Synthesis and characterization of Pt(Cu₀.₆₇Sn₀.₃₃)

Abstract

Pt(Cu₀.₆₇Sn₀.₃₃) has recently been found in a natural sample. In order to characterize this new ternary compound, we synthesized it from the elements. Samples were characterized by X-ray powder diffraction, differential scanning calorimetry, thermal relaxation calorimetry, and scanning electron microscopy studies. Density functional theory (DFT)-based model calculations complemented the experimental studies. Pt(Cu₀.₆₇Sn₀.₃₃) was already formed at a relatively low temperature of 773 K. Rietveld refinement of Pt(Cu₀.₆₇Sn₀.₃₃) was carried out in the CuAu-type or L1₀-type structure, space group P4/mmm, with Pt on (0,0,0) and disordered Cu and Sn on (½, ½, ½), and Z = 1. The lattice parameters are a = 2.823(1) Å, c = 3.64(1) Å, and V = 29.00(4) ų, which are in good agreement with values obtained earlier for the natural sample and with the results of DFT calculations. The vibrational entropy for Pt(Cu₀.₆₇Sn₀.₃₃) is Sᵥᵢᵦ²⁹⁸.¹⁵ = 79.9(7) J mol⁻¹ K⁻¹. The pressure dependence up to 36(2) GPa of the unit-cell volume and the lattice parameters has been obtained by synchrotron-based powder diffraction using a diamond anvil cell. A fit of a third-order Birch–Murnaghan equation of state to the Pt(Cu₀.₆₇Sn₀.₃₃) (p, V) data results in a bulk modulus of B₀ = 215(27) GPa and B′ = 5(2).