The Optimization Of The Growth Process And The Investigate Of The Nonlinear Optical Properties On KTa_1-xNb_xO₃ Thin Films

Ferroelectric material, as an important information functional material with the features of ferroelectricity, dielectricity, piezoelectricity, pyroelectricity, electricphoton and nonlinear optics, can be widely used in the field of high and new technologies such as microelectronics, optoelectronics, integrated optics and micro mechanics, and has received a wider and wider publicity. Potassium tantalate niobate (KTa_1-xNb_xO₃, KTN) with perovskite structure has a good ferroelectricity, dielectricity and pyroelectricity, especially near Curie temperature, KTN cristal has a very high electro-optical coefficient and nonlinear optical coefficient, which makes KTN have an important application prospects in the key devices such as optical switch, optical waveguide, optical modulator, optical deflector, mode-locked laser in the technologies of optoelectronics, integrated optics and laser. KTN is also an earlier found material with photorefractive effect, having an important application value in optical recording, optical storage, optical information processing, and optical computing, etc.However, a large number of studies have shown that, in KTN the growing of big and high optical uniform cristal is very difficult, the powder is easily get agglomerated, the stoichiometric ratio of metal atom is easily deviated and there is Pyrochlore Phase in the ceramics and thin films because of high temperature in the crystallization process.Aiming at the problems which influence the performance of KTN and restrict the application of KTN material, this thesis for first time brings forward and adopts a new technique route and techniques method of making KTN nano-powder with hydrothermal method combining with solvothermal synthesis method, studies systematically under the hydrothermal reaction condition, the relation between reaction temperature, solvent type and PH value, the relation between reaction time and powder form, and the relation between particle size and material nature, successfully makes nano-powder with good dispersibility and high activiy. Based on the powder production, we adopt the atmosphere sintering ceramics method to make good KTN target material in low temperature which can meet the stoichiometric ratio. In order to probe the process integration and compatibility of KTN material with microelectronics and optoelectronic devices, based on systematic PLD Dynamics Theory and experiment researches having been made by our task force for years, we further optimise the technological condition of making KTN thin films with PLD technology, make experiments of producing high-oriented and epitaxy KTN thin films on different substrates. We have studied the characters of the thin films such as chemical composition of the surface, valence state and the vibration of chemical bond, using microstructure characterization measures such as XRD and AFM and mothods such as XPS, IR-Fourier Transform Spectrometry and Raman spectroscopy. In order to probe the application of low-dimensional KTN material on the device of planar lightguide, we have studied systematically the optical properties of KTN thin films by measuring the transmitted spectrum of KTN thin films and adopting calculation method of enveloping line proposed by Swanepoel, and got the optical parameters such as linear absorption coefficient and linear refractive index. We have studied the third-order nonlinear optical properties of thin films by adopting Z-scanning technology, got nonlinear absorption and nonlinear refractive index, and obtained the real part Rex⁽³⁾ and imaginary part Imx⁽³⁾ of third-order nonlinear polarization coefficient through theoretical calculation. The research based on this method on the third-order nonlinear optical properties hasn' t been reported publicly before at home and abroad. At last, by adopting first-principle calculation method, we have built a super primitive cell of KTN, and calculated the band-gap energy and electronic band structures of KTN thin films and got the theoretical results on dielectric function, refractive index and absorption coefficient.This thesis has the following characteristcs and innovations:(1) For the first time we have successfully made KTN powder of nanoscale which can meet the stoichiometric ratio by adopting hydrothermal and solvothermal methods, and provided a new design route for the production, application in devices and practical use of KTN ceramics and thin films. We have also made theoretical studies on the mechanism of hydro-thermal method and solvothermal synthesis method and the thermodynamic model of hydrothermal synthesis.(2) We have made KTa_0.65Nb_0.35O₃ thin films on the substrate of SrTiO₃ (100) by adopting PLD thin films making method. We've studied the influence of different substrates and deposition temperature on the surface pattern and crystallinity. The test of characterization and analysis has shown that, under optimised process condition, the thin films sample has a good crystallinity, the growth of thin films has a preferred orientation following (100) and the surface of thin films is smooth and uniform, and the arrangement of grains is dense.(3) We have studied the linear optical properties of KTN thin films by using the transmitted spectrum of KTN thin films, and got the relation between the refractive index and linear absorption coefficient of the thin films sample and the variation of wavelength. The measured refractive index is 2.32 whereλ= 790nm, which is close to the value of KTN crystal of the same component; concerning the Open and Closed-aperture Z-scan Curves, we have studied the linear and nonlinear optical properties of KTN thin films and got the thin films' nonlinear refractive index by measurement, which isγ= -0.181cm²/GW, nonlinear absorption coefficient,β= 3.97×10² cm/GW, and thereal part of Third-order Nonlinear Optical Susceptibility, Rex⁽³⁾ and the imaginative partImx⁽³⁾ are 2.56×10^-9 esuå’Œ1.11×10^-8 esu respectively. The research result has shownthat KTN thin films material is a very good nonlinear optical meterial.(4) We have built super primitive cell of KTN by adopting the first-principle calculation method and for the first time made theoretical studies on band structure, density of states and optical properties of KTN thin films by applying PPW method based on Density Functional Theory. The calculation result has shown that the optical property of KTN membran is decided by BO₆ octahedron, which controls the transition from the lower order conduction band to the higher order valence band, and we have got a theoretical results comparable to the the experiment.