STUDY OF SR2-XPBXP2O7 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-2) SOLID-SOLUTIONS AND SINGLE-CRYSTAL STRUCTURE OF SR1.34PB0.66P2O7

Powder diffraction analysis of materials of the binary mixture Sr2P2O7 -Pb2P2O7 reveals the existence of two solid solutions: A, 0.2 less-tha n-or-equal-to x less-than-or-equal-to 1.25, isotypical to alpha-Ca2PO7 but similar to alpha-Sr2P2O7; B, 1.5 less-than-or-equal-to x less-tha n-or-equal-to 2, isotypical to Pb2P2O7. The structure of Sr1.34Pb0.66P 2O7 determined by single-crystal X-ray analysis is isotypical to alpha -Ca2P2O7; monoclinic P2(1)/n, a = 5.433(4) angstrom, b = 8.944(6) angs trom, c = 13.183(6) angstrom, beta = 90.12(5)degrees, V = 640.6(7) ang strom3, D(x) = 4.438 g cm-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu( Mo Kalpha) = 287.64 cm-1, R = 8.6% for 1018 observed reflections. Sr a nd Pb exist on two mixed sites of varying occupancies, both nine coord inated: site 1, M-0 average distance 2.69(2) angstrom; site 2, M-O ave rage distance 2.72(2) angstrom.