Synthesis and structure of phosphates M3R4(PO4)(6) (M = Cu, Co; R = Fe, Cr, Ga, In) and their interaction with hydrogen

The formation of phosphates M3R4(PO4)(6)(M2+ = Cu, Co; R3+ = Fe, Cr, Ga, In ) are studied. For M = Cu or Co and R = Fe or Cr, the resulting phases are isostructural with Fe-7(PO4)(6). The structures of M3R4(PO4)(6) (M2+ = Cu, Co; R3+ = Fe, Cr) are studied by the Rietveld method (space group P (1) ove r bar, Z = 1). The crystallographic data are for Cu3Fe4(PO4)(6): a = 7.9298 (1) Angstrom, b = 9.3279(2) Angstrom, c = 6.2557(1) Angstrom, alpha = 107.1 60(1)degrees, beta = 101.011(1)degrees, gamma = 105.831(1)degrees, V = 406. 38 Angstrom (3); for Cu3Cr4(PO4)(6): a = 7.8313(2) Angstrom, b = 9.2645(2) Angstrom, c = 6.2185(1) Angstrom, alpha = 107.202(2)degrees, beta = 100.916 (2)degrees, gamma = 106.408(2)degrees, V = 394.68 Angstrom (3); for Co3Fe4( PO4)(6): a = 7.9096(1) Angstrom, b = 9.2885(2) Angstrom, c = 6.3419(1) Angs trom, alpha = 108.487(2)degrees, beta = 101.518(2)degrees, gamma = 104.666( 2)degrees, V = 407.10 Angstrom (3); for Co3Cr4(PO4)(6): a = 7.8561(3) Angst rom, b = 9.2350(5) Angstrom, c = 6.2785(3) Angstrom, alpha = 108.173(3)degr ees, beta = 101.808(2)degrees, gamma = 105.329(2)degrees, V = 396.38 Angstr om (3). The compositions of the M3R4(PO4)(6) phases (M = Cu, Co; R = Fe, Cr ) differ from the stoichiometric ones. The iron-containing compounds form t he M3-deltaFe4+delta(PO4)(6) phases. The reasons behind the deviation from stoichiometry are discussed. The interaction of phosphates M3Fe4(PO4)(6) (M = Cu, Co, Ni) With hydrogen at temperatures 300-800 degreesC is studied.