Synthesis,Sintering,Film Deposition And Electrical Properties Of Barium Calcium Zirconate Titanate Ultra-fine Powders

As a novel environmentally-friendly lead-free material,barium calcium zirconate titanate[(1-x)Ba Ti_0.8Zr_0.2O₃-x Ba_0.7Ca_0.3Ti O₃,referred to as BCZT],has excellent piezoelectric properties,which is equal to the traditional lead-based materials.Highly active powder is the premise and foundation for the preparation of high-performance BCZT bulks.However,the conventional solid-state reaction method has problems such as high reaction temperature,long synthesis time,and composition deviation from stoichiometric ratio.In this dissertation,wet chemical method was used to synthesize BCZT ultra-fine powders,and the synthesis process,reaction mechanism,sintering activity and electrical properties were studied.On this basis,the deposition of BCZT epitaxial films was explored,in order to provide a preferred method for the synthesis of highly active BCZT powders,and offer a new kind of environmentally-friendly functional materials with good properties,which could improve the piezoelectric properties of BCZT bulks further and meet the development needs of piezoelectric device integration.Through the improved sol-gel method,the BCZT powders with accurate stoichiometric ratio,uniform composition distribution,and fine particles(average particle size about 105 nm)were successfully synthesized at a calcination temperature of 800? by replacing the traditional inorganic zirconium source with the organic zirconium source.Compared with the conventional solid-state reaction method,the synthesis temperature could be reduced by about 550?.By combining the sol-gel method with the hydrothermal method,the synthesis temperature of the BCZT powders was greatly reduced,and the low temperature(180?)synthesis of ultra-fine powders was successfully realized.Also,the effects of the sol-gel-hydrothermal synthesis process on the phase structure and micromorphology of BCZT powders were studied,and the results showed that the synthesis temperature had a great influence on the phase structure,the micromorphology and the particle size of the powders.Moreover,with the extension of the synthesis time or the decrease of the concentration of the alkaline solution,the particle size of the powders increased gradually.The suitable synthesis condition was determined as:synthesis temperature 180?,synthesis time 12h,alkaline solution concentration 4M.Under this condition,the average particle size of the obtained BCZT powders was about 93nm.Based on that,by controlling the synthesis temperature and synthesis time of the microwave-assisted sol-gel-hydrothermal method,the introduction of microwave could further realize the rapid synthesis of BCZT ultra-fine powders at a low temperature,and the synthesis time could be decreased to 60min.Compared with the hydrothermal method or sol-gel-hydrothermal method,the synthesis time could be shortened by about 10h.Moreover,the BCZT powders synthesized under this condition had a perovskite structure,uniform composition,good crystallization and narrow particle size distribution,and the average particle size of the obtained powders was about 85nm.The process of these three wet chemical methods was comprehensively compared.By comparing the phase structure and micromorphology of the BCZT ultra-fine powders,the synthesis mechanisms were analyzed.The results showed that,the wet chemistry method,such as sol-gel method,could effectively shorten the diffusion distance between the ions of each component during the reaction,making the mixing of ions in the liquid phase more uniform,so as to ensure the uniform and accurate ingredients,promote the reaction between ions during calcination and further reduce the calcination temperature effectively;In addition,under the"low temperature and high pressure"environment provided by hydrothermal synthesis,the ions grew into crystals through the"dissolution-crystallization"process,which could further reduce the crystallization temperature;Moreover,the introduction of microwave could provide a"rapid heating"environment,so as to enhance the reaction efficiency and shorten the reaction time together with the"low temperature and high pressure"hydrothermal environment.The BCZT ultra-fine powders synthesized by the improved sol-gel method,sol-gel-hydrothermal method and microwave-assisted sol-gel-hydrothermal method were respectively sintered at 1400? through atmospheric pressure sintering.Besides,the sintering activity,as well as the electrical properties,was compared.Compared with conventional solid-state reaction method,the BCZT powders synthesized by wet chemical method,especially by microwave-assisted sol-gel-hydrothermal method,had a better sintering activity.The sintered bulks had a denser structure and better electrical properties:d₃₃=496 p C/N,2P_r=25.63?C/cm²,?=9579.Also,these bulks could be obtained at a lower reaction temperature and shorter synthesis time,which can effectively shorten the preparation cycle and reduce the production cost.Furthermore,the results also showed that the component ratio of raw material also had a great impact on the structure and properties of BCZT materials.When x was 0.5,BCZT materials exhibited better electrical properties,which is mainly due to the morphotropic phase boundary(MPB)structure of the coexisting between rhombohedral phase and tetragonal phase at room temperature.The high-density sintering bulks prepared from the BCZT ultra-fine powders by microwave-assisted sol-gel-hydrothermal method with a component ratio of x=0.5were used as the targets to deposited BCZT films by pulse laser deposition(PLD).By controlling the process parameters(deposition temperature and oxygen partial pressure),BCZT films with preferred orientation and epitaxial growth were deposited successfully.On this basis,BCZT films were deposited on the substrates with different orientations of(001),(110)and(111),and the effects of film orientation on their structure and electrical properties were studied.The results showed that,with the increase of deposition temperature and oxygen partial pressure,the crystallinity of BCZT epitaxial films increased gradually and the electrical properties improved constantly.The suitable synthesis condition was determined as:deposition temperature650?,oxygen partial pressure 15 Pa.Under this condition,the obtained BCZT epitaxial films had perovskite structure phase,good crystallinity,flat and dense surface,and showed excellent electrical properties(2P_r=22.91?C/cm² and the leakage current density was 1.44×10^-3 A/cm²).This also suggested that the BCZT ultra-fine powders synthesized by the microwave-assisted sol-gel-hydrothermal method could be a kind of high-quality raw materials for targets during PLD process.Furthermore,the preferred orientation of the films also had a great impact on the properties.Compared with the(110)and(111)orientation,the(001)oriented BCZT films had better electrical properties,which was mainly related to the spontaneous polarization vector lying in the[001]crystallization direction.