الملخص الإنجليزي
Abstract:
This paper presents the investigation results for pure and (Bi/Cr) codoped TiO2 nanoparticles (NPs) synthesized by using a hydrothermal precipitation technique. The synthesized NPs are characterized by using X-ray diffraction (XRD) and optical spectroscopy. The XRD patterns show a single anatase phase of an average nano-crystallite size ≈6–9 nm. In addition, it was noticed that the hydrogenation of the NPs of the ceramic samples reduced the crystallite sizes due to the creation of O-vacancies and microstrain. The optical absorption spectra show redshift of the bandgap. Moreover, an absorption hump in the high- wavelength range of 630–800 nm is observed and attributed to the d-d transitions in Cr3+ ions. Then, it is studied hydrogenation's significant effect on the absorption spectrum for λ > 370 nm, which attributes to the creation of a high density of point defects and structural microstrain that enhances the redshift of bandgap. The permittivity at 1 kHz of the prepared (Bi/Cr):TiO2 ceramic is found to be of large value (≈670), which is enhanced up to ≈103 by the hydrogenation. It is concluded that the hydrogenation in the present investigation supports the effects of the Bi3+ ions on the dielectric properties rather than that of Cr3+ ions, which mostly substitute the Ti ions (TiCr) due to the similarity of Ti3+ and Cr3+ ions. Thus, the measured dielectric constant of the hydrogenated sample [(Bi/Cr):TiO2-H] is almost equal to that value of the host TiO2 doped with only Bi ions (Bi:TiO2). Moreover, it is concluded that the hydrogenation has a negligible effect on the effective polaron hopping energy, but increases the sample maximum barrier height (WM) by ≈55% causing an increase in the measured values of the permittivity.
