Constitutional defect structure of CuAl 2

The equilibrium phase CuAl 2 contains a small excess of Al atoms at all temperatures. From accurate X‐ray and density measurements, it was found that the simplest defect structure model consistent with the experimental results is substitutional, Cu 1 − x Al 2 + x ( x = 0.005–0.022 at room temperature). Such a defect type appears to be very unfavourable energetically because of the short Cu‐Cu‐site bond length of CuAI 2 compared to other C 16 compounds, and would be in contrast to that of the other known C 16 compounds.