Gaussian deconvolution of the antisymmetric stretch of the phosphate ion, ν3(P-O), overlapping at high end with the symmetric carbonate stretch, ν1(CO3), and at low end with the symmetric phosphate stretch, ν1(P-O) for HAp (a) and ACP (b) powders annealed at 5 °C/min up to 1000 °C. The ν3(P-O) band shape for the non-annealed ACP and ACP annealed at different heating rates: 5, 10, 20 and 50 °C/min (c). Crystallinity index (CI) of ACP and HAp precursors annealed at 1000 °C as a function of the heating rate, including the exponential fit enabling the prediction of CI from a known heating rate, x, in °C/min (d).