A MAGIC ANGLE SPINNING NMR-STUDY OF THE PHASE-DIAGRAM CA3-XZNX(PO4)2

The phase diagram Ca3-xZnx(PO4)2 has been investigated by 31P magic angle spinning NMR (MASNMR). The study demonstrates how MASNMR can be used to make clear distinction between regions of solid solution, line phases, and biphasic mixtures. The 31P MASNMR spectrum of the complex phosphate, β-Ca3(PO4)2, has been rationalized in terms of the known structure, and the broadness of the observed resonances has been attributed to the disorder caused by partial occupancy of one metal site. Variations in intensity and linewidth of the 31P MASNMR resonances, as zinc is substituted for calcium in the β-Ca3(PO4)2 framework to form a solid solution, have been interpreted by analogy with the isomorphous solid solution Ca3-xMgx(PO4)2. The intermediate phase α-CaZn2(PO4)2 has been identified as having no solubility in either end member and is characterized by two distinct isotropic resonances at 10.0 and 2.2 ppm. The spectra of a high-temperature form of each Ca3(PO4)2, CaZn2(PO4)2, and Zn3(PO4)2 have also been observed.