STRUCTURE AND PROPERTIES OF ZR2NI2IN AND ZR2NI2SN

Zr2Ni2In and Zr2Ni2Sn were prepared from the elements by a reaction in an are melting furnace and subsequent annealing at 1070 K. They cryst allize with the tetragonal Er2Au2Sn-type structure of space group P-4/ mnm, a ternary ordered version of the Zr3Al2-type. Both structures wer e refined from single-crystal X-ray data: a = 715.1(1) pm, c = 663.5(1 ) pm, V = 0.3393(1) nm(3), wR2 = 0.0442, 324 F-2 values, 18 variables for Zr2Ni2In and a = 703.2(1)pm, c = 680.1(1)pm, V = 0.3363(1) nm(3), wR2 = 0.0668, 240 F-2 values, 18 variables for Zr2Ni2Sn The structures may be described as an intergrowth of CsCl and AlB2 slabs, According to electronic structure calculations, the occurrence of the superstruc ture is a second order effect and most likely due to packing reasons ( size of the zirconium cation), Compact polycrystalline samples of Zr2N i2In and Zr2Ni2Sn are Pauli paramagnetic and metallic conductors. (C) 1997 Academic Press.