Showing papers by "Debnarayan Jana published in 2005"

Defect dynamics in annealed ZnO by positron annihilation spectroscopy

Abstract: As-supplied polycrystalline ZnO samples (purity 99.9% from Sigma-Aldrich, Germany) have been annealed at different temperatures and subsequently characterized by positron annihilation spectroscopy, x-ray-diffraction (XRD) analysis, thermogravimetric analysis (TGA), and resistivity measurements. Positron annihilation lifetime analysis and coincidence Doppler-broadened electron-positron annihilation γ-radiation (CDBEPAR) line-shape measurements have been employed at a time to identify the nature of defects in differently annealed ZnO materials. Annealing up to 300°C, an increase of defect lifetime (τ2) as well as shape parameter (S parameter) has been observed. Further annealing causes a large decrease of τ2 and S parameter. TGA study shows considerable mass loss from ZnO as the annealing temperature is increased above 300°C. This is possibly due to oxygen evaporation from the sample. The c-axis lattice parameter, extracted from the XRD spectra, shows an increase due to annealing above 600°C, which is a sig...