| Bismuth-based perovskite-structured solid solution materials can exhibit electric field induced giant strains through appropriate compositional modification or temperature modulation, being expected to become one type of novel ceramic materials for the application of displacement actuators. Recently, as a large number of research works have been put into the (Bio.5Nao.s)Ti03-based material systems, Bi(Mgo.5Tio.5)03 (BMT), (Bio.5Ko.5)Ti03 (BKT) and BiFeO3 (BF)-based material systems have attracted more and more attention. According to the current reports, the characteristics of electrostrain, including its driving electric field, temperature stability, frequence sensitivity and hysteresis, all show distinct features in different material systems. In order to conduct more in-depth investigations and better comparative analyses and to find out the similarities and differences of electrostrains for different systems, it is necessary to explore new bismuth-containing perovskite systems and especially to carry out a comprehensive study focusing on its electrostrain. Considering the structure stability and difficulty of processing for different materials among the Bi(Me Me)O3 (Me=Mg, Zn, Ni; Me=Ti, Nb, W) systems, (1-x)BiCMg3/4W1/4)O3-xPbTiO3 ((1-x)BMW-xPT) binnary system and (l-x)(0.38 Bi(Mg2/3Nb1/3)O3-0.62PbTiO3)-xBaZrO3 ((1-x)(0.38BMN-0.62PT)-xBZ) ternary system were constructed in this work and their synthesis, compositional modulation, phase-structural as well as electric properties evolutions and especially its electrostrain performances were systematically investigated. The main contents were outlined below:(1) Binary system (1-x)BMW-xPT piezoelectric ceramics were prepared by a conventional solid state method, and its phase structural, dielectric, piezoelectric, ferroelectric and electrostrain properties evolutions were systematically analyzed as a function of the PT content. The results demonstrated that this binary system underwent a phase structural transformation from a pure pseudocubic phase to a single tetragonal phase as the PT content increasing, which was found to be accompanied by a relaxor-normal phase transition. In addition, the morphotropic phase boundary (MPB) was formed in the composition range of 0.625<x<0.64, in which an imtermediate Ma phase was discovered by means of high-resolution synchrotron X-ray powder diffraction, and thus the quasi-static piezoelectric constant could reach a maximum value of 310 pC/N as x=0.63. Moreover, it is worth noting that an extremely large electromechanical strain up to 0.45% with a low hysteresis of 33% could be generated under a high bias field in the sample of x=0.615 with coexisted ergodic and nonergodic phases. The generation of such a gaint strain was ascribed to the accumulated effects of field-induced continuous and reversible phase transition from an ergodic phase to a complete polar phase, and the intermediate phase induced by external fields makes the strain hysteresis of this system to be smaller than other bismuth-based systems owing to reduced energy barriers.(2)(1-x)(0.38BMN-0.62PT)-xfiZ ternary system was constructed by utilizing BZ substituted BMN and PT at the same time, and the evolutions of its phase structure, dielectric, piezoelectric, ferroelectric and electrostrain properties were systematically analyzed as a function of the BZ content. The results of XRD indicated that a compositional modulated phase structural transformation from a single tetragonal phase to a pure pseudocubic phase was happened as increased the BZ content. The MPB between tetragonal and pseudocubic phases could be identified roughly in the composition range of 0.05<x<0.075, and the quasi-static piezoelectric constant reached a maximum value of 280 pC/N as x=0.07. Besides, the experimental measured results suggested the electric porperties of this system were strongly composition-dependent, and the above phase structural transformation was found to be accompanied by a ferroelectric-nonergodic-ergodic phase transition. The electromechanical strain performances were markedly improved in the coexistence zone of ergodic and nonergodic, and the maximum strain of 0.42% could be obtained in the sample of x=0.08 under 7 kV/mm. |
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