ASM 2019

Talk (C3)


Stability of non-metal dopants to tune the photo activity of TiO2 anatase: A hybrid DFT study

 

Pooja Basera* and Saswata Bhattacharya

Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016

*pooja.basera[at]physics.iitd.ac.in

 

Abstract

Titanium dioxide (TiO2) anatase, as an important semiconductor metal oxide, has been widely investigated in the field of photocatalytic devices. However, the major drawback is its large bandgap of 3.2 eV, which restricts its applications in the visible region range. We report here using state-of-the-art hybrid density functional and ab initio atomistic thermodynamics the stability and meta-stability of different non-metal dopants X (X= N, C, S, Se) as a function of charge state at realistic temperature and pressure. We have addressed several non-metals dopants (X) in TiO2 at plausible positions viz. X substituted O, X as interstitial and configuration in which substitution and interstitial both present simultaneously. We have obtained from defect formation energies at experimental relevant condition, that Se interstitial defect in the p-type region (with two hole trapped) is energetically most favored to provide visible region photo-absorption in TiO2 whereas N substitution (with one electron trapped) is the most abandoned defect in the n-type region. We have concluded that the most stable states in X doped TiO2 are not the neutral defects but the charged defects. The individual effect of bond-making/breaking and charge carrier trapping energies further validates these findings. In addition, we have adopted one particle Green's function (GW) method and higher order Green's function equation i.e Bethe-Salpeter Equation (BSE) in order to obtain a high-quality description of electronic and optical properties of pristine and doped TiO2. We have obtained that optical properties of doped TiO2 are highly anisotropic. The most evident hallmark of the doped system is the appearance of absorption peaks at low energy below 3 eV, to give rise visible-light absorption, which is in agreement with experimental observations.


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