Structural defects characterization of silver-phosphate glass nanocomposites by positron annihilation and related experimental studies

Abstract

The structural defects and their role in the formation and properties of the metal oxide glass nanocomposite xAgI–(1-x) (0.65Ag2O–0.35P2O5) have been studied using several sensitive spectroscopic techniques. The nanocomposite samples have been prepared by conventional melt-quenching method and the formation of nanocrystallites over the amorphous glassy matrices has been verified from X-ray diffraction and transmission electron microscopy studies. The optical band gap energies were determined from Tauc's plots of UV–Vis absorption spectra taken from a spectrophotometer. Special emphasis on the defect characterization and defects-mediated stages of evolution is made possible through positron annihilation lifetime (PAL) and coincidence Doppler broadening spectroscopic (CDBS) measurements, which further helped in the investigation of the growth of defects, especially the Ag+ ion vacancies, within the nanocomposites. A defect-specific positron lifetime is identified to represent positron trapping in the interfacial gaps between nanocrystallites and the amorphous glass matrices besides the vacancies of Ag+ ions. The longest positron lifetime component occurs due to the formation of orthopositronium in free volume holes of small sizes and it increased as an effect of agglomeration of the free volume holes within the amorphous glassy matrices at increased incorporation of AgI. The CDB spectra revealed the changing proximities of the Ag+ ion vacancies to the surrounding oxygen ions. The positron annihilation characteristics were especially indicative of the importance of the choice of stoichiometry in the formation of the nanocomposite and its exhilarating properties.