Study On The Influence Of Bismuth Titanate Template Size On The Properties Of Sodium Bismuth Titanate-based Piezoelectric Ceramics

Piezoelectric ceramics are widely used in sensors,transducers,actuators and other civil instruments as well as information functional materials in the military industry.As one of lead-free piezoelectric ceramics,sodium bismuth titanate-based（BNT）piezoelectric ceramics are considered to be the most likely to replace lead based piezoelectric ceramics due to their excellent electrical properties.At present,it is limited to improve the performance of BNT piezoelectric ceramics by adding new components and doping modification.However,preparing texturized ceramics with grain orientation using texturization technology is an effective way to improve the performance of lead-free piezoelectric ceramics.Therefore,this thesis focuses on BNT-based textured ceramics,which is expected to make a certain progress in the research and development of lead-free piezoelectric ceramics.In this thesis,the BNT-BKT binary system was used as the basic formula of research to study the preparation process of high-purity large-size flake bismuth titanate（Bi T）template grains.The BNKT-In texture piezoelectric ceramics were prepared by the reactive template grain growth method（RTGG）using different size Bi T template grains.Furthermore,the effects of sintering temperature on BNKT-75NT texture piezoelectric ceramics were then systematically investigated.Based on the demand for the preparation of high-purity large-size Bi T template grains,the effects of different molten salt systems on the purity of Bi T templates were firstly investigated.The results showed that only the Bi T template grains prepared by the KCl molten salt system were pure phase.The size of the template grains increased in both radial and thickness directions with the increase of the synthesis temperature and the extension of the holding time.The fine particles in the products were gradually reduced.Through process optimization,the high-purity large-size Bi T template grains with the size of 1.65～30.12μm,the average size of 7.92μm,the average thickness of 0.67μm,and the orientation ratio of11.82 were obtained by using KCl as the molten salt and holding at 1140℃for 8 h.Based on the above study,BNKT-In textured piezoelectric ceramics were prepared by the reactive template grain growth（RTGG）method using three different sizes of Bi T template grains as templates,and the effect of Bi T template grain size on the structure and properties of BNKT-In textured piezoelectric ceramics was systematically investigated.The results show that the template grain size has obvious influence on the piezoelectric properties of BNKT-In ceramics.With the increase of Bi T template grain size,the sample grain size,(9₃₃ and(9^*₃₃ all showed an increasing trend.The textured ceramics prepared by using large size template grains have excellent comprehensive properties.When the sintering temperature is 1160℃,the piezoelectric constant of the textured ceramics with large template(9₃₃=286 p C/N,the maximum bipolar strain value reaches 0.51%@5 k V/mm,the inverse piezoelectric constant(9^*₃₃=1116 pm/V at 4 k V/mm electric field strength were obtained.Compared with piezoelectric ceramics prepared by solid-phase method under the same processing conditions,its(9₃₃ is improved by 78%,and its(9^*₃₃ is improved by 1.82times.In order to further improve the inverse piezoelectric properties,based on the study of BNKT-In textured ceramics,large-size template grains（Bi T template grains held at 1140℃for 8 h）were selected as templates,and equal amounts of niobium and tantalum co-doped BNKT-75NT textured ceramics were prepared by the RTGG method.The results showed that the sintering temperature has obvious influence on the structure and properties of the samples.When the sintering temperature is 1140℃,the BNKT-75NT ceramics prepared by textured method show excellent properties:(9₃₃=63 p C/N,and the maximum bipolar strain value is 1.02%@7 k V/mm,(9^*₃₃=1724 pm/V@5 k V/mm.Compared with ceramic by the solid phase method,the(9^*₃₃ performance was improved by 1.14 times.The(9^*₃₃ and strain of the ceramics are comparable to BNT-based single crystal.The results indicated that high-purity and large-size Bi T template grains can significantly improve the maximum strain and(9^*₃₃ of BNKT piezoelectric ceramics,which are expected to be used to improve the piezoelectric properties of other BNT-based piezoelectric ceramics.