Heat capacity of Sr10(PO4)6Cl2 and Ca10(PO4)6Cl2 by DSC

Strontium and calcium chloroapatites were synthesized by wet chemical method, characterized by X-ray diffraction and are found to be phase pure materials. The measured room temperature lattice parameter of Ca10(PO4)6Cl2 is a = 9.523 Å, c = 6.855 Å and for Sr10(PO4)6Cl2 is a = 9.876 Å, c = 7.188 Å. Heat capacity measurements were carried out on Ca10(PO4)6Cl2 and Sr10(PO4)6Cl2 by DSC in the temperature range 298–800 K. The heat capacity values of Sr10(PO4)6Cl2 is higher at all temperatures than Ca10(PO4)6Cl2. Enthalpy and entropy increments were computed. Heat capacity values of Ca10(PO4)6Cl2 and Sr10(PO4)6Cl2 at 298 K are 758 and 868 J K−1 mol−1, respectively.