Nonlinear optical properties of undoped and doped with Zr and Nb KTiOPO4 crystals
The structure of the ferroelectric phase of undoped KTiOPO4 and its solid solutions with zirconium and niobium is studied from first principles within the density functional theory. The second-order nonlinear susceptibility tensor and the spontaneous polarization of these materials are obtained. It is shown that an improvement in nonlinear optical properties of KTiOPO4 upon doping it with Zr and Nb cannot be explained by a systematic change in the composition of crystals and is apparently associated with the occurrence of defects. Possible structures of such defects are discussed.
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