THE TERNARY-SYSTEM URANIUM MANGANESE PHOSPHORUS - U2MN12P7 WITH ZR2FE12P7-TYPE STRUCTURE AND ISOTYPIC PHOSPHIDES A2MN12P7 (A-EQUIVALENT-TO-SC, SM, GD-LU, TH) AND U2T12P7 (T-EQUIVALENT-TO-FE, CO, NI)

The phase equilibria in the ternary system U-Mn-P were investigated. Three ternary phases were observed: UMn4P2, UMn5P3 and U2Mn12P7 with ZrFe4Si2-, YCo5P3- and Zr2Fe12P7-type structures respectively. The crystal structure of U2Mn12P7 Was refined from single-crystal X-ray data: P6BAR, a = 938.3(2) pm, c = 364.8(l) pm, Z = 1, R = 0.41 for 524 structure factors and 22 variable parameters. The lattice constants of the isotypic compounds A2Mn12P7 (A = Sc, Sm, Gd-Lu, Th) and U2T12P7 (T = Fe, Co, Ni) are reported. Within the series A2T12P7 (A = Eu, Yb, U; T = Mn-Ni) the cell volumes indicate that the A elements have the highest valency in the manganese compounds and the lowest valency in the nickel compounds. The phosphides A2Mn12P7 (A = Gd, Ho, Er, Tm) are paramagnetic at room temperature and show Curie-Weiss behaviour.