NMR RELAXATION IN GLASSY CU-AS-SE AND CU-AS-S

Nuclear magnetic resonance (NMR) of Cu-63 and nuclear quadrupole resonance (NQR) of As-75 ave been used to study relaxation effects and the possibility of local atomic diffusion in the Cu-As-S and Cu-As-Se glassy systems. The frequency and temperature dependences of the spin-lattice and spin-spin relaxation times have been measured. The NMR spin-lattice relaxation measurements for Cu-63 in the Cu-As-Se and Cu-As-S glassy systems suggest that the spin-lattice relaxation rate T1(-1) is probably dominated by two relaxation mechanisms depending on the temperature. For T < 300 K, T1(-1) for Cu-63 and As-75 exhibits a weak temperature dependence, which has been frequently observed for As-75 in the chalcogenide glasses and many other nuclei in the oxide glasses. For T > 300 K, on the other hand, a much more efficient relaxation mechanism takes over where both T1(-1) and T2(-1) increase rapidly with temperature. We suggest that this sudden decrease in the relaxation times is probably due to the local diffusion of Cu. The dramatic decrease of T2 with temperature for T > 300 K is anomalous and may be related to clustering of copper atoms in these glasses.