Thermal expansion of type A carbonate apatite

Type A carbonate apatite powder, in which carbonate ion was completely substituted for the hydroxyl site, was synthesized by heating a low crystalline and stoichiometric hydroxyapatite powder under flow of a dry carbon dioxide gas at 1000 °C for 24 h. Its chemical formula was determined to be Ca ₁₀(PO₄)₆(CO₃) _0.93±0.06 from compositional and infrared spectroscopic analyses. The X-ray and neutron diffraction patterns of type A carbonate apatite showed the extra diffractions attributed to monoclinic symmetry with the space group Pb. The thermal expansion property of the type A carbonate apatite was determined from neutron powder diffraction data at 25, 200, 400 and 500 °C. The extra diffractions attributed to the monoclinic symmetry were not diminished at the high temperatures. The thermal lattice expansion coefficients were, for the first time, calculated to be α_a = 13.1 × 10 ^-6 °C^-1, α_b = 34.9 × 10 ^-6 °C^-1 and α_c = 8.1 × 10 ^-6 °C^-1 by using a Le Bail refinement.