【作者】 陈旻；

【导师】 徐庆；

【作者基本信息】 武汉理工大学 ， 材料学， 2006， 硕士

【摘要】 钛酸铋钠((Na_0.5Bi_0.5))TiO₃,简称NBT)是一种A位复合钙钛矿结构铁电体,其居里温度T_c为320℃,在室温下具有很强的铁电性（P_r=38μC/cm²）,是当前无铅压电陶瓷很有希望的候选材料之一。本论文采用柠檬酸盐法制备了(Na_0.5Bi_0.5)_1-xBa_xTiO₃（简称NBT-（x）BT）体系无铅压电陶瓷,系统研究了镧系稀土氧化物添加剂对组成在准同型相界（MPB）附近的NBT-（x）BT陶瓷的结构与电学性能的影响及其规律,并结合实验结果探讨了该体系陶瓷的介电弛豫特性、相变特性以及材料的铁电性质对乐电性能的影响与作用。 采用柠檬酸盐法合成与制备了NBT-（x）BT体系陶瓷,对NBT-（x）BT陶瓷的结构和电学性能进行了系统的研究。发现与常规固相法相比,采用柠檬酸盐法可以显著提高NBT-（x）BT体系陶瓷的铁电性能、压电性能及其稳定性。由晶体结构研究确定了NBT-（x）BT体系陶瓷的MPB处于x=0.06～0.10的范围内,并发现三方和四方相的相对含量对MPB附近的NBT-（x）BT组成的压电性能具有很大影响,当相组成处于MPB附近略偏四方一侧时（x=0.07）,陶瓷样品的综合压电性能达到最佳。 研究了La₂O₃和CeO₂对(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃体系陶瓷结构与电学性能的影响。研究结果表明,添加La₂O₃和CeO₂对材料的显微结构未产生显著影响,对陶瓷样品的晶体结构影响较大,随着La₂O₃和CeO₂添加量的增加,陶瓷样品中四方相的相对含量逐渐增多。当La₂O₃的添加量较低时（≤0.2wt%）,陶瓷样品的压电常数d₃₃随La₂O₃添加量的增加而有所提高,但添加La₂O₃也使得陶瓷样品的机电品质因子Q_m降低、介电损耗tgδ增加,此时La₂O₃表现出软性添加物的特征。当CeO₂的添加量较低时（≤0.2wt%）,随着CeO₂含量的增加,陶瓷样品的压电常数d₃₃略有减小,机电耦合系数k_p有所增加,介电损耗tgδ趋于减小,机械品质因子Q_m呈现增加的趋势,这表明CeO₂对陶瓷样品电学性能的影响具有“软”、“硬”双性掺杂的特点,这可能是由于Ce电子结构的特点（容易产生变价）所引起的。当La₂O₃和CeO₂的添加量较高时,金属离子空位数目的增多,削弱了铁电畴的稳定性,使铁电宏畴向反铁电微畴转变,从而导致陶瓷样品的去极化温度T_d降低,在室温下陶瓷样品的电滞回线出现变形,压电性能大幅度降低。 研究了(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃+0.2wt%Ln₂O₃（Ln=La、Pr、Nd、Sm、Eu、Gd）体系陶瓷的结构与电学性能。发现在镧系稀土氧化物添加量较小的条件下,陶瓷样品的压电性能主要取决于晶体结构的畸变方式和程度。随着镧系稀土离子半径的减小,陶瓷样品的压电性能呈现出逐渐降低的趋势。更多还原

【Abstract】 Recently, there is a growing interest of investigating lead-free piezoelectric materials as a possible alternative to widely used lead zirconate titanate （PZT） based ceramics. Sodium bismuth titanate, (Na_0.5Bi_0.5)TiO₃ （NBT） is considered to be one of promising candidates for lead-free piezoelectric ceramics due to a large remanent polarization （P_r=38μC/cm²） at room temperature and a high Curie temperature （T_c=320℃）. In this research, a citrate method has been employed to prepare (Na_0.5Bi_0.5)_1-xBa_xTiO₃（abbreviated as NBT-（x）BT） ceramics, and the effect of lanthanide oxide additives on the structure and electrical properties of ceramic with a composition near the rhombohedral-tetragonal morphotropic phase boundary （MPB） have been investigated. The dielectric relaxation feature and the phase transition behavior have been examined with respect to temperature and measuring frequency. The main contributing factors to the ferroelectric and piezoelectric properties of the ceramics have been established based on experimental results.NBT-（x）BT ceramics has been synthesised and prepared by the citrate method. The structural characteristics and electrical properties of NBT-（x）BT ceramics were examined. It was found that the citrate method demonstrates advantages of producing fine and homogeneous powders together with substantially improving the ferroelectric and piezoelectric properties of the resulting ceramics. The analysis of the crystal structure reveals that the MPB of the ceramics lies in the composition range of 0.06 < x <0.10 at room temperature. The piezoelectric and ferroelectric properties of NBT-（x）BT compositions near MPB are rather sensitive to the proportion of rhombohedral and tetragonal phases and reach preferred values at x=0.07, where the relative content of the tetragonal phase is a little higher than the rhombohedral phases.Effect of La₂O₃ and CeO₂ addition on the structure and electrical properties of (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ （NBT-7BT） ceramic were investigated. The crystal structure of the specimens remains the coexistence of rhombohedral and tetragonal phases. Nevertheless, with the increasing amout of La₂O₃ and CeO₂, the relative content of tetragonal phases are gradually enhanced. Compared with NBT-7BT specimen, the specimen added with a small amount of La₂O₃ shows an increase of electromechanical coupling factor （k_p） and piezoelectric constant (d₃₃), while a considerable decrease of delectric loss （tgδ） accompaned by a enhanced mechanical quality factor （Q_m） were detected for the specimens added with CeO₂. However, further increasing the amount of La₂O₃ and CeO₂ lead to a rapid degradation of piezoelectric properties and adeformation of P-E hysteresis loops, which may results from the formation of antiferroelectric micro-region in the specimens at room temperature.The structure and electrical properties of（Nao.5Bio.5）o.93Bao 07TiO3+0.2wt%Ln2O3 （Ln=La^ P^ Nd, Sitk Eu^ Gd） ceramics were examined. It was ascertained the piezoelectric properties of the specimens rely on the deformation mode and degree of the crystal structure. A degradation of the piezoelectric properties was found for the specimens with smaller lanthanide size.更多还原