Rietveld structure refinement of synthetic magnesium substituted beta-tricalcium phosphate

Rietveld method has been applied to refine the structure of magnesium substituted beta-tricalcium phosphate at a magnesium content of about 14 mol%. The results of the refinements, which show a final agreement factor R(wp) = 0.12, are in agreement with an almost complete substitution in two of the five crystallographically independent cation sites. The preference of magnesium for these two sites can be explained on the basis of the coordination geometry of the five different cation sites. Furthermore the results allow to interpret the discontinuity found around 10 magnesium mol% in the variation of the c axis as a function of magnesium content.