Study On External Field Modulation Of Perovskite Or Perovskite-like Oxide

External fields?such as strain,light,electric field,magnetic field,etc.?could significant impact the physical property of perovskite and perovskite-like oxide,which plays important role in their applications.In this thesis,our work mainly contain two parts.On one hand,we investigated the novel structural,optical and electronic properties of oxide thin films induced by substrate strain.On the other hand,we investigated the photoelectric properties of ultraviolet photoelectric detector based on KTaO₃.The main results are listed as following:1.We report the discovery of a new line defect in WO₃ epitaxial thin films obtained via a strain engineering approach.This unique line defect observed by scanning transmission electron microscopy?STEM?can be regarded as an A-site deficient pseudo-perovskite cell,rotated by 45 degrees.And line defect only propagates along a-and b-axis,as its propagation is forbidden along the c-axis.As the tensile strain increases,the number of line defects increases remarkably.Moreover,we examined the spatial distribution of line defects in these films.Line defects distribute only near the interface,and expand with the increasing tensile strain.STEM and DFT+U calculation indicate that the generation of line defects is one way to release the strain induced by the lattice mismatch.By analyzing the distinct electronic and optical properties of these strain-engineered line defect phases,we show the emergence of an intriguing local hole channel along the line defects and the highly tunable band structures.Such defect effects induced by strain can lead to novel functionalities in artificial designed oxide heterostructures.2.We report a visible-blind ultraviolet photoconductive detector with interdigitated electrodes based on KTaO₃?KTO?single crystals.Both the steady spectral responses and the transient photovoltaic measurements clearly exhibit a cutoff wavelength at 344nm?³.6 eV?,in accordance with the bandgap of KTO.The KTO photodetectors show a low dark current¹.5?pA at 20?V,and a high UV-to-visible rejection ratio with three orders of magnitude at room temperature.The quantum efficiency is 37.49%under 20V bias,and the Detectivity D*of 3.85×10¹² cm?Hz^0.5/W,which is comparable to that of silicon photodetectors in the UV region.The rise time of photoelectric response is²60 ps,indicating an ultrafast photoelectric response characteristic.