Preparation and crystal structures of some binary pnictides of scandium, zirconium, and hafnium: Sc5Bi3, ZrBi, alpha-HfSb, HfBi, HfBi2, and the compound Zr5Bi3X1-x, possibly stabilized by an impurity (X)

The title compounds were prepared by reaction of the elemental components. Of these Sc5Bi3 is a new compound. Its orthorhombic beta -Yb5Sb3 type cryst al structure was determined from single-crystal X-ray data: Pnma, a = 1124. 4(1) pm, b = 888.6(1) pm, c = 777.2(1) pm, R = 0.024 for 1140 structure fac tors and 44 variable parameters. For the other compounds we have establishe d the crystal structures. ZrBi has ZrSb type structure with a noticeable ho mogeneity range. This structure type was also found for the low temperature (alpha) form of HfSb and for HfBi. For alpha -HfSb this structure was refi ned from single-crystal X-ray data: Cmcm, a = 377.07(4) pm, b = 1034.7(1) p m, c = 1388.7(1) pm, R = 0.043 for 432 F values and 22 variables. HfBi2 has TiAs2 type structure: Pnnm, a = 1014.2(2) pm, b = 1563.9(3) pm, c = 396.7( 1) pm. The structure was refined from single-crystal data to a residual of R = 0.074 for 1038 F values and 40 variables. In addition, a zirconium bism uthide, possibly stabilized by light impurity elements X and crystallizing with the hexagonal MO5Si3C1-x type structure, was observed: Zr5Bi3X1-x, a = 873.51(6) pm, c = 599.08(5) pin. The positions of the heavy atoms of this structure were refined from X-ray powder film data. Various aspects of impu rity stabilization of intermetallics are discussed.