Nuclear magnetic resonance studies on Cu3AU, CuAu and CuAu3 alloys

Nuclear magnetic resonance (NMR) measurements of Cu-63 nuclei have been carried out on Cu3Au, CuAu and CuAu3 alloys with different degrees of order. The spin-echo spectra obtained from the disordered and the ordered CuAu3 phases exhibit an intense sharp resonance line. On the other hand, the characteristic resonance line broadened owing to second-order quadrupole interaction appears in the spin-echo spectra from the fully ordered Cu3Au and CuAu I phases. The spectra from the partially ordered Cu3Au and CuAu I phases and the high-temperature CuAu II phase can be fitted by the superposition of the broad line for the ordered state and the sharp line for the disordered state. It is demonstrated that the order-disorder transition for these alloys occurs heterogeneously, in contrast with the result of X-ray diffraction analysis. The NMR parameters such as the Knight shift K and the quadrupole coupling constant e(2)qQ/h are evaluated far the ordered and disordered phases for three kinds of ahoy of different concentrations.