Synthesis and crystal structure of Ca9Cu1.5(PO4)(7) and reinvestigation ofCa9.5Cu(PO4)(7)

Ca9Cu1.5(PO4)(7) was synthesized by the solid-state method at 1273 K follow ed by quenching in air. Crystal structure of Ca9Cu1.5(PO4)(7) was refined b y the Rietveld method: space group R3c, a = 10.3379(1) Angstrom, c = 37.189 8(3) Angstrom, Z = 6 with R-wp = 4.87%, R-p = 3.67%, S = 1.58, R-I = 2.42%, R-F = 1.07%. The structure of Ca9Cu1.5(PO4)(7) is isotypic with beta -Ca-3 (PO4)(2) and Ca9.5Cu(PO4)(7). The M(5) site is fully occupied, and the M(4) site is half occupied by copper canons. The M(1)-M(3) sites are occupied b y calcium canons. Copper canons in the M(4) site are displaced from the thr eefold axis due to long distances M(4)-O. Reinvestigation of crystal struct ure of Ca9.5Cu(PO4)(7) showed that the M(5) site is occupied by 0.79(1)Cu2 + 0.21Ca(2+), and other copper canons locate in the M(4) site. (C) 2001 El sevier Science Ltd. All rights reserved.