| PIN-PMN-PT single crystals have drawn a lot of attention both in scientific research and industry because of ultrahigh piezoelectric and electromechanical properties. Piezoelectric devices based on Pb Ti O3 system single crystals, such as sensors and transducers, have been widely reported. Ternary PIN-PMN-PT single crstals have enhanced thermal and electric field stabilities. In order to further widen the application range, a new generation, PIN-PMN-PT:Mn single crystals, has been successfully grown for high power devices. The positive experiences of PIN-PMN-PT single crystals are driving the development of new piezoelectric single crystals. In recent years, the demand on environment-friendly materials is increasing along with the rising sense of environment protection.(K, Na)Nb O3(KNN) family piezoelectric materials have been considered as one of the most promising candidates to replace relaxor-Pb Ti O3 piezoelectrics and KNN based single crystals have obtained more and more attention. However, the growth and properties of the KNN based crystals have not been development significantly. In this work, various composition and large size KNN based crystals have been successfully grown. The piezoelectric, ferroelectric, dielectric properties for the PIN-PMN-PT:Mn, KNNTL and KNNTL:Mn single crystals were comprehensively investigated to study the effect of Mn modifying. The source of high piezoelectric responses for the two families were studied by analyzing their intrinsic and extrinsic contributions.KNNTL single crystals and KNNTL:Mn single crystal were growth by top-seeded solution growth method. Large sizes of the as-grown single crystals allowed comprehensive investigation of the KNN based crystals. Co mpositions and compositional uniformity of the single crystals were checked by energy dispersive spectroscopy. Temperature dependence of dielectric constant and X-ray diffraction patterns were compared to check the phase structures and relaxation properties of those single crystals. The relation between Ta content and the phase structures and relaxation was investigated for the KNNTL single crystals.Complete stets of elastic, dielectric and piezoelectric coefficients for KNNTL, KNNTL:Mn and three composition PIN-PMN-PT:Mn single crystals were determined to investigate the effect of Mn modifying. After introduction of Mn element, both of the two systems became “harder” and their dielectric properties were found to be decreased. The piezoelectric properties of PIN-PMN-PT:Mn single crystals were also decreased compared with the pure PIN-PMN-PT single crystals. However, the properties of KNNTL:Mn single crystals were influenced both by the introduction of Mn and by the orthorhombic-tetragonal polymorphic phase transition(PPT) temperature shifting. The piezoelectric coefficients of KNNTL:Mn single crystal were found to be higher because its PPT temperature was closer to room temperature. The electromechanical coupling factors k33 of KNNTL:Mn single crystals was found to be the highest(~95%) in piezoelectric materials. The coefficient d33 was improved to be 545 p C/N, the highest in KNN based piezoelectric materials, by optimizing the compositions. PIN-PMN-PT:Mn single crystals in orthorhombic phase had excellent shear piezoelectric and electromechanical properties. The coefficient d15 and d24 were found as high as 3100 p C/N and 2400 p C/N, respectively. PIN-PMN-PT:Mn single crystals in rhombohedral phase presented excellent longitudinal and shear properties and the co rresponding d15 and k15 were found to be 2980 p C/N and 92%, respectively. Through comparing the properties of Mn doped and undoped KNNTL and PIN-PMN-PT single crystals, it is found that the effect of Mn modifying are very similar, but slightly different.The variations of ferroelectric properties, mechanical quality factors and extrinsic contributions were studied for the before and after Mn doped KNNTL and PIN-PMN-PT single crystals. Internal biases were found both in the KNNTL:Mn and PIN-PMN-PT:Mn single crystals. Meanwhile, the mechanical quality factors were found to be increased and extrinsic contributions were found to be decreased by the modifying of Mn ions in KNNTL and PIN-PMN-PT single crystals. The Mn dopants will generate oxygen vacancies. These oxygen vacancies realign themselves during the poling process along the preferential direction of the spontaneous polarization and give rise to the internal bias, which clamps the domain wall motions and decrease the activity of domain wall. Of particular i mportance is that, the extrinsic contributions for KNN based and relaxor-Pb Ti O3 based single crystals cannot be neglected. The extrinsic contributions of orthorhombic phase PIN-PMN-PT:Mn and KNNTL:Mn single crystals were above 10% at 1k V/cm and it was as high as 22% in KNNTL66/34 single crystals. The extrinsic contribution is an important source of high piezoelectric responses. It is very significant to study the intrinsic and extrinsic contributions for improving the piezoelectric properties. |
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