A radial distribution function analysis of an amorphous calcium phosphate with calcium to phosphorus molar ratio of 1.42.

Abstract

A radial distribution function (RDF) analysis was performed on amorphous, freeze-dried calcium phosphate prepared under conditions of pH=7.3–8.0 with Ca/P molar ratio of 1.42. Diffracted intensities were obtained by using reflection geometry, copper radiation, and a receiving graphite monochromator. For purposes of analysis, the material was treated as a random binary alloy consisting of calcium and phosphate ions. Major peak positions were found to occur atr=2.55, 3.75 and 6.40 A and were substantiated by the application of an artificial temperature factor. The first major peak was attributed to a superposition of peaks corresponding to the Ca−O and O−O distances. There is also evidence of a peak at 2.9 A which suggests the existence of a phosphorus-oxygen network, i.e. condensed phosphates. Densities obtained by this analysis and direct measurement agreed and were substantially less than the accepted value for Ca3(PO4)2. The area under the peak in the RDF corresponding to the unresolved Ca−O and O−O distances yields a coordination number of about 3.