussion of the structural mechanism of the phase transition in BiVO₄is presented, indicating that the lone-electron pair on the Bi³⁺ion plays a prominent role.