First-principles Investigations of Fe Impurities in KNbO$_{3}$

The perovskite based material KNbO$_{3}$ has been studied extensively for its photorefractive properties, where the electro-optic effect combined with photoconductivity changes the local refractive index of the material in response to the incident intensities. The presence of a transition metal impurity like Fe is required for efficient photorefractive performance of this material. To shed light on the physical mechanism of this behavior, we perform first-principles calculations within the density functional theory framework. In this talk, we present the geometric and electronic structures of KNbO$_{3}$:Fe super cells and compare two cases: one in which the Fe$^{3+}$ impurity on the Nb$^{5+}$ site is compensated by an O vacancy in the first coordination shell and one in which the O vacancy is in the second coordination shell. Connections of this work to recent experimental measurements are discussed.