Hydrogenation Influences on the Structural, Optical, and Insulating Properties of (Bi+Cr) Codoped Anatase TiO2 Nanoparticles

Abstract

AbstractThis 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.