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Abstract

By reacting platinum with alkali metals (A = K, Rb, Cs) a new family of
binary alkali metal platinides has been synthesized and characterized
by chemical analysis, X-ray powder diffraction, thermal analysis (DTA
and DSC), and magnetic measurements. All three compounds exhibit
similar XRD-patterns with strong reflections that can be indexed on the
basis of a rhombohedral crystal system (KxPt: a = 2.6462(1), c =
17.123(1); RbxPt: a = 2.6415(1) angstrom, c = 17.871(1)angstrom; CsxPt:
a = 2.6505(1) angstrom, c = 18.536(1) angstrom; x < 1/2). The a lattice
constant is independent on the alkali metal used and of value close to
the Pt-Pt distance in NaPt2 (2.645 angstrom). The c parameter increases
monotonically with the growing atomic radius of the alkali metal. The
average structure of the alloys consists of cubic close packed layers
of platinum atoms with layers of disordered alkali metals in between.
For all compounds besides the strong reflections small satellites are
observed which cannot be indexed together with the rhombohedral peaks
in any rational 3-dimensional lattice. However, these satellites can be
indexed as incommensurate modulations within the ab plane (found
propagation vectors k = (0.1011, 0.2506, 0) for CsxPt, and k = (0.0168,
0.2785, 0) for RbxPt).