【作者】 吴丰民；

【导师】 曹文武； 杨彬；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2013， 博士

【摘要】 弛豫铁电固溶体单晶因其具有十分优异的压电、机电等性能广泛地应用于传感器、超声马达及超声换能器等器件当中。最近几年，高质量、均匀的三元弛豫铁电单晶铌铟镁酸铅-钛酸铅[Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃，（PIN-PMN-PT）]备受研究领域的瞩目，在具有优异压电与机电等特性的同时，其高的居里温度、相变温度和大矫顽场等优良特性使之有很大潜力成为新一代的声功能材料。本论文以弛豫铁电单晶铌铟镁酸铅-钛酸铅为研究对象，利用拉曼散射光谱、透射光谱、马赫-曾德干涉等光学研究手段，在材料的相结构及相转换、能带结构和电光性能等方面展开了系统全面的研究。首先利用拉曼散射光谱对材料的相结构以及相转换进行设计研究。对准同型相界组分0.24PIN-0.43PMN-0.33PT单晶的拉曼光谱进行Gauss拟合得到一系列的拉曼模式，通过分析拉曼模式的数量推断出室温下，单晶为单斜相结构。通过测试单晶样品表面不同区域的偏振拉曼光谱，判断出该组分单晶不同单斜相（MA、MB和MC）共存。通过研究该单晶材料偏振拉曼光谱随温度变化情况，并根据拉曼谱线的移动及合并，判断出单晶材料的相变过程，单斜到四方的相变温度为85°C，四方相到立方相的相转换温度为200°C。同时根据拉曼峰强度的比值分析了相变过程单晶晶格振动及畴结构变化。通过XRD和TSDC分析了材料的相变过程，并研究了[111]_c极化0.24PIN-0.43PMN-0.33PT单晶介温曲线中，从67°C升高到82°C时，介电系数出现了不连续跳变显示了在此温区发生多次相变。最后通过分析电场诱导下的单晶的偏振拉曼光谱分析出了MB到MC单斜相结构的相变过程。对单畴单晶材料的能带结构及相关物理参数进行研究。将0.24PIN-0.49PMN-0.27PT单晶沿[111]_c方向极化成稳定的单畴状态，具有较高的光学透过率，可以达到64%左右。和多畴态准同型相界组分0.24PIN-0.43PMN-0.33PT单晶进行对比，多畴态单晶由于其畴壁对光的散射作用会导致透射率降低，通过透射率计算材料吸收系数，进而求出了单晶直接禁带宽度和间接禁带宽度，分别为3.18eV和2.96eV。通过测试变温透射率，将室温和居里温度以上透射率进行对比发现单晶室温下的透射率和顺电相时的透射率非常接近，表明单晶在室温下可以极化成稳定的单畴状态。最后运用椭偏仪测量了单晶的折射率，通过最小二乘法拟合出了单晶折射率的塞尔迈耶尔色散方程，并通过线性拟合折射率关系得出了色散方程的相关参数。优异的基本光学性质表明该单晶在光学器件领域有很大的应用潜力。全面研究不同组分单晶的电光系数张量以及电光系数的温度稳定性。利用偏光显微镜观测不同组分0.24PIN-（0.76-x）PMN-xPT单晶的畴结构，利用布儒斯特角法测量了各组分单晶的寻常光折射率n_o和非寻常光折射率n_e，同时制作压电振子测试了单晶材料的横向压电应变系数d₃₁。选用改进的马赫-曾德干涉系统测量了各组分单晶的电光系数。对于准同型相界组分的单晶，其沿着[001]_c方向极化后，得到的最大的有效电光系数高达204pm/V，而单畴态的单晶也具有较高的电光系数，均高于传统的电光晶体LiNbO₃。由此可计算出材料具有的较小半波电压，同时我们还发现单晶PIN-PMN-PT具有较好的温度稳定性。因此，高的电光系数、较小的半波电压以及较好的温度稳定性使得该单晶材料在特定的应用领域中可以替代传统的LiNbO₃晶体。实验证实对准同型相界组分单晶沿[011]_c方向极化可诱导出稳定的单畴态，而此单畴态具有优异的透光性能和较高的电光系数分量。更多还原

【Abstract】 Relaxor-based ferroelectric single crystals have been extensively studied due totheir extraordinary large electromechanical coupling coefficients （k33>90%）,piezoelectric coefficients （d33=1500-2500pC/N）, and excellent optical properties. Inrecent many years， the ternary xPb(In_1/2Nb_1/2)O₃-（1-x-y）Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃（PIN-PMN-PT） single crystal system has been developed, which has higherrhombohedral-tetragonal phase transition temperature and2times lager coercivefield than that of PMN-PT single crystals. Devices using the ternary single crystalcan work at high temperatures range and the single domain state can be more stable.More importantly, they have just as excellent piezoelectric properties as that ofPMN-PT single crystals. Based on optical research methods, we have performedsystematic investigations on phase structure, phase transition, energy band structure,and electro-optic properties of PIN-PMN-PT single crystals.Firstly, polarized Raman spectroscopy was performed to investigate the locallattice structure and phase transitions of unpoled0.24PIN-0.43PMN-0.33PT singlecrystal. Local lattice structure was investigated by Micro-Raman spectroscopy atroom temperature. A total of12Raman active modes were ascertained using theGauss line shape approximation, which deduces that0.43PIN-0.26PMN-0.33PTsingle crystal with morph tropic phase boundary （MPB） composition has monoclinicsymmetry. MA-, MB-and MC-type monoclinic phases were detected in differentmicro areas. Temperature dependence of Raman intensities, frequency shifts, modemerge and intensity ratios in the VV and VH geometries were investigated, theresults indicat that the monoclinic-tetragonal （M-T） phase transition occurs at85°C,which is verified by the mode merging from520cm^-1and580cm^-1to500cm^-1. Thetetragonal-cubic （T-C） phase transition happens at200°C based on the vanishingmode at780cm^-1measured in the VH polarization. The phase transition was alsoinvestigated by analyzing the temperature-dependent relative dielectric permittivityof both poled and unpoled0.43PIN-0.26PMN-0.33PT single crystal. The split of（200） and （002） peaks in detailed XRD spectra of0.24PIN-0.43PMN-0.33PT singlecrystal in the2θ range of44.6°-45.2°during heating from room temperature to200°C was also studied to confirm the phase transition. Several sharp peaks of thethermally stimulated depolarization current curve around the phase transitiontemperature from67to82°C arise in the sample poled along [111]_cdirection, whichis in accordance with the ‘step shape’ dielectric characteristic. MB-MCmonoclinicphase transition induced by electric field was studied. Optical transmission spectra of single crystal0.24PIN-（0.76-x）PMN-xPT（x=0.27,0.33） were measured in the pseudo-cubic crystallographic directions [111]_cand [112]_c. The ferroelectric domain structures were observed to explain thedifferences between the transmittances of the two composition crystals. Thewavelength dependence of the absorption coefficients was computed and the opticalenergy bandgaps were calculated for both direct and indirect transitions. Based onthe theory of band to band transitions, the direct and indirect energy gaps weredetermined to be E_gd=3.09³.18eV and E_gi=2.89².96eV, respectively, and thephonon energy is E_p=0.07⁰.08eV. The transmission spectra in transmission andabsorption regions were explained by the extinction coefficients measured byspectroscopic ellipsometry. Optical transmission spectra were recorded at both roomtemperature and200°C. The optical absorption edge at200°C has an obviousred-shift compared with that at room temperature, which indicates the change of thebandgap with temperature. Specifically, E_g=3.18eV and2.95eV, respectively, atroom temperature and200°C. The Sellmeier dispersion equation of n for0.24PIN-0.49PMN-0.27PT single crystal is calculated by fitting the experimentaldata. The parameters of room temperature Sellmeier oscillator were also calculated.Linear electro-optic properties of0.24PIN-（0.76-x） PMN-xPT single crystalswith compositions in rhombohedral, MPB and tetragonal phases have beeninvestigated. A very large effective electro-optic coefficientγ c（204pm/V） wasobserved when the crystal is poled along [001]_c with composition near the MPB.The rhombohedral phase （x=0.27and0.30） single crystals poled along [111]direction and tetragonal phase （x=0.39） single crystal poled along [001] directionhave excellent single domain state, and their electro-optic coefficients （γ c=76,94and43pm/V for the crystals with x=0.27,0.30and0.39, respectively） were found tobe much higher than that of traditional widely used electro-optic single crystalLiNbO₃（γ c=19.9pm/V）. The electro-optic coefficients of the rhombohedral singlecrystal were proved to have excellent temperature stability. The half-wave voltageVπ was calculated to be much lower （less than1000V） than that of LiNbO₃singlecrystal （2800V）. These excellent electro-optic properties make this kind of singlecrystal very promising for electro-optic modulation applications.更多还原