High pressure solid state chemistry of A3(VO4)2 compounds (A: Ca, Sr, Ba)

The purpose of this study is to explore the potential of high pressure methods for preparation of new series of compounds in the A(3)(VO4)(2) systems (A: Ca, Sr, Ba). In this study, we present our in situ vibrational and X-ray diffraction data on the behavior of the A(3)(VO4)(2) compounds at high pressure and room temperature. Upon compression up to 290 kbar, there is no phase change in Ba-3(VO4)(2) Sr-3(VO4)(2) undergoes a first order phase transition to an olivine-like structure at about 150 kbar. In both the ambient pressure and olivine structures of Sr-3(VO4)(2), oxygen atoms form a hexagonal close packing. The packing in the olivine structure is distorted from this due to loss of 3-fold axis. Ca-3(VO4)(2) amorphizes at about 100 kbar. The high pressure behavior of the compounds studied here is related to the size of the A((2))(2+) cations. Small Ca-(2)(2+) cations hinder the completion of crystal-to-crystal transformations in Ca-3(VO4)(2).