High pressure structural study on BaZr(PO₄)₂

Rare earth phosphates, BaZr(PO₄)₂ with A = Ca, Sr and Ba are used for chemical separation of nuclear waste. Zr phosphates are good ionic conductors and catalysts and are known to be good inorganic ion exchangers. High pressure can substantially change the structure of materials which in turn will affect their physical properties. BaZr(PO₄)₂ has been studied under high pressure using synchrotron based X-ray diffraction. These measurements show the ambient phase to be stable only up to about 1 GPa. Beyond this pressure several new peaks emerges indicating onset of first order structural transition to a high pressure phase. When the sample is further compressed, another phase transition is observed around 4 GPa. This new phase remains stable up to the highest pressure in the experiments i.e. ∼12 GPa. On release of pressure, the structure slowly reverts back to the first high pressure phase. At complete release of pressure, ambient phase is retained with small fraction of first high pressure phase. (author)