| 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(In1/2Nb1/2)O3-（1-x-y）Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)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 Egd=3.093.18eV and Egi=2.892.96eV, respectively, and thephonon energy is Ep=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, Eg=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. |
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