【作者】 周宗辉；

【导师】 杜丕一；

【作者基本信息】 浙江大学 ， 材料学， 2005， 博士

【摘要】 热释电型非致冷焦平面阵列（Uncooled Focal Plane Array—UFPA）红外探测器件的特性直接与所用热释电材料相关,而热释电材料在居里温度点附近由于强介电峰的出现而具有最佳的热释电性能,可以获得较大的探测优值。因而,受热释电材料影响,这种探测器对使用环境温度有较高的要求。因此,开发一种复合热释电材料,使其在一定温度范围内具有多个强的介电峰,既可利用材料的复合效应,使材料具有高的热释电响应,又可拓宽其工作温度范围,降低探测器对使用环境温度的要求对热释电红外探测器,特别是红外热像仪性能的突破,具有重要意义。 本论文的研究目的在于对两种本身具有高热释电性能的钛酸锶钡Ba_l-xSr_xTiO₃（BST）和铌酸锶钡Sr_xBa_1-xNb₂O₆（SBN）材料进行两相复合共存的制备研究,获得高性能两相共存复相体系,为开发新型高性能热释电探测器打下基础。本研究主要利用传统原位烧结合成方法,通过新的复相形成控制理念,进行特殊配方设计控制,以原位合成方法制备复相陶瓷B_0.7S_0.3T_1-yN_y并获得钙钛矿/钨青铜两相共存的高热释电性能复相体系;通过深入研究两相共存体系中两相间的影响机制,掌握体系介电性能、热释电性能与结构、晶相间的关系,实现对热释电性能的调整、控制和提高。 本文全面回顾了UFPA,热释电材料以及复相陶瓷材料的研究进展,比较了各种UFPA的优缺点,总结了常用热释电材料及复相陶瓷材料的性能和制备方法。用XRD、SEM、EDXA、阻抗分析仪和热释电测试系统等分析了BST/SBN复相陶瓷B_0.7S_0.3T_1-yN_y的制备、微观结构、介电和热释电性能。对两相共存形成的机理,对复相陶瓷材料介电常数的混合法则在B_0.7S_0.3T_1-yN_y中的应用,对复相体系介电和热释电性能的产生和提高进行了详细研究。具体研究内容及研究结论如下: （1）对钙钛矿/钨青铜复相材料的形成和制备进行了研究。首次通过对组成的过量设计确定了B_0.7S_0.3T_1-yNy组成配方体系,对体系中形成钙钛矿相BST或钨青铜相SBN的剩余物含量及第二相形成量进行了详细的对比计算,从理论上证明了第二相的形成直接与剩余物含量相等。发现了,复相陶瓷的形成,两相的存在关系,直接与系统组分的过量相关。在形成以钙钛矿为主相的B_0.7S_0.3T_1-yN-y体系中,控制Nb₂O₅的过量可以控制形成第二相钨青铜相;在形成以钨青铜为主相的B_0.7S_0.3T_1-yN_y体系中,控制BaO和SrO的过量可以控制形成第二相钙钛矿相。B_0.7S_0.3T_1-yN_y体系中组分变化在y值为浙江大学博士学位论文摘要0.1⁰.8范围时可控制钙钦矿BsT相和钨青铜SBN相两相稳定共存,当y=0.3一0.4时,两相含量相当。 （2）对复相陶瓷原位形成两相的晶相特性进行了研究。确定了复相陶瓷B0.7503TI.尹y同时具有钙钦矿BST相和钨青铜SBN相两相复合的特性,形成的钙钦矿相和钨青铜相可以是分别掺杂有一定量NbZOS和Tio:的BST/NbZos和sBN/TIOZ固溶体相,也可以固溶量极少。两相含量相当的B0.7s03TI一热复相体系中形成的钙钦矿相几乎不固溶Nb205,而形成的钨青铜相则固溶有一定量的TIOZ。钨青铜相的铁电顺电相转变温度与钨青铜相中固溶TIOZ量相关,TIO:固溶量增加,转变温度降低;同时受复合体系中钙钦矿相的影响,钙钦矿相含量增加,转变温度升高。复相体系中钨青铜相的最低铁电顺电相转变温度约在200oC,比纯SBN相下降约90oC。 （3）对复相陶瓷B07S03TI.尹y的微观形貌进行了分析研究。研究表明,复相陶瓷BO.7SO.3TI令Ny体系明显由钙钦矿相和钨青铜相两相晶粒复合而成。钙钦矿相呈多边形小晶粒,而钨青铜相以长棒状大晶粒存在。钨青铜相晶粒的力学性能比钙钦矿相差,样品断裂时多为穿晶开裂。Nb介在钙钦矿相中固溶引起晶格较大畸变,阻碍钙钦矿相晶粒生长;较小晶粒的钙钦矿相存在及Ti4+在钨青铜相中固溶则抑制钨青铜相晶粒异常长大。与单相SBN陶瓷相比,小晶粒BST对大晶粒SBN空隙的填充,明显提高了复相陶瓷的致密度。 （4）对原位复合形成的B07so.3TI一y两相共存复相材料的介电常数与复合两相特性的关系进行了研究。研究指出,原位复合形成的BO.7s03TI浏y两相共存复相材料,不能简单地用传统的复相材料介电常数计算时考虑的仅与复合各单相本身的介电常数及其各自在复相体系中的含量有关进行讨论,而必须同时考虑到由于在同一体系中两相分别形成相关联的固溶体,并随着固溶度的不同分别对各相介电常数产生的影响。以此首次推出了B07s03TI浏y两相共存复相材料的介电常数随组成变化的理论计算公式为:In6=“、sT、52阵她习」·、1啸一e--n（ltw）+c,与实验 L几一al十戈昭r一踢￡了」结果完全一致。 （5）对复相陶瓷B07s03T0.7N住3的介电性能产生机理及过程进行了研究。揭示了钙钦矿、钨青铜复相陶瓷B07503T0.召仓3的形成反应机理及形成过程。发现了钙钦矿相含量增加及晶粒尺寸增大,束缚了钨青铜相的铁电/)l项电相变,钨青铜相居里点升高;反之,钨青铜相晶粒尺寸增大,阻碍钙钦矿相晶粒生长,束缚作用减弱,居里点略微降浙江大学博士学位论文摘要低。发现了体系内两相共存在晶界易引入缺陷,促使在电场作用下产生较多的极化子,低更多还原

【Abstract】 The performance of IR imagers is dependent on the pyroelectric materials used in the uncooled focal plane arrays (UFPAs). As we known, the strongest responsivity of the pyroelectric materials is generated near the Curie point; so, the imagers request a curious operating temperature in order to obtain the strongest responsivity. Furthermore, a composite material having several dielectric peaks, i.e. Curie temperature points, around room temperature will possess both a stronger pyroelectric effect and a wider temperature range near the ambient through the "composite effect". Both higher performance and temperature stability of the IR imagers would be obtained without any temperature stabilizer. And it is significant for IR imaging.The aim in this paper is to prepare the composite materials with higher pyroelectric properties through the composite of Ba1-xSrxTiO3(BST) and SrxBa1-xNb2O6(SBN), and to provide the foundation for developing new IR imagers with higher performance. In the present study, the composite ceramics B0.7S0.3T1-yNy with both the perovskite and the tungsten bronze phases were successfully prepared in situ by controlling some excessivecontents of components and traditional ceramic process in 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 composite system. The relationships between the dielectric/pyroelectric properties and the microstructures of the composites B0.7S0.3T1-yNy were investigated by XRD, SEM, EDXA, impedance analyzer and the testing system for measuring pyroelectric current. Some interesting results and conclusions obtained in the work are as flows:(1) The results, about the investigation on preparation and formation of the composites B0.7S0.3T1.yNy, show that the perovskite BST (Nb) system is not stable any longer and the second phase tungsten bronze SBN appears while the excessive content of Nb2O5 is above 6 mol%, similarly, the tungsten bronze SBN(Ti) system is not stable any longer either and the second phase perovskite BST appears while the excessive content of (BaO+SrO) is above 11mol%. In the composite ceramics B0.7S0.3T1-yNy in which the SBN phase and BST phase coexist, the tungsten bronze phase exists in the state of SBN (Ti) solid solution while the perovskite phase almost exists in the state of pure BST or BST (Nb) solid solution doped only with little Nb2O5.(2) The dielectric properties of the composite ceramics B0.7S0.3T1-yNy have both characteristics of the perovskite phase and the tungsten bronze phase. The r and tan of theB0.7S0.3T1.yNy depend on the relative content of the perovskite phase as well as the solubility of Nb5+ ions in it. The phase transition temperature of the tungsten bronze phase depends on the solubility of Ti4+ ions in the phase and the relative content of the perovskite phase. The lowest transition temperature is around 200°C and it is about 90°C lower than the pure tungsten bronze phase SBN.(3) The microstructure of the composite ceramics B0.7S0.3T1.yNy consisted of two kinds of grains. The smaller polygonal grains belonged to the BST phase, and the larger ones to the SBN phase. The coexistence of the two phases inhibited the growth of the BST crystal. The density of microstructure of the composite ceramic was higher than that of both the pure BST and SBN sintered at same temperature and for same time, due to the void among the larger SBN grains were filled with the smaller BST grains.(4) A new formula is firstlyput forward to calculate the dielectric constant of a composite material with two phases prepared in situ, according to the experimental results about the composite ceramics B0.7S0.3T1-yNy and considering the effects of solid solution between the two phases.(5) The formation mechanism of the composite ceramics B0.7S0.3T1-yNy is investigated. The results revealed that the phase transition of the tungsten bronze phase increased as the content or the grain size of the perovskite phase increased and decreased as the grain size of the tungsten bronze phase increased. The defects between the grain boundaries of different phase increased when the tw更多还原