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Potassium bismuth sodium titanate based lead-free piezoelectric ceramics and its modification

Author: YangQingQing
Tutor: LiQuanLu
School: Shaanxi Normal University
Course: Condensed Matter Physics
Keywords: sodium bismuth potassium titanate sintering temperature dielectricproperties piezoelectric properties
CLC: TM282
Type: Master's thesis
Year: 2013
Downloads: 31
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In this paper, the piezoelectric crystals and piezoelectric effect and ferroelectric crystal and ferroelectric was discussed. Five kinds of main lead-free piezoelectric ceramics and its structure characteristics are summarized. The main performance parameters of piezoelectric ceramics and the main application of two aspects of piezoelectric ceramics in piezoelectric vibrator and piezoelectric transducer were introduced. The experimental process of traditional solid-state reaction method and the performance testing approach of ceramic were studied, then the best preparation conditions of the ceramic were determined, and the piezoelectric properties were investigated.This paper studied two experiments.Firstly, the Bi0.5(Na1-xKx)0.5TiO3(BNKT) lead-free piezoelectric ceramic was made by introducing BKT(tetragonal phase) into BNT-based(rhombohedral phase) solid solutions, and the piezoelectric properties of BNKT which in the range of morphotropic phase boundary (MPB) were researched. Next, LiNbO3was introduced respectively on the basis of BNKT and (1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xLiNb03((1-x) BNKT-xLN) ceramic was synthesized, then the effect of sintering characteristic and piezoelectric properties for (1-x) BNKT-xLN ceramic were studyed.In this experiment, the solid-phase sintering process is used to make the Bi0.5(Na1-xKx)0.5TiO3ceramic samples, in which the process parameters set as follows, samples calcined at800℃; sintered at1150℃, holding time is120min, heating rate2.5℃/min; the temperature, voltage and time of polarization process were set to120℃,4kv/mm,25min. The influences of different BKT contents on the crystal structure, microstructure and electrical properties of BNKT ceramics were studied:(1) XRD analysis shows that, with the increasing of the BKT contents, all the ceramics are pure perovskite phase solid solution, at the same time, the peaks of the XRD patterns move toward the lower angles, indicating the expansion of the unit cell volume. When BKT content equals to0.2, the morphotropic phase boundary (MPB) of the BNKT binary ceramics was identified, in which rhombohedral phase coexists with tetragonal phase.(2) The SEM photographs show that, The grain size first decreased and then increased with the increasing BKT content, indicating that the substitution of K+can refine the grains and improve the sintering properties of the ceramics.(3) In the MPB composition, the piezoelectric constant33and electromechanical coupling factor KP reached the maximum value. Wth an increase of the BKT contents, the dielectric constant ε33/T/ε0and mechanical quality factor Qm of ceramic samples sharply increase and reduce, respectively.The (1-x)Bi0.5(Na0.8K0.2)0.5TiO3-xLiNbO3((1-x) BNKT-xLN for short) system ceramics can be synthesized by a way of LiNbO3doping in the MPB composition of BNKT ceramic. Studying the influence of sintering temperature to the density and the radial shrinkage, the best sintering temperature is intended to1130℃for (1-x) BNKT-xLN system ceramics. The result indicated that the addition of LiNbO3significantly improved the sintering temperature performance, meanwhile, its sintering temperature was reduced obviously. The impact of different doping of LiNbO3on this system ceramics summarized as follows:first, when mixed with a small amount of LiNbO3in BNKT,(1-x) BNKT-xLN can form a solid during sintering, but too much, it can be seen some secondary impurity phases. Second, it can be observed from the SEM photographs that the grain sizes of ceramics increase by increasing amount of LiNbO3addition. finally, when x equals to0.01, the best piezoelectric properties are realized.Furthermore, it can be seen that the dielectric constant ε33/T/ε0and dissipation factor tan δ slightly are evidently increased almost in the same trend with increase of LiNbO3addition.

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