Rare earth phosphates, AZr(PO4)2 with A = Ca, Sr and Ba are used for chemical separation of nuclear waste [1,2]. Zr phosphates are good ionic conductors and catalysts and are known to be good inorganic ion exchangers [3]. BaZr(PO4)2 has been studied under high pressure using synchrotron based powder x-ray diffraction and Raman scattering experiments. High pressure XRD 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 (HP-1). With further compression, another phase transition is observed around 4 GPa (HP-2). This new phase remains stable up to the highest pressure in the experiments i.e. ~12 GPa. At complete release of pressure, ambient phase is retained with small fraction of first high pressure (HP-1) phase. High pressure Raman scattering experiments also show the ambient structure to be stable only upto ~1 GPa. Above this pressure, Raman spectrum shows emergence of many new Raman modes, indicating a structural phase transition (HP-1). Changes in the Raman spectrum are observed at ~3 GPa. This indicates onset of second phase transition. At ~4 GPa, sample completely transforms to the HP-2 phase which remains stable up to the lastt pressure in the experiments i.e. ~16 GPa. When pressure is slowly released, sample transforms to HP-1 phase around ~1 GPa. Sample shows traces of HP-1 phase at complete release of pressure. These observations are in corroboration with high pressure XRD experiments.
References:
[1] K. Popa, R. J. M. Konings, P. Boulet, D. Bouëxière and A. F. Popa, Thermochimica Acta 436 (1), 51-55 (2005).
[2] D. Bregiroux, K. Popa, R. Jardin, P. E. Raison, G. Wallez, M. Quarton, M. Brunelli, C. Ferrero and R. Caciuffo, Journal of Solid State Chemistry 182 (5), 1115-1120 (2009).
[3] K. Fukuda, A. Moriyama and T. Iwata, Journal of Solid State Chemistry 178 (6), 2144-2151 (2005).