Structure, Sn-119 solid state NMR and Mossbauer spectroscopy of RECuSn (RE = Sc, Y, La, Lu)

Sebastian CP, Fehse C, Eckert H, Hoffmann RD, Pottgen R

Abstract

X-ray pure samples of the stannides RECuSn (RE = Sc, Y, La, Lu) were prepared by arc-melting of the elements and subsequent annealing. The four stannides were investigated by X-ray powder and single crystal diffraction: ZrBeSi type, P6(3)/mmc, a = 458.3(2), c = 817.3(3)pm, wR2 = 0.0746, 148 F-2 values, 8 variable parameters for LaCuSn, NdPtSb type, space group P6(3)mc, a = 451.3 (1), c = 727.4(2) pm, wR2.= 0.0462,134 F-2 values, 10 variable parameters for YCuSn, a = 446.4(2), e = 709.0(2) pm, wR2 = 0.0214, BASF 0.47(2),240 F-2 values, 12 variable parameters for LuCuSn and LiGaGe type, space group P6(3)mc, a = 438.8(l), c =683.0(2) pm, wR2 0.0328, 220 F-2 values, 11 variable parameters for ScCuSn. The structures of the four stannides consist of layers of ordered [Cu3Sn3] hexagons. While the layers are planar in LaCuSn, a puckering effect is observed in YCuSn and LuCuSn. In ScCuSn with the smallest rare earth metal the puckering is that pronounced that a tetrahedral network occurs. The intralayer Cu-Sn distances are similar in the four compounds (262-268 pm), but the Cu-Sn interlayer distances decrease from 409 pm (LaCuSn) via 303 pm (YCuSn) and 289 pm (LuCuSn) to 276 pm (ScCuSn). Thus, as a function of the size of the rare earth metal, one observes a continuous transition from a two- to a three-dimensional [CuSn] network. The noncubic local symmetry at the tin site is reflected by a small nuclear electric quadrupolar splitting in the Sn-119 Mossbauer spectra and a moderate chemical shift anisotropy in Sn-119 solid state NMR. An inspection of all the Sn-119 chemical shift anisotropies measured for RETSn compounds (T= Cu, Ag, Au) reveals an excellent correlation with the magnitude of the electric field gradient present at the tin site as calculated from crystal structural data by the WIEN2k program. (c) 2006 Elsevier Masson SAS. All rights reserved.