SYNTHESIS AND CRYSTAL-CHEMISTRY OF NACACD MG2(PO4)(3), NEW ALLUAUDITETYPE PHOSPHATE WITHOUT TRIVALENT CATION

A new compound with an alluaudite structure-type, NaCaCdMg2(PO4)(3), w ith a = 12,005(2), b = 12,675(3), c = 6,546(1)Angstrom, B = 114,55(1)d egrees, space C2/c, has been synthesized by solid-state reaction techn ique. Infrared and Raman spectra suggest a partially ordered cation di stribution, and the structural refinement by the Rietveld method shows that Mg occupies the M(2) sites, whereas Na, Ca, and Cd are randomly distributed over M(1), X(1) and X(2). The M(2) octahedron is more regu larly shaped than M(1); X(1) and X(2) resemble an irregular octahedron , and a distorted trigonal prism, respectively.