We investigate how 5 at. % Ni influences the relative stability of η and η′ Cu6 Sn5. Synchrotron x-ray diffraction shows that, while Cu6 Sn5 exists as η′ at 25 and 150 °C and transforms to η on heating to 200 °C, Cu5.5 Ni0.5 Sn5 is best fit to η throughout 25-200 °C. Our first principles calculations predict that η′ is stable at T=0 K in both Cu6 Sn5 and Cu5.5 Ni0.5 Sn5, 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.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)