Rapid, accurate phase quantification of multiphase calcium phosphate materials using Rietveld refinement

Rietveld refinement has been employed to estimate the crystalline phase compositions of multiphase calcium phosphate mixtures containing calcium hydroxyapatite [Ca₅(PO₄)₃OH], and alpha and beta tricalcium phosphate [Ca₃(PO₄)₂]. Two methods were employed using fixed structural models for all three phases and refining the zero offset, scale factors, lattice parameters and one peak breadth parameter using either a constant background (method A) or a background with two refined parameters (method B). Analysis of a matrix of quantitative standards across a broad spectrum of phase compositions indicates that method A results in small systematic deviations of the Rietveld phase compositions (< 1 wt%) from the nominal values, but the systematic deviations are eliminated by refining the background (method B). The methods require approximately 10 min to complete, and are suitable for quality control of calcium phosphate production (and potentially other multiphase systems) when accuracy, precision and time are all significant considerations.