New structure and insight on the phase transition within the Cu-Pd-Sn system with 25 at. % Sn

Abstract

The Cu-Pd-Sn material system has a (Cu, Pd)3Sn phase region that shows an interesting and unexplored martensitic phase transformation. Literature on this system is limited and the description of the phases present is incomplete and partly contradictory. With focus on a specific Cu-rich composition in this phase region (Cu33Pd42Sn25) and having employed a combination of differential scanning calorimetry, X-ray diffraction, optical microscopy and density functional theory (DFT) methods we analyze the phases involved and the phase transformation temperatures. The martensitic transformation was found to occur at approximately 378 K upon heating and at 328 K under cooling conditions. The crystal structure of the high temperature (HT) austenite phase was identified as face centered cubic with lattice constant a=6.2261(1) Å at 473 K. DFT simulations of plausible atomic arrangements indicated that the HT phase was an L21 (Fm3¯m) type structure. The martensitic LT phase was found to be orthorhombic with a D011 (Pnma) type structure with lattice parameters a = 8.9860(3) Å, b=5.9347(2) Å and c=4.5328(2) Å at 298 K.