【作者】 李杨；

【导师】 周忠祥； Amar S.Bhalla；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2013， 博士

【摘要】 钽铌酸钾晶体KTa_1-xNb_xO₃（KTN）作为一种优异的非线性电光材料以及电控全息材料被广泛地研究和应用。目前KTN系材料的研究重点主要集中于富钽的组分，这些单晶组分的居里温度较低或在室温附近，通常具有很高的二次电光系数，但作为器件在工作的时候所产生的热量极容易造成其性能的不稳定，因此对工作环境要求极高。而富铌（x≥0.5）的KTN晶体可以通过调节钽铌比得到较高的居里温度，在室温下展现出良好的线性电光性能，与此同时，此类材料还表现出了十分优异的压电性能，是极具研究和应用价值的多功能材料。但由于室温铁电材料生长困难，其性能很少被报道。本工作采用改进的提拉法成功获得了尺寸约为1×1×2cm3高质量、少量掺杂锂元素的富铌K_0.95Li_0.05Ta_1-xNb_xO₃（x=0.52、0.60、0.69和0.78，KLTN）四种组分的单晶材料。继而对室温铁电的KLTN系单晶基本的光学性能、结构相变、热膨胀特性以及线性电光性能进行研究。同时，作为新型压电-电光多功能材料，KLTN系单晶压电谐振对其高频电光性能的增强效应也被测定以及讨论。室温铁电的KLTN单晶经过切割、抛光以及极化处理后，在可见光区域，可以实现极好的光学透过率。KLTN单晶的紫外吸收边和禁带宽度通过测试其透射谱而得知。利用最小偏向角法，精确地测量四个组分KLTN单晶的折射率。通过最小二乘法拟合，得到KLTN系单晶折射率色散的塞尔迈耶尔方程，研究对比不同组分KLTN单晶塞尔迈耶尔光学系数。对KLTN四个组分的晶体样品介电常数的温度和频率特性进行研究，确定不同组分的居里温度，分析组分对居里温度的影响以及介电性能的频率依赖关系。采用线性电压差动法，对KLTN系单晶的热膨胀形变以及系数进行研究。通过热膨胀测试的结果，分析材料结构相变机制与温度、组分以及晶体取向之间的关系。对比介电与热膨胀数据的差异，分析组分波动引起的峰值位置偏差。对比热释电与热膨胀数据的积分结果，讨论KLTN系晶体的自发极化与动态局域极化机制之间的关系。对富铌的室温铁电KLTN系单晶的线性电光性能进行细致地表征和分析，测得四个组分单晶的电光系数矩阵中所有的非零张量元γ₃₃、γ₁₃、γ₅₁以及有效电光系数γ_c，发现富铌KLTN系单晶具有很大的切向线性电光系数γ₅₁，并分析单晶电光性能的频率依赖特性。根据坐标系旋转的理论，结合实验所得的电光系数矩阵，模拟四方相KLTN晶体有效电光系数的三维空间分布，得到沿任意方向电光系数的大小。根据仿真的结果，由于电光矩阵中γ₅₁值很大，其对有效电光系数的贡献较大，致使电光系数在三维空间分布中的最大方向发生偏转，而不再沿原来的[001]方向。在高频调制电场下，讨论富铌KLTN系单晶的压电谐振对其电光性能的增强作用。研究结果表明谐振峰附近的电光响应会急剧的增加，峰值处的线性电光响应大小可以与低频电光响应相当，这为KLTN晶体的应用提供了更广阔的空间。本工作对富铌KLTN系晶体线性电光性能及其他相关性能进行大量的研究，结果预示着KLTN系材料有着巨大的潜力成为光电-压电-机电性能耦合的高质量多功能材料。更多还原

【Abstract】 As a good nonlinear electrooptic and electrical controlled holographic material,potassium tantinate niobate KTa_1-xNb_xO₃（KTN） was investigated and appliedbroadly. Current research work about KTN family is focusing on Ta-richcomposition, which has low Curie temperature near room temperature. Ta-rich KTNcrystal has large Kerr coefficient however the heat created by materials will induceinstability when the material was used in device. But for Nb-rich KTN system,through modifying the Ta-Nb ratio, we can obtain high Curie temperature and goodlinear electrooptic property at room temperature. At the meantime, KTN seriesmaterials also show excellent piezoelectric properties, thus KTN series crystal isone kind of multifunctional material deserve to be studied. But owing to thedifficulty of ferroelectrics single crystal growth, the report about Nb-rich KTNseries single crystal is scare.With a slight Li doped, high quality K_0.95Li_0.05Ta_1-xNb_xO₃（x=0.52,0.60,0.69and0.78, KLTN） single crystals were grown using Top Seeded Melt Growth method.The optical, dielectric phase transition, thermal expansion and linear electroopticproperties of KLTN single crystals were investigated. As piezoelectric-electroopticmultifunctional material, the piezo-resonance enhanced the electrooptic effect ofNb-riched KLTN single crystal was reported at the first time.For room temperature ferroelectric KLTN single crystal, good opticaltransmittance can be obtained after cutting, polishing and poling processing. Theultraviolet absorbing edge and band gap of KLTN single crystals were determinedby transmittance spectrum. The refractive indices of four compositions of KLTNsingle crystals were measured accurately by using the minimum deviation method.The Sellmeier’s dispersion equations of refractive indices and the Sellmeier opticalcoefficients for KLTN single crystals were obtained in terms of least squares fit.The temperature and frequency dependent dielectric properties of KLTN singlecrystals were investigated. The compositions and frequency dependent Curietemperature of Nb-riched KLTN singe crystal were determined.The thermal expansion strain and coefficient of KLTN single crystal werestudied by using LVDT method. Accoding to the thermal expansion results, analysethe relationship between structure phase transition and temperature, compositions,orientation. Comparing the results of dielectric and thermal expansion, discuss thedata peak disagreement by using the composition inhomogeneity. Comparing theresults of paryelectric and thermal expansion, the sponteous and dynamic local polarization mechanism of KLTN single crystals were studied.The low frequency dependent linear electro-optic （EO） properties of KLTNseries single crystals were studied at room temperature. The EO coefficients γ₃3, γ₁3,γ₅₁and effective EO coefficients of KLTN single crystals at the wavelength of0.633nm were measured. The large value of γ₅₁for KLTN series single crystals wasreported at the first time. The orientation dependent corresponding electroopticcoefficient of KLTN single crystal was calculated and simulated based on axesrotation theory and experimental results. It is found that owing to the contribution ofγ₅₁, the maximum orientation of EO coefficient in3-dimension space is deviatingfrom the [001] direction. The piezo-resonance enhances the EO properties for KLTNseries single crystals under high frequency modulation field were studied at the firsttime. The results indicated that the EO response sharply increase near resonancepeak where the EO coefficient is comparable with that at low frequency. Accordingto these results, KLTN series multifunctional material may obtain more broadlyapplication space.The linear EO properties and other related properties of KLTN series singlecrystals were investigated in this work. It is found that KLTN series single crystalhas large potential to optical-piezoelectric-mechanism coupling high qualitymultifunctional materials.更多还原