The influence of Ni additions on the relative stability of η and η' Cu_6Sn_5

摘要

We investigate how 5 at. % Ni influences the relative stability of η and η' Cu_6Sn_5. Synchrotron x-ray diffraction shows that, while Cu_6Sn_5 exists as η' at 25 and 150 ℃ and transforms to η on heating to 200 ℃, Cu_(55)Ni_(0.5)Sn_5 is best fit to η throughout 25-200 ℃. Our first principles calculations predict that η' is stable at T=0 K in both Cu_6Sn_5 and Cu_(5.5)Ni_(0.5)Sn_5, but that the energy difference is substantially reduced from 1.21 to 0.90 eV per 22 atom cell by the Ni addition. This effect is attributed to Ni developing distinct bonding to both Cu and Sn in the η phase.