Pt 2 AuCuNiSn, a High Entropy Alloy with a Large Atomic Size Mismatch

A new high entropy alloy, Pt2AuCuNiSn, has been obtained at comparatively low temperatures by a solid state reaction. A Rietveld refinement gave a satisfactory description of X-ray diffraction data obtained at ambient temperature. SEM/EDXmeasurements gave no indication for chemical inhomogeneities on a micron length scale. Temperature dependent in situ diffraction measurements using hard (lambda = 0.1204 A) radiation up to 875 K show several transient phases upon heating a mixture of the elements, consistent with results of DSC measurements. The parameter describing the variability of the radii of the constituent atoms, d_r, is uncommonly large (d_r = 8.7 %) and may be the origin of the instability of this alloy at high temperatures.