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Preparation and Electric Properties of Lead-Free Sodium Potassium Niobate Based Piezoceramics

Author: LiLu
Tutor: GongYueQiu
School: Xiangtan University
Course: Materials Physics and Chemistry
Keywords: Solvothermal synthesis KNN Ta-doping Sb-doping Piezoelectric properties
CLC: TM282
Type: Master's thesis
Year: 2011
Downloads: 140
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Abstract


As new type functional materials, piezoelectric ceramics can realize the convertion between electric energy and mechanical energy and have wide applications. Conventional Pb-based piezoceramics include poisonous metallic element lead and can not meet environmental protection. Therefore, it is urgent to look for lead-free piezoelectric materials to replace lead-based materials. In this paper, from environment protection perspective, Ta （Sb）-modified sodium potassium niobate （KNN） lead-free piezoelectric materials were prepared by solvothermal and conventional solid-state reaction methods, respectively. The phase structures, surface morphologies and electric properties of these samples were studied in detail. The main research contents are as follow:In the first part, the preparation of tantalum （Ta）-doped KNN ((K0.5Na0.5)(Nb1-xTax)O3, KNNTx （x = 0～0.4）) powders was investigated firstly under hydrothermal and solvothermal conditions, respectively. The results of XRD and SEM showed that KNNTx powders with perovskite structure, regular morphology and small grain size were obtained at 180 oC by solvothermal method. However, under hydrothermal conditions, the reaction could not be carried out at the same temperature. Secondly, these powders were transformed into corresponding ceramics by normal sintering. The optimal sintering temperatures of ceramics rised gradually as the increase of Ta doping content. The optimal heating rate and holding time were 5 oC/min and 4 h, respectively. Thirdly, it was found that sintering temperature and poling condition had a great influence on piezoelectric properties of KNNTx ceramics. The maximum piezoelectric constant d33 value was obtained for KNNT0.3 ceramics （156 pC/N）. Lastly, compared with conventional solid-state reaction technique, solvothermal method could reduce sintering temperature obviously and improve piezoelectric properties of KNNTx ceramics to some extent.In the second part, the synthesis of stibium （Sb）-doped KNN ((K0.5Na0.5)(Nb1-ySby)O3, KNNSy （y = 0.02～0.10）) powders, the sintering process and piezoelectric properties of corresponding ceramics were investigated. The results of XRD and SEM showed that Sb-doped KNN powders were synthesized successfully at 220 oC by solvothermal method. The optimal sintering temperatures of ceramics also rised with the increase of Sb doping content. The microstructures of ceramics were affected markedly by sintering temperature and holding time. By analysis of the factors of affecting piezoelectric properties of KNNSy ceramics, enhanced piezoelectric performance could be obtained by selecting optimal sinering condition or poling temperature near the orthorhombic-tetragonal polymorphic phase transition temperature region. The maximum d33 value was obtained for KNNS0.06 ceramics （134 pC/N）. It was also found that the piezoelectric properties of KNNSy ceramics were degraded after a period of time （called aging）. It resulted in the instability of piezoelectric properties of ceramics.This paper shows that solvothermal process is a new synthetic method which can prepare KNN-base piezoelectric materials under relatively low reaction temperature. Doping （Ta or Sb） can improve piezoelectric properties of KNN ceramics dramatically. Sintering and poling condition have an obvious influence on piezoelectric properties. Therefore, the mentioned above effect factors need to be considered synthetically to further improve the piezoelectric properties of KNN-based ceramics.

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CLC: > Industrial Technology > Electrotechnical > Electrical materials > Electric and ceramic materials > Piezoelectric ceramics
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