High-temperature neutron powder diffraction study of the structural phase transition between α and α′ phases in tricalcium phosphate Ca3(PO4)2

The α–α′ phase transition of tricalcium phosphate (TCP) has been investigated using high-temperature neutron powder diffraction and the Rietveld method. This transition occurs between 1458 and 1508 °C. Hysteresis is not observed between heating and cooling within the observed temperature interval of 25 °C. Structural refinement of the α′-TCP was successfully performed by the trigonal structure with space group P3̄m. The temperature dependence of unit-cell parameters of the TCP was determined around the α–α′ phase transition point for the first time. At the α–α′ phase transition point, the unit-cell parameters a, c, γ angle, and unit-cell volume discontinuously changed, indicating that the transition is of first order.