【作者】 唐斌；

【导师】 田长生； 樊慧庆；

【作者基本信息】 西北工业大学 ， 材料学， 2002， 硕士

【摘要】 新型弛豫铁电单晶铌镁酸铅（简称PMNT）或铌锌酸铅（简称PZNT）是一类新兴的功能材料，其在准同型相界附近具有优于传统压电陶瓷的较高的压电常数和电致伸缩系数，可完全代替传统的压电陶瓷作为超声换能器、致动器、微位移器等，使其成为铁电领域的研究热点，但如何生长出满足应用要求的单晶材料却一直是一个困扰的问题。本论文采用高温熔液法技术，对用高温熔液法生长弛豫铁电单晶材料工艺进行了研究，成功地制备出准同型相界附近的PMNT、PZNT单晶材料，分析了晶体形成、晶体结构及其相结构稳定性，并对生长机理作了初步探索，主要研究结论如下： 1．采用高温熔液法成功地制备出钙钛矿相结构的PMNT、PZNT单晶材料，制备的PMNT、PZNT单晶颗粒大小多为0.5mm～5mm之间，晶粒呈淡黄色，少数呈灰褐色。 2．制备PMNT单晶时均生成纯立方钙钛矿相结构，无焦绿石相产生，晶体几何外形多为规则的立方结构；制备的PZNT单晶材料形状不规则，呈箭头状，且伴随有焦绿石相生成，因此纯相的PZNT单晶材料较PMNT晶体更难合成。 3．研究了高温熔液法制备PMNT、PZNT单晶的生长工艺。助熔剂和组分间的摩尔配比以6：4为佳，能够抑制焦绿石相的产生；此外，添加少量的B₂O₃作助熔剂有利于晶体的长大。 4．利用XRD和差热分析研究了弛豫铁电单晶PMNT、PZNT的相结构稳定性。在无PbO条件下PMNT晶体较PZNT晶体稳定，但在1250℃附近的高温下会发生向焦绿石相的分解反应；PZNT单晶体是亚稳定的，在高温时亦分解生成焦绿石相和PbO。 5．利用XRD技术，对PZNT单晶制备过程中的相转变进行了详细研究。提出Pb₃Nb₄O₁₃和Pb_1.83Zn_0.29Nb_1.71O_6.39两种焦绿石相结构在其生长过程中均可出现，并能转化为钙钛矿结构。其中Pb₃Nb₄O₁₃为中温段出现，Pb_1.83Zn_0.29Nb_1.71O_6.39为高温段出现。 6．用SEM初步观察到PMNT单晶微米量级的宏畴结构。 7．分析了弛豫铁电单晶的晶体缺陷，并根据晶体形貌相提出弛豫铁电单晶PMNT、PZNT的生长机制符合PBC理论模型，属典型的二维层状生长，其包络面为{100}面，生长最快的方向为[111]晶向。 8．自行设计和组装的中温电阻炉温度自动控制系统满足设计要求，运行效果良好。更多还原

【Abstract】 Relaxor ferroelectric single crystals , such as Pb(Mg1/3Nb2/3)-PbTiO3 (abbreviated as PMNT) or Pb(Zn1/3Nb2/3)-PbTiO3 (abbreviated as PZNT), have been reported to exhibit an extremely large piezoelectric constant and excellent electrostrictive properties. Such excellent performance makes it fully substitute the traditional piezoelectric ceramics and points to a revolution in ultrasonic transducers, actuators and micro-positioners, making relaxor-based piezocrystals the most promising materials for a broad range of advanced applications. However, it is difficult to grow the high quality single crystals because of the lack of valid thermodynamic data.In this paper, PMNT, PZNT single crystals in the vicinity of the morphotropic phase boundary were obtained by high-temperature solution technique. The growth, structure and phase stability of single crystals were studied. The results are shown as follows:1. By high-temperature solution technique, the PMNT, PZNT single crystals with perovskite structure were successfully prepared and the crystals showed size from 0.5mm to 5mm, and color from light yellow to brown.2. As-grown PMNT single crystal were pure perovskite structure and regular pseudo-cubic while PZNT showed an arrow-head shape with the formation of pyrochlore phases.3. Processing conditions were optimized in order to increase the size and yield of perovskite crystals by a high temperature flux solution method. The optimum mole ratio of flux to composition was found to be 6:4, which can restrain the formation of pyrochlore phase. It was revealed that B2O3 additive played an important role in increasing the size of single crystals.4. Phase structure stability of PMNT, PZNT single crystals were systematically studied by X-ray diffraction (XRD) method and differential scanning calorimetry (DSC). Under no excess PbO flux environment, the perovskite phase of PMNT single crystals were more stable than that of PZNT, but it was found to be the decomposition of perovskite crystals into pyrochlore crystals at 1250℃. The pure perovskite PZNT crystals prepared by the PbO flux method were thermodynamically metastable. yielding pyrochlore and PbO over high temperature.5. The formation mechanism of the ferroelectric perovskite in PZNT was examined by X-ray diffraction method. Both of pyrochlore phases of Pb3Nb4O13 and Pb1.83Zn0.29Nb1.71O6.39 were obtained during the growth of single crystals, butPb3Nb4O13 existed during middle temperature period while Pb existed during high temperature peroid.6. Domain configuration in PMNT single crystals were observed using scanning electronic microscope (SEM).7. The defects existing in piezoelectric single crystals were analyzed. It is shown that the morphology of PMNT, PZNT crystals was related to a layer growth mechanism controlled by two-dimensional nucleation which can be depicted by the theoretical model of periodic bond chains (PBC).8. The temperature autocontrol system of middle-temperature resistance furnace was designed and assembled, which meet experimental requirements.更多还原