Dimorphic YbPdSn with ZrNiAl and TiNiSi type structure

Abstract

Abstract Two modifications of YbPdSn were prepared from the elements in sealed tantalum tubes at 870 K (α-YbPdSn) and 1400 K (β-YbPdSn). Both structures were refined from single crystal X-ray data: α-YbPdSn (ZrNiAl type structure), space group P[unk]2m, a = 759.0(2) pm, c = 376.98(9) pm, wR2 = 0.0541, 344 F 2 values, 14 variables; β-YbPdSn (TiNiSi type structure), space group Pnma, a = 718.7(1) pm, b = 458.3(1) pm, c = 796.1(1) pm, wR2 = 0.0455, 391 F 2 values, 20 variables. Structural features of both modifications are palladium-centered trigonal prisms formed by the ytterbium and tin atoms. The structural similarities between α- and β-YbPdSn and the relationship with the aristotype AlB2 is discussed in the framework of a group-subgroup scheme. Magnetic susceptibility data show Curie-Weiss behaviour for α-YbPdSn with μ exp = 4.2(1) μ B and θ = −75(2) K, indicating trivalent ytterbium. The susceptibility of β-YbPdSn can be fitted to a modified Curie-Weiss law with μ exp = 1.6(1) μ B, θ = −5(1) K and χ 0 = 3.0 × 10−9 m3/mol, suggesting a tendency towards divalent ytterbium. Temperature dependent resistivity measurements indicate metallic behaviour with room temperature values of 50 ± 20 μΩ cm for α-YbPdSn and 1300 ± 100 μΩ cm for β-YbPdSn. 119Sn Möss-bauer spectroscopic data show only one signal at δ = 1.84(2) mm/s (α-YbPdSn) and δ = 1.96(4) mm/s (β-YbPdSn) subjected to quadrupole splitting of ΔEq = 0.73(4) mm/s and ΔEq = 0.97(5) mm/s, respectively.