Structural, magnetic, and spectroscopic studies of YAgSn, TmAgSn, and LuAgSn

摘要

The rare earth-silver-stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P6(3)MC, Z = 2, a = 468.3(1), c = 737.2(2)pm, wR(2) = 0.0343, 353 F-2 values, 12 variables for YAgSn, and ZrNiAl type, P (6) over bar 2m, a = 726.4(2), c = 443.7(1) pm, wR(2) = 0.0399, 659 F-2 values, 15 variables for TmAgSn, and a = 723.8(2), c = 442.47(9) pm, wR(2) = 0.0674, 364 F-2 values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with lambda = 48.725 pm, in order to clarify the silver-tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag-Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag-Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie-Weiss paramagnet with an experimental magnetic moment of 7.2 mu(B)/Tm. No magnetic ordering is evident down to 2K. The local environments of the tin sites in these compounds were characterized by Sn-119 Mossbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mossbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental Sn-119 nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag-Sn bonds and also significant Ag-Ag bonding in LuAgSn. (c) 2006 Elsevier Inc. All rights reserved.