hide
Free keywords:
intermetallic phases; gamma-brass type; zinc; platinum; crystal structure
Abstract:
The gamma-brass type phase Pt2Zn11-delta (0.2 < 6 < 0.3) was prepared by reaction of the elements in evacuated silica ampoules. The structures of crystals grown in the presence of excess zinc or alternatively excess platinum were determined from single crystal X-ray diffraction intensities and confirmed by Rietveld profile fits. Pt2Zn10.72(1) crystallizes in the space group 1 (4) over bar 3m, a = 908.55(4) pm, Z = 4. The structure refinement converged at R-F = 0.0302 for I-o > 2sigma (I-o) for 293 symmetrically independent intensities and 19 variables. The structure consists of a 26 atom cluster which is comprised of four crystal lographically distinct atoms. The atoms Zn(1), Pt(1), Zn(2) and Zn(3) form an inner tetrahedron IT, an outer tetrahedron OT, an octahedron OH, and a distorted cuboctahedron CO respectively. About 14% of the Zn(1) sites are unoccupied. Pt2Zn10.73 melts at 1136(2) K. It is a moderate metallic conductor (rho(298) = 0.2-0.9 mOmega cm) whose magnetic properties (chi(mol) = -4.6 10(-10) to -5.4 10(-10) m(3) mol(-1)) are dominated by the core diamagnetism of its components.
