摘要
锆钛酸铅(PZT)基压电陶瓷由于其优异的压电性能在生产和生活中有着广泛的应用。但是这类材料含有大量Pb元素,使得该类材料的应用受到极大的限制,因此,开发新型高性能无铅压电陶瓷意义重大。碱金属铌钽酸基压电材料由于具有无毒和高压电性能等优点,受到各国学者的重视。本文详细的研究了熔盐法制备Na_(0.5)K_(0.5)NbxTa(1-x)O3 (x=0.3~0.7)系压电陶瓷的工艺条件,寻找出性能最佳的组分,并探讨了A位(稀土元素,碱金属)和B位(过渡金属)掺杂对材料压介电性能的影响,发现经过掺杂改性的陶瓷材料的部分电性能可以和PZT相媲美。
本文系统地研究了熔盐法合成Na_(0.5)K_(0.5)NbxTa(1-x)O3 (x=0.3~0.7)及其掺杂样品的工艺条件,研究发现反应原料在850℃,保温4小时,熔盐(NaCl-KCl)与原料质量比为1:1时,可获得单相的Na_(0.5)K_(0.5)NbxTa(1-x)O3 (x=0.3~0.7)及其掺杂样品。在此基础上研究了粉体样品的相组成,颗粒的微观形貌和陶瓷材料的压介电性能。研究结果表明:烧结条件为1100℃烧结,保温40分钟,极化条件为在120℃油浴中加热20分钟,极化场强为4kv/mm时,陶瓷样品的压介电性能最佳。
对Na_(0.5)K_(0.5)NbxTa(1-x)O3 (x=0.3~0.7)以及A位(稀土元素,碱金属)和B位(过渡金属)掺杂样品的压介电性能测试结果表明:当Nb和Ta原子比为1:1时,材料具有最佳压介电性能,材料的几个重要性能参数分别为:εr=83.2,tanδ=0.0096,d33=152pc/N,TC=700℃。在此基础上研究了A位和B位掺杂对陶瓷材料压介电性能的影响,当CuO的掺杂量为1.0mol%时,陶瓷具有较好的压介电性能:εr=220,tanδ=0.01, d33=170pc/N;对于稀土离子(La3+、Nd3+、Sm3+)掺杂体系,当Sm3+的含量为2.0mol%时,性能较佳:εr=133.4,d33=158pc/N。Li+的掺杂样品中当Li+含量为8.0mol%时,εr达到260.1。并进一步研究A,B位同时掺杂对材料压介电性能的影响,发现Sm3+和Cu2+掺杂量分别为2.0mol%和1.0mol%时,陶瓷样品性能参数为εr=345.6 ,tanδ=0.011,d33=254pc/N,Tc=690℃,可以看出该陶瓷样品的部分电性能已接近固溶体Pb(Zr,Ti)O3(PZT)基压电材料的性能。
最后,本文简单介绍了压电陶瓷材料介质极化的类型,结合测试数据讨论了频率和温度对介电性能的影响,并运用Clausius-Mosotti方程结合离子极化率计算了介电常数。结果表明:当测试频率小于40000Hz时,介电常数及介电损耗均随频率的增加而减小。介电常数的计算值与实测值有较大的偏差,导致这一结果的可能原因是计算时未考虑内电场的作用。
Although Pb(Zr, Ti)O3 (PZT)-based piezoelectric ceramics have excellent piezoelectric performance, their applications are limited to some extent, due to the high content of Pb. So the exploitation of high performance lead-free piezoelectric ceramics have great sense. In the field of lead-free piezoelectric ceramics, alkali metal niobate and tantalum-based materials have large potentials to become the next generation piezoelectric ceramics because of their no toxicity and high performance.
In the current study, sodium potassium niobate-based piezoelelctric ceramics were successfully prepared by molten solten meothod, and then the preparation conditions such as synthesis temperature, systhesis time and the ratio of assistant molten agent against the starting materials were systematically studied. Rare earth, alkali and transition metal element were used to enhance the piezoelectric performance of the ceramics. It has been found that a series of the composition Na_(0.5)K_(0.5)NbxTa (1-x) O3 (x=0.3~0.7) and their doped ceramics can be obtained after prosessing at 850℃for 4 hours. To study the piezoelectric properties of the samples, the ceramics were processed according to the route: being sintered at 1100℃in air for 40 minutes, being handled in silicon oil at 120℃for 20 minutes, being polarized in the electric field 4kv/mm.
In this paper, the piezoelectric and dielectric properties of the composition Na_(0.5)K_(0.5)NbxTa (1-x) O3 (x=0.3~0.7) and their doped ceramics were investigated. The measurement of piezoelectric and dielectric propterties reveals that two propterties are better when the atom ratio of Nb against Ta is 1:1 andεr, tanδ, d33 and TC are 83.2, 0.0096, 152pC/N and 700℃, respectively; for rare earth doped samples, the substitution of Sm3+ element has more marked effect on the enhancement of poizoelectric and dielectric performance ,εr and d33 for Sm 2.0mol% sample are 133.4 and 158pC/N, respectively; for Cu2+ 1.0mol% doped sample, two properties are better andεr, tanδand d33 are 220, 0.011, 170pC/N respectively. When Li+ doped amout is 8.0mol%,εr can reach 260.1. With consideration of improvement of two properties, the substitution of A postion element together with B were done, it is found that when the Sm3+ and Cu2+ contentare 2.0mol% and 1.0mol%,εr ,tanδ, d33and Tc are345.6, 0.011, 254pC/N and 690℃, respectively ,which can be comparable to PZT.
At last, we simply introduce the type of polarization of piezoelectric ceramics. By combination of experiment results, the effects of frequency and temperature on diezoelectric performance are discussed and then dielectric constants are theoretically calculated by Clausius-Mosotti equation with polarization of ions. The results show that when the frequency is below 40000Hz,εr and tanδdecreasd with increasing frequency. The calculated values deviated from experimental values larger; the possible reason is that we can not consider the effect of inner electric field in the calculation process.
引文
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