Electronic structure of ordered and disorderedCu3Au: The behavior of the Au 5dbands

The electronic behavior of the Au 5d bands in the ordered and disordered ${\mathrm{Cu}}_3$Au has been investigated with x-ray-absorption near-edge structure (XANES) and Al Kα x-ray (1486.6 eV) photoemission (XPS) measurements. The XANES and XPS results clearly show that Au loses 5d character (count) upon the formation of ${\mathrm{Cu}}_3$Au in both ordered and disordered phases and that the Au 5d count depletes more in the ordered phase than in the disordered phase. In addition, the Au 5d hole population is found to be nonstatistical ([${\mathit{h}}_{5/2}$]:[${\mathit{h}}_{3/2}$]<1:1) in ${\mathrm{Cu}}_3$Au alloys as compared to a near-statistical 5d population ([${\mathit{h}}_{5/2}$]:[${\mathit{h}}_{3/2}$]∼2:1) in ${\mathrm{AuAl}}_2$ and ${\mathrm{AuGa}}_2$ (Au–non-transition-metal compounds). These observations are interpreted on the basis of the charge-compensation model. The nonstatistical Au 5d hole distribution derived from XANES together with the photoemission results indicates uneven Au 5${\mathit{d}}_{5/2}$ and 5${\mathit{d}}_{3/2}$ contribution (relativistic effect) in the Au 5d–Cu3d interaction in ${\mathrm{Cu}}_3$Au.