Structure and physical properties of ternary W5Si3-type antimonides and bismuthides Zr5M1-xPn2+x (M=Cr, Mn; Pn=Sb, Bi)

Four new ternary compounds Zr5M1-xPn2+x (M=Cr, Mn; Pn=Sb, Bi) were synthesized by arc-melting and annealing at 800oC. They crystallize in the tetragonal W5Si3-type structure. The crystal structure of Zr5Cr0.49(2)Sb2.51(2) was refined from powder X-ray diffraction data by the Rietveld method (Pearson symbol tI32, tetragonal, space group I4/mcm, Z=4, a=11.1027(6)A, c=5.5600(3)A). Four-probe electrical resistivity measurements on sintered polycrystalline samples indicated metallic behavior. Magnetic susceptibility measurements between 2 and 300K revealed temperature-independent Pauli paramagnetism for Zr5Cr1-xSb2+x and Zr5Cr1-xBi2+x, but a strong temperature dependence for Zr5Mn1-xSb2+x and Zr5Mn1-xBi2+x which was fit to the Curie-Weiss law for the latter with θ=-11.3K and μeff=1.81(1) μB. Band structure calculations for Zr5Cr0.5Sb2.5 support a structural model in which Cr and Sb atoms alternate within the chain of interstitial sites formed at the centers of square antiprismatic Zr8 clusters