摘要
铁电压电材料因其优异的性能在军事、医学、通讯等领域中得到了广泛的应用。目前使用的铁电压电材料主要以传统的锆钛酸铅陶瓷为主,但它的含铅重量达到60%以上。近年来,铅由于其毒性已经被很多材料研究及商业应用排除在外,更多的关注投向了无铅压电材料。
在众多的无铅材料中,铌酸钾钠(简称KNN)表现出较高的铁电压电性能。目前,KNN基铁电压电材料的研究主要集中于陶瓷材料,而对于KNN基铁电压电单晶的研究报道很少。铁电单晶的结构比陶瓷简单,便于进行随晶体取向变化物理机理的研究;更为重要的是,铁电单晶的介电、压电、机电耦合、铁电等性能都远远超出同组分的陶瓷材料,因此对无铅铁电单晶的研究具有学术和应用的双重意义。因此,本文以钽铌酸钾锂晶体作为研究对象开展系统研究。在本文中,我们先进行了钽铌酸钾锂晶体的生长和样品制备,然后对它的介电温谱、压电参数和电滞回线等进行了研究:
(1)采用顶部籽晶法生长了钽铌酸钾锂晶体,然后经过定向、切割、研磨、镀制电极以及单畴化处理进行了压电振子的制备;
(2)对钽铌酸钾锂晶体的介电温谱进行了测定,得到其居里温度和四方正交铁电相变温度,并对驰豫特性进行了定性分析和定量的分析,得到了钽铌酸钾锂晶体的驰豫因子及变化规律;
(3)对钽铌酸钾锂晶体的横向长度伸缩振动模式压电参数进行了理论推导和实验测试,得到横向长度伸缩振动模式、厚度振动模式的压电常数和机电耦合系数;对钽铌酸钾锂晶体的电滞回线进行了测定,得到矫顽场、剩余极化强度以及最大极化强度,并对结果与其他无铅铁电压电材料的相关数据进行了对比和分析。各项性能指标都优于已有的材料,所以钽铌酸钾锂晶体是一种性能优良的无铅铁电压电材料。
鉴于优越的压电、铁电性能,钽铌酸钾锂晶体可在如超声换能器、压电驱动器等器件方面得到很好的应用。
Ferroelectric and piezoelectric materials have wide application to the fields of military, medicine and communications for their excellent properties. At present, most of ferroelectric and piezoelectric materials are lead zirconate titanate ceramics, but they contain more than 60 weight percent lead. Recently, lead has been expelled from many materials researches and commercial applications regarding its toxicity. Increasing attention has been paid to the lead-free piezoelectric materials.
Potassium Sodium niobate (abbreviated as KNN) was of superior ferroelectric and piezoelectric properties among numerous lead-free materials. Nowadays, the studies of KNN-based ferroelectric and piezoelectric materials were mostly focused on ceramincs, and few reports on the KNN-based single crystals. Single crystal provides the opportunity to conveniently investigate the physical properties as a function of crystallographic orientations; more importantly, it always has the better dielectric, piezoelectric and ferroelectric properties than that of the same composition ceramic. So, there is not only academic meaning but also application value for study of lead-free ferroelectric single crystal.
So, in this work, we carried out systematic research for tantalum potassium lithium niobate (shorted as KLTN) crystals. In this work, we firstly grown KLTN crystals and prepared the samples, then researched their dielectric constants dependence with temperature, piezoelectric parameters and hysteresis loops (P-E loops):
(1) The crystals used in this work were grown by the top-seeded solution growth method, and then we prepared the piezoelectric vibrators, including orienting, cutting, grinding, electrode coating and single-domain processing;
(2) We measured dielectric constants dependence with temperature of KLTN crystals to obtain their curie transition temperatures and tetragonal- orthorhombic ferroelectric phase transition temperature, and discussed the relaxation characteristics qualitatively and quantitatively to obtain the relaxation factors and its changing law;
(3) We derived and measured piezoelectric parameters, including piezoelectric constants and electromechanical coupling coefficients of length extension vibration mode and thickness mode. And we obtained coercive field, remnant polarization and maximum polarization through measuring hysteresis loops of KLTN crystals, and comparing the data with other lead-free ferroelectric and piezoelectric materials. The properties were better than existing ceramics, so KLTN crystals were excellent piezoelectric and ferroelectric materials.
Because of the excellent piezoelectric and ferroelectric properties, KLTN crystals are very promising lead-free piezoelectric materials for a wide range of applications, such as ultrasonic transducer, piezoelectric actuator, etc.
引文
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