High temperature phase transitions in CA_3(PO_4)_2 measured by neutron diffraction

摘要

High Resolution Powder Neutron diffraction data were collected on samples of Ca_3(PO_4)_2 (TCP) at temperatures ranging from ambient to 1525 deg C. Data collected showed and almost linear expansion in unit cell dimensions for the beta -TCP sample, followed by inversion to alpha -TCP at approximately 1300 deg C and finally inversion at 1500 deg C to super alpha -TCP. Data collected on the super alpha -TCP phase showed high tetragonal symmetry with a structure isomorphous with K2SO4. The structure of super -TCP was refined using the Rietveld method in space group of P6_3/mmc with unit cell dimensions of a=5.3626A and c=7.7017A at 1525 deg C.