Pressure-induced phase transition in α- and β-BiNbO4

Abstract

BiNbO₄ has attracted a great deal of interest due to its excellent photocatalytic activities. Besides, it possesses rich polymorphism. Here, the structural stability and structural evolution of orthorhombic α- and triclinic β-BiNbO₄ were investigated via in situ X-ray diffraction patterns and Raman spectra up to 46.7 GPa. Upon compression, both BiNbO₄ samples become unstable. α-BiNbO₄ transformed into the monoclinic C2/c structure at 10.3 GPa, while β-BiNbO₄ possessed one P-to-P1 isostructural phase transition around 12.7 GPa, and for the first time the crystal structure of each high pressure phase was identified. Both high pressure structures remained stable without obvious symmetry changes during compression to 46.7 GPa. In addition, both phase transitions were reversible upon decompression. These results provide insights to understand pressure-induced reversible phase transition in ABO₄ compounds with polymorphism.