Free-Volume Nanostructurization in Ga-Modified As(2)Se(3) Glass

Different stages of intrinsic nanostructurization related to evolution of free-volume voids, including phase separation, crystalline nuclei precipitation, and growth, were studied in glassy As(2)Se(3) doped with Ga up to 5 at. %, using complementary techniques of positron annihilation lifetime spectroscopy, X-ray powder diffraction, and scanning electron microscopy with energy-dispersive X-ray analysis. Positron lifetime spectra reconstructed in terms of a two-state trapping model testified in favor of a native void structure of g-As(2)Se(3) modified by Ga additions. Under small Ga content (below 3 at. %), the positron trapping in glassy alloys was dominated by voids associated with bond-free solid angles of bridging As(2)Se(4/2) units. This void agglomeration trend was changed on fragmentation with further Ga doping due to crystalline Ga(2)Se(3) nuclei precipitation and growth, these changes being activated by employing free volume from just attached As-rich glassy matrix with higher content of As(2)Se(4/2) clusters. Respectively, the positron trapping on free-volume voids related to pyramidal AsSe(3/2) units (like in parent As(2)Se(3) glass) was in obvious preference in such glassy crystalline alloys.