SrPt2Al2 – A (3+2)D-incommensurately modulated variant of the CaBe2Ge2 type structure

Abstract

Abstract The first ternary compound in the Sr–Pt–Al system, SrPt2Al2, was synthesized by melting of the elements in a sealed niobium tube in a high frequency furnace. The structure of SrPt2Al2 was determined by single-crystal X-ray diffraction on the basis of data sets recorded at 90, 150, 210, 270 and 300 K. The compound crystallizes in an incommensurately modulated (3+2)D structure being related to the tetragonal primitive CaBe2Ge2 type structure. The structure was refined in the orthorhombic superspace group Pmmn(α,0,0)0s0(0,β,0)s00 (α=0.222(1) a*, β=0.224(1) b*, a=b=436.89(5), c=1010.16(13) pm at 90 K) with R M=0.0403, R S,1=0.0597 and R S,2=0.2046. The structural relation with CaBe2Ge2 along with a refinement in the tetragonal superspace group P4/nmm(α,0,0)0000(0,α,0)00s0 is discussed with respect to the temperature dependence of the q-vectors and by group-subgroup relations. The modulation, from the standpoint of the crystal chemistry, is mainly caused by the distortion of the Pt arrangements within the pseudo-tetragonal ab plane.