Nasima Khatun

Role of oxygen vacancies and interstitials on structural phase transition, grain growth, and optical properties of Ga doped TiO2

A systematic study on the effect of gallium (Ga) doping (0u2009≤u2009xu2009≤u20090.10) on the structural phase transition and grain growth of TiO2 is reported here. X-ray diffraction spectroscopy and Raman spectroscopy confirm that Ga doping inhibits the phase transition. Activation energy increases from 125 kJ/mol (xu2009=u20090.00) to 300 kJ/mol (xu2009=u20090.10) upon Ga incorporation. X-ray photoelectron spectroscopy shows the presence of Ti3+/Ga3+ interstitials, substitution (Ti4+ by Ga3+), and oxygen vacancies in the samples. At lower doping (x ≤ 0.05), interstitials play a more significant role over substitution and oxygen vacancies, thereby resulting in a considerable lattice expansion. At higher doping (x ≥ 0.05), the effect of interstitials is compensated by both the effect of substitution and oxygen vacancies, thereby resulting in relatively lesser lattice expansion. Inhibition of the phase transition is the result of this lattice expansion. The crystallite size (anatase) and particle size (rutile) both are reduced due to Ga incorporation. It also modifies optical properties of pure TiO2 by increasing the bandgap (from 3.06 to 3.09u2009eV) and decreasing the Urbach energy (from 58.59 to 47.25u2009meV). This happens due to regularization of the lattice by the combined effect of substitution/interstitials and oxygen vacancies.A systematic study on the effect of gallium (Ga) doping (0u2009≤u2009xu2009≤u20090.10) on the structural phase transition and grain growth of TiO2 is reported here. X-ray diffraction spectroscopy and Raman spectroscopy confirm that Ga doping inhibits the phase transition. Activation energy increases from 125 kJ/mol (xu2009=u20090.00) to 300 kJ/mol (xu2009=u20090.10) upon Ga incorporation. X-ray photoelectron spectroscopy shows the presence of Ti3+/Ga3+ interstitials, substitution (Ti4+ by Ga3+), and oxygen vacancies in the samples. At lower doping (x ≤ 0.05), interstitials play a more significant role over substitution and oxygen vacancies, thereby resulting in a considerable lattice expansion. At higher doping (x ≥ 0.05), the effect of interstitials is compensated by both the effect of substitution and oxygen vacancies, thereby resulting in relatively lesser lattice expansion. Inhibition of the phase transition is the result of this lattice expansion. The crystallite size (anatase) and particle size (rutile) both are reduced due to Ga ...

Size and strain dependent anatase to rutile phase transition in TiO2 due to Si incorporation

Powders with compositions Ti(1−x)SixO2 (where 0u2009≤u2009xu2009≤u20090.25) were prepared to systematically study the effects of Si doping on anatase to rutile phase transformation. Samples were synthesized using a modified sol–gel route and were heat treated at various temperature in 450–950xa0°C range. XRD, Raman Spectroscopy, UV–vis spectroscopy, SEM, TEM were used to study the effects of dopant concentration and heat-treatments on the crystal structure, crystallite size and particle size. Rutile phase was found to occur only above a critical crystallite size. Si doping was found to delay the onset of anatase to rutile phase transformation from 500xa0°C (for composition xu2009=u20090) to 800xa0°C (for xu2009=u20090.25) through the lattice strain and crystallize size modification. Interplay between the average crystallite sizes, lattice strain, annealing temperature, and their effect on phase transition are discussed in terms of Si incorporation in lattice.