Photochromism of UV-annealed Fe-doped SrTiO3

Abstract

High-temperature annealing coupled with above bandgap UV illumination is an emerging approach to manipulate defect chemistries and resultant properties of electroceramics. To explore defect-processing-property relationships in these materials, an advanced multiphysics and multiscale model has been developed, which involves (a) high-fidelity first principles simulations of defect energies, (b) grand canonical thermodynamics of defect equilibria, (c) UV-perturbed defect formation energies from Shockley–Read–Hall generation and recombination, and (d) finite-element analyses of electrostatic potential and defect redistribution. Using this model, bottom-up insights into defect mechanisms associated with the UV-induced brown photochromism of Fe-doped SrTiO3 at high temperatures are provided. It is found that UV illumination leads to dissociation of the FeTi-vO complex and reduction in the oxygen vacancy concentration through exchange with the gas reservoir. Changes to these defect populations cause reionization of the FeTi defect from −1 to 0 charge state to maintain charge neutrality. This collectively gives rise to an increased concentration of FeTi0, which is the source of brown chromism. In addition, this model reproduces the experimentally observed electrical resistance degradation of samples annealed in this manner due to the increasing hole concentration in the material with time. The present model itself offers a route to guide and facilitate future efforts in this field.