Ionic diffusion and local hopping in copper chalcohalide glasses measured using 64Cu tracer and 129I-Mössbauer spectroscopy

Abstract

For the first time, 64Cu tracer measurements of ionic diffusion were performed for several copper-rich glass compositions in the CuIAs 2Se 3, CuISbI 3As 2Se 3, CuIPbI 2As 2Se 3, CuIPbI 2SbI 3As 2Se 3 and Cu 2SeAs 2Se 3 systems. In accordance with previous a.c. impedance results and Wagner d.c. polarization measurements, it was found that pure Cu + ion-conducting glasses (50CuI17PbI 233As 2Se 3 and 50CuI20PbI 210SbI 320As 2Se 3) exhibit the highest copper tracer diffusion coefficients, D Cu , and the lowest diffusion activation energies. The values of D Cu at room temperature are higher by 4.5–5.5 orders of magnitude than those in an As 2Se 3 glass. The Haven ratio, H R , is found to be 0.52–0.61 (ternary glass) and 0.93–1.00 (quaternary glass). Short-range diffusional displacements of the iodide ions induced by the hopping Cu + ions are also detected in the CuIPbI 2SbI 3As 2Se 3 glassy system using 129I-Mössbauer spectroscopy in the temperature range of 4.2 to 305 K. The activation energy of local hopping, E h ≈ 0.31 eV, is very similar to that of bulk ionic conductivity (0.37 eV) and copper diffusion (≈ 0.33 eV). In contrast to CuI-based vitreous alloys, 50Cu 2Se50As 2Se 3 glass exhibits D Cu that are two to five orders of magnitude lower, and the copper ion transport number, t Cu + , is between 10 −3 and 10 −4 in the temperature range 140–170 °C.