Research On DC Field Induced Pyroelectric Effect And Application Of Lead Zirconate Stannate Titanate Based Antiferroelectric Ceramics

Lead zirconate stannate titanate （PZST） based antiferroelectric ceramics was widelyused in high strain actuators, shock-activated energy transducer and high-density capacitorowing to their outstanding field induced phase transitions and adjustable dielectric andpiezoelectric properties. In addition, PZST based antiferroelectric material was seen as oneof the important alternative materials used in infrared detector because of its dcfield–induced dielectric enhancement effect. Therefore, this article conducted a systematicresearch on the dc field-induced pyroelectric effect of PZST based antiferroelectric throughthe selection of the material system, the improvement of machinability and pyroelectricproperties, the broadening of temperature zone and the decrease of the Curie temperature tosolve the bad machinability and pyroelectric properties, narrow temperature zone, highCurie temperature and other problems of PZST based antiferroelectric ceramics used inuncooled infrared detectors. Furthermore, the feasibility of low temperature sinteringantiferroelectric with high pyroelectric properties was discussed and thus laying a basis fordeveloping thick film based uncooled infrared detectors.This article discussed about La-doped PZST based antiferroelectric ceramics withwide FE-AFE adjustment range near the phase boundary. On this basis, the dielectric andferroelectric properties of La-modified Pb_0.9-xLa_2x/3Ba_0.1(Zr_0.7Sn_0.22Ti_0.06)O₃were studied,the impact of La content on the dc field-induced pyroelectric properties of antiferroelectricceramics was investigated. Then, we studied the influence of the dc electric field ondielectric constant and dielectric loss of antiferroelectric ceramics and ferroelectricceramics with different Zr/Ti near FE/AFE phase boundary to reveal the mechanism of thedc field–induced dielectric enhancement effect of antiferroelectric ceramics, andconsequently the best pyroelectric effect was achieved by modifying the composition ofantiferroelectric.In order to solve the problem that the machinability and the pyroelectric propertieswere greatly reduced by the volatilization of lead during sintering, excessive PbO wasadded when antiferroelectric ceramics was prepared. The impacts of excessive PbO on the crystal structure, microstructure, dielectric and dc-induced pyroelectric properties ofantiferroelectric ceramics were explored. Experiments indicated that the density and thedc-field induced pyroelectric properties of antiferroelectric ceramics were greatly improvedbecause the pyrochlore phase decreased when excessive PbO was added. The pyroelectriccoefficient of7500μC/m²K under an800V/mm dc bias field was obtained inantiferroelectric ceramics with9wt%excessive PbO, and good density and pyroelectricproperty were beneficial for the development of infrared detectors.Antiferroelectric ceramics with wide pyroelectric temperature zone was prepared bythe composition and structure designs, so as to solve the problem that the pyroelectrictemperature zone was too narrow when antiferroelectric was used in uncooled infrareddetectors. Because the activity of the powder was relatively low, it was not easy to react afterit was pretreated at a high temperature. Hence, antiferroelectric multi-phased ceramic withtwo pyroelectric peaks was prepared by mixing two different antiferroelectric powders.Antiferroelectric multi-phased ceramics composed of two compositions and threecompositions with20-50℃pyroelectric temperature zone and figure of merit of2×10^-5Pa^-0.5under a400V/mm dc bias field by inserting divided layer to prevent thereacting of powder when antiferroelectric ceramics was prepared.With a view to solve the problem that the curie temperature of antiferroelectricceramics was higher than the temperature of using uncooled infrared detector, Ba²⁺with theouter electron cloud of inert gas-type placing Pb²⁺with the outer electron cloud structure ofnon-inert gas type was used to decrease the curie temperature of antiferroelectric ceramics.The impact of Ba²⁺content on the ferroelectric, dielectric and the dc field-inducedpyroelectric properties were studied and the laws of dielectric properties of antiferroelectric,ferroelectric ceramics undergoing a first-order phase transition and ferroelectric ceramicsundergoing a second-order phase transition were revealed. Because the less the tolerancewas and the more stable the antiferroelectric became, antiferroelectric ceramics with highpyroelectric properties near room temperature was prepared by Mn ion with large ionicradius placing Ti ion with small ionic radius. The figure of merit of25×10^-5Pa^-0.5under a500V/mm dc bias field was obtained in (Pb_0.832Ba_0.138La_0.02)(Zr_0.7Ti_0.05Sn_0.24)O₃antiferroelectric ceramics with0.2mol%Mn doping and the large figure of merit near room temperature provided a basis for antiferroelectric materials used in uncooled infrareddetector.To find a solution to the problem that antiferroelectric ceramics could not be used inthick-film based uncooled infrared detector because of its high sintering temperature,antiferroelectric ceramics was prepared at a low sintering temperature by using PbO-B₂O₃glass as a sintering aid. The relationship between crystal structure and dielectric, dc fieldinduced pyroelectric properties was known and antiferroelectric ceramics with highpyroelectric properties was prepared by probing into the impacts of addition of glass,sintering time, and glass with different PbO content on the microstructure, dielectric,ferroelectric and dc-field induced pyroelectric properties. The pyroelectric coefficient of5835μC/m²K and the figure of merit of21.59×10^-5Pa^-0.5under a700V/mm dc bias fieldwere obtained in Pb_0.87Ba_0.1La_0.02(Zr_0.65Sn_0.28Ti_0.07)+6wt%PbO with1wt%0.5PbO-0.5B₂O₃glass and9h sintering time. The pyroelectric coefficient of9050μC/m²K and thefigure of merit of20.7×10^-5Pa^-0.5under a600V/mm dc bias field were obtained inPb_0.87Ba_0.1La_0.02(Zr_0.7Sn_0.24Ti_0.06)+6wt%PbO with1wt%0.8PbO-0.2B₂O₃glass and12hsintering time.