Fluorite‐Related Phases in the System Li‐Pt‐Sn: Synthesis and Structures of Li2PtSn, Li3Pt2Sn3, Li2.27Pt2Sn3.73 and Li2.43Pt2Sn3.57

Abstract

AbstractThe intermetallic compounds Li2PtSn, Li3Pt2Sn3, Li2.27Pt2Sn3.73 and Li2.43Pt2Sn3.57 were synthesised by reaction of the elements in sealed tantalum tubes. They were investigated by X‐ray diffraction on powders and single crystals: F$\bar 4$ 3m, a = 626.0(1) pm, wR2 = 0.0834, 70 F2 values, 7 variables for Li2PtSn; Ia$\bar 3$ , a = 1264.3(1) pm, wR2 = 0.0340, 416 F2 values, 23 variables for Li3Pt2Sn3; Ia$\bar 3$ , a = 1269.7(1) pm, wR2 = 0.1130, 521 F2 values, 24 variables for Li2.27(1)Pt2Sn3.73(1); Ia$\bar 3$ , a = 1266.6(1) pm, wR2 = 0.1094, 620 F2 values, 25 variables for Li2.43(1)Pt2Sn3.57(1). The latter refinement was based on a crystal twinned by merohedry. Li2PtSn crystallises with an ordered variant of the BiF3 type. The other stannides adopt a superstructure of the fluorite type where all three subcell axes are doubled. In Li3Pt2Sn3 the platinum atoms are located on the calcium sites while the tin and 1/3 of the lithium atoms are ordered on the fluorine site. The remaining lithium atoms fill octahedral voids of the fcc arrangement of platinum. The superstructure is discussed on the basis of a group‐subgroup scheme and experimental evidence is given for a solid solution Li3−xPt2Sn3+x. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)