| Potassium tantalite niobate crystal?KTa1-x Nbx O3?is a solid solution of potassium niobate?KNbO3?and potassium tantalate?KTaO3?,which has excellent electro-optical properties.Its secondary electro-optical coefficient can reach 10-14V2/m2.It is considered to be an excellent electro-optical material for optical devices.KTN crystal is also a typical ferroelectric material,and tetragonal KTN crystal has obvious domain structure.Researchers believe that the excellent electro-optical properties of KTN crystal are related to its internal domain structure.Therefore,the study of domain structure of KTN crystal is of great significance for its device application.Meanwhile,doping KTN crystal with manganese and iron ions can enhance its photorefractive properties significantly which increases the possibility of its application in optical information storage.In this study,Mn and Fe doped KTN crystals?Mn:Fe:KTN crystals?were grown by the top seed Czochralski method.The physical properties of Mn:Fe:KTN crystals were studied which laid a foundation for further research.The dielectric temperature spectrum of Mn:Fe:KTN crystal was measured by bridge method,and the Curie temperature of the crystal was determined.The lattice constants of Mn:Fe:KTN crystals were obtained by X-ray diffraction?XRD?.The ferroelectric domains were observed by a polarizing microscope.The primary and secondary electro-optic coefficients of crystals were measured at variable temperature conditions.The results were used to calculate the space charge field.The coercive fields of KTN crystals at different temperature conditions were obtained by the polarization-electric filed hysteresis loops tests.A digital holographic system for non-destructive,in-situ and real-time observation was studied.The geometrical optics principle of digital holographic system was given theoretically,and the image processing was analyzed and programmed.The electro-optical coefficients of Mn:Fe:KTN crystals were measured by double beam diffraction method and digital holographic system.By comparing the test results,the overall evaluation of the digital holographic system was carried out.The pre-magnification method of digital holographic microscopy system was designed and experimented,and a pre-magnification method suitable for dynamic observation of domain structure was obtained.The magnification effect was 5 times and the images were clear.It was used as the pre-magnification scheme for domain observation experiment.The effect of external field on domain structure evolution of Mn:Fe:KTN crystal was studied.Field-induced domain structure evolution of Mn:Fe:KTN crystals was observed by the digital holographic microscopy system.Two-wave coupling method was used to write gratings above Curie temperature,and the quality of gratings was characterized by digital holographic system.The size of the internal space charge field was calculated by using the measured results,and the formation process of domain structure under different external field conditions was studied by combining the coercive field data.Based on the evolution of domain structure and the relationship between space charge field and coercive field,the mechanism of domain structure evolution induced by external field was analyzed. |
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