High pressure behavior of Sr-3(VO4)(2) and Ba-3(VO4)(2)

We have studied pressure-induced transitions and structural changes in isostructural strontium and barium orthovanadates, Sr-3(VO4)(2) and Ba-3(VO4)(2), via Raman spectroscopy, The spectral changes in Ba-3(VO4)(2) can be interpreted as being due to condensation of VO43- units into edge-or corner-shared octahedra with little or no hysteresis on decompression, For Sr-3 (VO4)(2), there is a pressure-induced first-order phase change at about 150 kbar, with large hysteresis on decompression, which can be rationalized as a transition into a spinelloid series of structures, retaining the tetrahedral coordination of the V atoms. (C) 1997 Academic Press.