Synthesis and crystal structure of Ca9Cu1.5(PO4)7 and reinvestigation of Ca9.5Cu(PO4)7

Abstract Ca 9 Cu 1.5 (PO 4 ) 7 was synthesized by the solid-state method at 1273 K followed by quenching in air. Crystal structure of Ca 9 Cu 1.5 (PO 4 ) 7 was refined by the Rietveld method: space group R 3c, a = 10.3379(1) A, c = 37.1898(3) A, 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 Ca 9 Cu 1.5 (PO 4 ) 7 is isotypic with β-Ca 3 (PO 4 ) 2 and Ca 9.5 Cu(PO 4 ) 7 . The M (5) site is fully occupied, and the M (4) site is half occupied by copper cations. The M (1)- M (3) sites are occupied by calcium cations. Copper cations in the M (4) site are displaced from the threefold axis due to long distances M (4)—O. Reinvestigation of crystal structure of Ca 9.5 Cu(PO 4 ) 7 showed that the M (5) site is occupied by 0.79(1)Cu 2+ + 0.21Ca 2+ , and other copper cations locate in the M (4) site.