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SBN基陶瓷的制备及性能的研究
【作者】 谷睿；
【导师】 杨祖培；
【作者基本信息】 陕西师范大学 ， 无机化学， 2010， 硕士
【摘要】 随着人类环保意识的增强及社会和和生态环境可持续发展的需要,无铅压电陶瓷材料的开发及其应用研究已经成为了各国学者竞相关注的热点。然而,无铅压电陶瓷材料的性能与传统含铅压电陶瓷相比还有一定的差距。所以开发高性能的无铅压电陶瓷体系成为了一项迫切需要研究的课题。铌酸锶钡(Sr, Ba) Nb2O6具有优异的电光、压电、热点和光折射性能,是无铅铁电领域最具研究潜力的材料之一。但铌酸锶钡陶瓷存在着烧结温度高、压电和介电性能相对较低等缺点,并且较难制备出具备良好致密性和较优性能的样品。本文采用传统固相法制备了SrxBa1-xNb2O6(简称SBN)基无铅压电陶瓷,并且从配方设计、烧结工艺及掺杂改性三方面进行了研究。研究了组分变化对体系相结构、微观形貌、密度以及介电和铁电性能的影响,并且筛选出较优组分(Sr0.53Ba0.47Nb2O6)。在此基础上,选择了Na+、Ta5+和LiSbO3作为取代和掺杂剂,对较优组分体系进行了A、B和C位的取代和掺杂研究,以期达到降低烧结温度、降低介电损耗、提高陶瓷致密度和优化电性能的目的。主要内容如下：首先,系统地研究了Sr/Ba比的变化对SBN陶瓷的相结构、显微结构以及电性能的影响。结果表明：原料粉体在1200℃下预烧4h时,当x<0.51,可得到四方钨青铜结构单相,而当x>0.51时,XRD图谱中出现了SrNb2O6的峰,即随着Sr/Ba的增大,粉体的预烧变得困难。而在1250℃下预烧4h时,所有组分的陶瓷粉体均为四方钨青铜结构,即对于同一组分的原料粉体,提高预烧温度,容易得到纯相。所有组分在1380℃/6h的条件下均可获得致密性良好的陶瓷,没有出现明显的晶粒异常长大现象。在x=0.53时,陶瓷密度达到理论密度的92%。各组分陶瓷样品在室温下的介电常数随Sr/Ba的增大而增大,且居里温度Tc随Sr/Ba增大从86℃降低到65℃。所有组分的陶瓷样品均为典型的弛豫铁电体。它们都具有饱和的电滞回线,随着Sr/Ba比的增加,陶瓷样品的剩余极化强度Pr和矫顽场Ec都变化不大。综合各方面性能,得出具有较优性能的组分为x=0.53：此时性能为：Tc=77℃,εm=2774, Pr= 1.09μC/cm2,Ec=3.66 kV/cm。其次,选用Na+、Ta5+作为取代离子,对已经筛选出的最佳组分Sr0.53Ba0.47Nb2O6的晶体结构中的A、B位进行取代研究,以期提高陶瓷样品的致密度,降低介电损耗,进一步改善陶瓷的电性能。结果表明：(1)当Na+单独取代A位时, Na+的含量在0.1-0.8mol的范围内,所有陶瓷样品均属于四方钨青铜结构。随着Na+含量增加,陶瓷晶粒尺寸增大,陶瓷样品的弛豫性特征消失,温度频率稳定性增加,居里温度大幅度提高,且铁电性增强。居里温度Tc从77℃增大到310℃C,当Na+含量为0.6时,综合性能较优,分别为：Tc=310℃,εm=2021,Pr=2.07μC/cm2, Ec=6.46kV/cm。(2)当Ta5+单独取代B位时：Ta5+含量在0.05-0.40范围内,所有陶瓷样品均为四方钨青铜结构,晶格参数的改变使所有组分的衍射峰都稍稍向低角度方向偏移。随着Ta5+含量增大,陶瓷样品的致密性提高,密度最大可达到理论密度的98.3%,介电损耗大幅度降低(最低可达到4.9×10-4),居里温度降低,弛豫性增强,铁电性减弱。当Ta5+含量为0.1时,其综合和性能较优,分别为：Tc=25℃,εm=2387,tanδ=0.027。(3)当Na+和Ta5+同时取代A、B位时,Ta5+取代量固定为0.1。当Na+含量在0.3-1.05的范围内,所有陶瓷样品均属于四方钨青铜结构。当Na+含量大于0.7时,陶瓷样品的温度介电谱图上在130℃附近出现了一个介电单峰,形成了“介电双峰”效果,并随着Na+含量的增大而愈加明显。随着Na+含量从0.3变化到1.05,陶瓷样品的温度频率稳定性升高,但弛豫特性减弱。综合各方面性能考虑得出具有较优性能的组分为当Ta5+含量为0.1,Na+含量为0.6时,综合性能为：Tc=248℃,εm=2472, Pr= 2.07μC/cm2,Ec=7.25 kV/cm.最后,在筛选出的最佳组分Sr0.53Ba0.47Nb2O6的基础上引入LiSbO3,研究了LiSbO3含量的变化对陶瓷相结构、微观形貌以及电性能的影响,以期降低烧结温度,并且改善其电性能。结果表明：LiSbO3的含量在0.01-0.04mol的范围内,所有陶瓷样品均属于四方钨青铜结构。随着LiSbO3含量增加,陶瓷晶粒尺寸减小,形貌更为均匀致密,居里温度降低(79℃降低到32℃),晶格参数变化,铁电性减弱。适量地引入LiSbO3可以明显的降低陶瓷粉体的预烧温度和陶瓷体的烧结温度,预烧温度从1250℃降低到1180℃,烧结温度从1400℃降低到1280℃。所有组分陶瓷样品为典型的弛豫型铁电体。在1280℃下烧结6h且LiSbO3的含量为0.03时,其综合性能较优,分别为：Tc=44℃,εm=2392, Pr=0.59μC/cm2,Ec=2.36kV/cm。
【Abstract】 As every country in the world pays more and more attention to environmental protection, the research of lead-free piezoelectric ceramics becomes very important. Compared with traditional lead-based piezoelectric ceramics, there are many drawbacks of lead-free piezoelectric ceramics. So, it is practical and realistcic to find a lead-free piezoelectric system with optimum properties. Due to the properties of SrxBa1-xNb2O6 (abbreviated to SBN), such as pyroelectric and linear electro-optic coefficients. SBN is considered to be one of the most promising lead-free ceramics to substitute lead based ceramics.We adopted conventional oxide-mixed method to prepare SBN-based lead-free piezoelectric ceramics. The effects of composition, sintering technique and doping element were also investigated. The major content was as follows:Firstly, the effects of Sr/Ba ratio and sintering technique on phase structure, microstructure and electrical properties were studied detailedly. The results showed that all samples exhibited single tungsten bronze (TB) structure. Prepared powder calcined at 1200℃/4h, when x<0.51, it exhibited single-phase tungsten bronze structure, and when x> 0.51, XRD patterns emerged SrNb2O6 peak, that is, as Sr/Ba increases, the powder calcined become difficult. When calcined at 1250℃for 4h, all samples exhibited single-phase of tetragonal tungsten bronze structure, that is, the prepread powder for the same components, increase calcined temperature, easy to obtain single-phase. The ceramics sintered at 1380℃with relatively compact and homogenous microstructure without abnormal grain growth can be obtained at x=0.53. Dielectric constant increased and Tc decreased from 86℃to 65℃with increasing the Sr/Ba ratio, and at the same time the ceramics presented better properties, which were as follows:SBN53 has the clear grain boundary and uniform grain size, its density reaches the highest value of 4.934 (92% of theoretical density). Tc=77℃,εm=2774, Pr= 1.09μC/cm2, Ec=3.66 kV/cm。The material belongs to an ideal relaxor ferroelectric.In order to decrease dielectric loss of the ceramics and improve the electrical properties, further, we choose Na+and Ta5+ as dopants. Only Na+ as dopant, all ceramics exhibited single tungsten bronze (TB) structure as Na+ content ranged from 0.1 to 0.8 mol. The SEM images indicated that with Na+ content increasing, the average grain size increased, and the compact and uniform ceramics can be obtained at Na+= 0.6 mol. With Na+ increasing, relaxor behavior disappeared, temperature frequency stability increased and the Curie temperature Tc increases from 77℃to 310℃. When Na+= 0.6 mol, the electrical properties of the ceramics sintered at 1380℃were better, which were as follows:Tc=310℃,εm=2021, Pr= 2.07μC/cm2,Ec=6.46 kV/cm. Only Ta5+ as dopant. As Ta content range from 0.05 to 0.40, all samples exhibited single tungsten bronze (TB) structure, all the diffraction peaks of Sr0.53Ba0.47Nb2-xTaxO6 slowly shift to the left. With Ta5+ increasing, the average grain size decreased, and the compact and uniform ceramics can be obtained at Ta5+=0.2mol. Tc decrease from 75℃to-57℃as Ta5+ increase from 0.05 to 0.4, while the maximum dielectric constant reduced from 2723 small to 1294. When Ta5+=0.1 mol, the electrical properties of the ceramics sintered at 1430℃were better, which were as follows:Tc=25℃,εm=2387, Pr=0.24μC/cm2,Ec=1.76kV/cm.Na+, Ta5+ doped together, Ta5+ content is 0.1mol, when Na+content in the range of 0.3 to 1.05, all samples exhibited single tetragonal tungsten bronze structure. When the content of Na+>0.7, the sample exhibit a peak of phase transition at 130℃. With Na+ increasing, the temperature frequency stability increased, but relaxor behavior disappeared. When Ta5+=0.1mol and Na+= 0.6mol, the electrical properties of the ceramics sintered at 1400℃were better, which were as follows:Tc=248℃,εm=2472, Pr=2.07μC/cm2,Ec=7.25 kV/cm.Although doped Ta5+ can increase the density of the ceramic decrease dielectric loss, Na+doped can increase the Tc. But the sintering temperature of SBN ceramics is too high. So finally we choosed LiSbO3 as dopant. We studied the effects of LiSbO3 content on phase structure, microstructure and electrical properties in order to improve the dielectric properties of the ceramics and decrease the sintering temperature. The results show that:The X-ray diffraction patterns indicated that all samples exhibited single tungsten bronze (TB) structure as LiSbO3 content ranged from 0.01 to 0.04. The addition of LiSbO3 promote densification of ceramics. The SEM micrographs showed that with LiSbO3 content increasing, the average grain size decreased and the relatively compact and uniform ceramics can be obtained at x=0.03. The addition of LiSbO3can decrease the sinter temperature from 1380℃to 1280℃. The temperature dependence of dielectric constant and dielectric loss revealed that all ceramics were relaxor ferroelectrics. When LiSbO3=0.02 mol, the electrical properties of the ceramics sintered at 1280℃were better, which were as follows:Tc=44℃,Pr=0.59μC/cm2,Ec=2.36 kV/cm.