The system LaPO_4-Ca_3(PO_4)_2

摘要

A previously unknown phase diagram of the LaPO_4-Ca_3(PO_4)_2 system has been determined as a result of thermal, X-ray and microscopic investigations. The system contains a double orthophosphate Ca_3La(PO_4)_3 which exists above the 1230 deg C, transforms at 1270 deg C and melts congruently at 1890 +- 20 deg C. The high temperature modification of Ca_3La(PO_4)_3 is cubic: a = 9.937 A, z = 4, space group 143d. A limited solid solution having the formula Ca_(3-x)La_(2x/3)(PO_4)_2 (0 <= x <= 3/7) and a rombohedral beta-Ca_3(PO_4)_2 structure has been discovered in the system.