| The relaxor-based ferroelectric single crystals are a kind of complex solidsolutions, including lead zinc niobate-lead titanate (PZN-PT) and lead magnesiumniobate-lead titanate (PMN-PT), they have attracted a lot of attention in recent yearsdue to their excellent piezoelectric, ferroelectric and acoustic properties. They arealso interesting subjects of fundamental studies, particularly for the morphotropicphase boundary (MPB) composition, in which different phases can coexist. Thephysical and chemical properties of crystals always depend on their microstructures.The loss properties of the crystal, such as dielectric loss, mechanical loss andpiezoelectric loss, are related to the domain wall contribution. The study of the lossproperties of relaxor-based ferroelectric single crystal can contribute to theunderstanding of correlation between ferroelectric domain structure andelectromechanical properties of the crystal, as well as the origin of largepiezoelectric effect.The complex electromechanical coefficients can be detected based on fivecharacteristic parameters. The complex coefficients of PZT-5H ceramic andPMN-0.29PT single crystal have been detected, it was found that PMN-0.29PTsingle crystal appears to have small dielectric loss factor, but the mechanical lossfactor is as large as that of PZT-5H ceramic. In addition, high frequencypiezoelectric vibrator of [001]cpoled PMN-0.29PT single crystals have much largermechanical loss factor than that of low frequency piezoelectric vibrator.There are two types of ferroelectric domain in relaxor-based ferroelectricsingle crystal: non-180°domain and180°domain. The non-180°domain contains71°domain,109°domain and90°domain. The correlation between piezoelectricproperties and domain switching was observed by polarizing light microscopy, itwas found that there is no direct180°domain switching during the poling. Instead, two or more consecutive non-180°domain switching is the primary route toaccomplish the poling. The poling field dependence of loss properties inPMN-0.38PT and PMN-0.30PT single crystal were studied based on complexcoefficients determination. It was found that the mechanical loss factor ofPMN-0.38PT single crystal increases in the poling process, but the dielectric lossfactor decreases when the poled field increased. The poled field dependence of lossproperties in PMN-0.30PT was studied, it was found that the crystal can be poledinto mono-domain structure, and the dielectric and mechanical loss factors becomevery small. Based on the experimental results, the dielectric and mechanical lossfactors of the crystals are originated from different domain structures.More recently, it has been reported that lead indium niobate-lead magnesiumniobate-lead titanate (PIN-PMN-PT) single crystals have higher coercive fields andhigher depoling temperatures than that of the corresponding binary PMN-PT singlecrystals, which can be used for large field drive piezoelectric devices at a widerrange of temperature. The PIN-PMN-PT single crystals were poled along differentdirections, then the correlation between dielectric properties of the crystal andtemperature was studied. It is found that the intermediate phase can be induced inPIN-PMN-PT single crystal near the MPB compostion, which is similar to theproperties of PMN-PT single crystal with MPB composition. The high piezoelectricproperties may be from reasons such as non-180°domain rotation etc, that arerelated to the co-existence of multiphases. The correlate of the piezoelectricproperties of [011]_cand [111]_cpoled PIN-PMN-PT single crystal and temperaturewas studied. It is found that the [011]_cpoled PIN-PMN-PT single crystal hasexcellent and transverse piezoelectric properties. The temperature dependence ofpiezoelectric properties changed slightly when the temperature is lower than thedepoling temperature TR-T. The [111]_cpoled PIN-PMN-PT single crystal also hasexcellent shear piezoelectric property, but the properties change drastically with temperature, so it is not good for piezoelectric transducer. |
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