POSSIBLE ATOMIC DIFFUSION OF CU IN GLASSY CU-AS-SE

Due to its impact on various metastable changes in the electrical conductivity, atomic diffusion in amorphous semiconductors has become a very important subject. In the glassy Ag-As-S system, previous measurements suggest that the increase in the ionic conductivity for T > 300 K is probably due to atomic diffusion of Ag. In this paper, the temperature and compositional dependences of the spin-lattice and spin-spin relaxation times T1 and T2, respectively, of Cu-63 NMR are used to investigate the possibility of Cu atomic diffusion in glassy Cu-As-Se. For T < 300 K, we report a weak temperature dependence of T1 similar to that which has been observed frequently for other chalcogenide and oxide glasses. For T > 300 K, however, we observe a sharp decline of T1 and T2. Also, the magnetization recovery curves appear to fit a stretched exponential M = Moexp[-(t/T1)alpha] with alpha = 1/2. We interpret these results as suggesting that the relaxation process at high temperatures is probably dominated by an inhomogeneous diffusion of copper atoms.