Abstract
The successful synthesis of the metal oxide nanocomposite xMoO3–(1-x)(0.5SeO2–0.5ZnO) for x = 0.0, 0.1, 0.2, …, 0.9 by mixing and melt-quenching of the stoichiometric ratios of the metal oxides is reported in this work. X-ray diffraction patterns and transmission electron microscopy images confirmed the formation of the nanocomposites and their evolution to the amorphous glassy phase and newer nanocrystallites as x increased from 0–0.3, 0.3–0.7 and 0.7–0.9 respectively. The findings from Brunauer–Emmett–Teller isotherms also supported these observations, as one observed a significant enhancement in the pore volume and total pore surface area when the nanocomposites evolved from x = 0.3 to 0.9. The optical bandgap energy was another physical quantity that showed a steady decrease with increase in x and is attributed to the generation of additional electronic defect levels towards the conduction band within the bandgap. An important step that was taken up in this study was to characterize the defects in the composites by positron annihilation studies. Positron lifetimes and intensities pointed out the presence of vacancy-type defects within the nanocomposites, porous defects within the glassy amorphous phase and interfacial defects between the latter and the newer nanocrystallites formed. Coincidence Doppler broadened spectra revealed the decrease of positron trapping in cationic vacancies as x increased, showing that the annihilations within vacancy type defects decreased and in interfacial defects and nanocrystallite surfaces increased, confirming the formation of the newer nanocrystallites and their uniform dispersion in the glassy amorphous matrices.
Published Version
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