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

Four new ternary compounds Zr₅M_1-xPn_2+x (M=Cr, Mn; Pn=Sb, Bi) were synthesized by arc-melting and annealing at 800 °C. They crystallize in the tetragonal W₅Si₃-type structure. The crystal structure of Zr₅Cr_0.49(2)Sb_2.51(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) Å, c=5.5600(3) Å). Four-probe electrical resistivity measurements on sintered polycrystalline samples indicated metallic behavior. Magnetic susceptibility measurements between 2 and 300 K revealed temperature-independent Pauli paramagnetism for Zr₅Cr_1-xSb_2+x and Zr₅Cr_1-xBi_2+x, but a strong temperature dependence for Zr₅Mn_1-xSb_2+x and Zr₅Mn_1-xBi_2+x which was fit to the Curie-Weiss law for the latter with θ=-11.3 K and μ_eff=1.81(1) μ_B. Band structure calculations for Zr₅Cr_0.5Sb_2.5 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.