【作者】 盖志刚；

【导师】 王矜奉；

【作者基本信息】 山东大学 ， 材料物理与化学， 2008， 博士

【摘要】 压电材料是能在外加机械力的作用下产生极化并形成表面电荷，或在外加电场作用下产生形变的功能材料。通过外力产生电荷的现象，称为正压电效应，是由居里兄弟于1880年发现的。压电效应是一种机电耦合效应，将机械能转换为电能，称为正压电效应。反之，压电晶体置于外电场中，由于外电场的作用引起晶体内部正负电荷中心的位移-极化位移而导致晶体发生形变，称为逆压电效应。这两种效应统称为压电效应。铋层状结构化合物由于其独特的结构特性和高居里温度引起了人们的重视。铋层状结构压电材料在滤波器、能量转换、高温高频领域具有广泛的应用前景。铋层状结构化合物是由二维的钙钛矿层和含铋的（Bi₂O₂）²⁺层沿c轴有规则的相瓦交替排列而成。本文研究了（1-y）[(Na_0．96-xK_xLi_0．04)_0．5Bi_0．5]TiO₃-yBa(Zr_0．055Ti_0．945)O₃无铅压电陶瓷的压电介电特性，得到了压电系数d₃₃高达185（pC／N）的无铅压电陶瓷0．94[(Na_0．80K_0．16Li_0．04)_0．5Bi_0．5]TiO₃-0．06Ba(Zr_0．055Ti_0．945)O₃。在对铋层结构陶瓷结构和极化过程改性上，A位或（和）B位替代被证明是有效的。而且已经证实，Ce掺杂可以有效的提高铋层结构陶瓷的电阻率和压电活性。本文研究了Ce掺杂Bi₃TiNbO₉系列超高温铋层结构无铅压电陶瓷，还研究了（LiCe）复合替代[（Na,K）_0．5Bi_4．5Ti₄O₁₅]系列、[（Na,K）_0．5Bi_2.5Nb₂O₉]系列高温铋层无铅压电陶瓷。本文分析了铋层结构压电陶瓷压电活性低的原因，探索出提高其压电活性和性能的方法。对（Li,Ce）的A位替代对A位含缺位的（Na，K）_0．5Bi_2．5Nb₂O₉系列陶瓷的影响进行了研究，使该系列陶瓷的压电活性获得了大幅度的提高。该（Na，K）_0．5Bi_2．5Nb₂O₉系列陶瓷的压电系数d₃₃达到了28 pC／N，比报道的高温铋层陶瓷的d₃₃值（～5-19pC／N）高出了50％。用传统固相烧结法方法制备了A位缺位的（Na，K）_0．5Bi_4.5Ti₄O₁₅系列陶瓷。（Li,Ce）掺杂极大的提高了（Na，K）_0．5Bi_4．5Ti₄O₁₅系列陶瓷的压电活性和介电系数。该（Na，K）_0．5Bi_4．5Ti₄O₁₅系列陶瓷的压电系数d₃₃达到了26 pC／N，该值达到了纯Na_0．5Bi_4．5Ti₄O₁₅陶瓷压电系数d₃₃值（～10pC／N）的2．5倍以上。在ScTa复合替代BTNO陶瓷中，Bi₃Ti_0．96Sc_0．02Ta_0．02NbO₉超高温陶瓷具有非常高的压电系数d₃₃值（12 pC／N）和超高居里温度T_C（905℃）。这一成果突破了前人T_C能达到900℃但压电活性却很低(d₃₃值为6 pC／N)的记录。为了提高其电阻率、进一步提高其压电活性，用CeO₂对ScTa替代的BTNO进行掺杂，系统研究了CeO₂对该陶瓷压电活性和电阻率的影响。Bi₃Ti_0．96Sc_0．02Ta_0．02NbO₉+xwt．％CeO₂（x=0．35）陶瓷的d₃₃提高到18 pC／N，该值是前人未改性的Bi₃TiNbO₉压电性能（6pC／N）的3倍。压电振子低频振动模式的高次泛音易与厚度振动模式的基频相耦合，导致厚度振动的基音串联谐振频率不能精确测量（或无法测量），造成传统泛音比法测定压电振子的机电耦合系数的精度和一致性变差或无法进行测定。为了克服传统泛音比法的这一弊端，本文提出了测定压电振子厚度振动机电耦合系数的高次泛音比法。此法通过测定3次和3次以上的高次串联谐振频率，用高次泛音比来测定压电振子厚度振动机电耦合系数。实验表明，与传统泛音比法相比，高次泛音比法具有精确度高和一致性好的明显优势。为了便于高次泛音比法的应用，提供了高次泛音比和机电耦合系数的对应表。更多还原

【Abstract】 Piezoelectric materials are such a functional materials which can be polarized to generate the surface electric charge by exerting a mechanical stress on them, or can be deformed by exerting an electric field on them. The phenomenon of generating electrical charge by applying a stress on an object is called direct piezoelectric effect, which was first discovered by the brothers Curie in 1880. The piezoelectric effect is an electromechanical coupling effect, the direct piezoelectric effect transforms mechanical energy into electric energy. Otherwise, the converse piezoelectric effect describes the strain developed in a piezoelectric material due to the displacement of the positive and negative electric charge center （the polarization displacement） when an electric field is applied. The direct piezoelectric effect and the converse piezoelectric effect are both called the piezoelectric effect.The Aurivillius phase BLSF materials, possessing unique structure characteristic and high Curie temperature, have been given more attention. The bismuth layer-structured piezoelectrics have been widely used in filter, energy transform , high temperature and high frequency situations. The Aurivillius phase bismuth layer-structured compounds are comprised of planar pseudo-perovskite layers interleaved with （Bi₂O₂）²⁺ layers along the c axis of the BLSFs.In this thesis, （1-y）[(Na_0.80K_0.16Li_0.04)_0.5Bi_0.5]TiO₃-yBa(Zr_0.055Ti_0.945)O₃ lead-free piezoelectric ceramics were syetematically investigated. The 0.94 [(Na_0.80K_0.16Li_0.04)_0.5Bi_0.5]TiO₃-0.06Ba(Zr_0.055Ti_0.945)O₃ ceramics having a piezoelectric strain constant d₃₃ as high as 185（pC/N） was obtained.The A-site substitution or/and B-site substitution have been shown to be effective approaches in modifying the structure and polarization process of the BLSF ceramics, and it has been demonstrated that doping Ce into the BLSF is an effective way to increase their resistivity and improve their piezoactivity. In this thesis, the Ce doped ultrahigh Curie temperature bismuth layer-structured ferroelectrics bismuth titanate niobate （Bi₃TiNbO₉） compound is investigated, the （LiCe） co-substituted sodium potassium bismuth titanate [（N,K）_0.5Bi_4.5Ti₄O₁₅] and sodium potassium bismuth niobate [（Na,K）_0.5Bi_2.5Nb₂O₉] materials are investigated. We analyzed the origin of low piezoelectric activity of the reported BLSFs, and put forward a new idea to improve the piezoelectric activity for bismuth layer-structured compound.The effect of （Li,Ce） substitution for A-site on the properties of （Na,K）_0.5Bi_2.5Nb₂O₉-based ceramics with A-site vacancy was investigated. The piezoelectric activity of （Na,K）_0.5Bi_2.5Nb₂O₉-based ceramics is significantly improved by the modification of lithium and cerium. The piezoelectric coefficient d₃₃ of the （Na,K）_0.5Bi_2.5Nb₂O₉-based ceramic was found to be 28 pC/N, 50% higher than the reported d₃₃ values of other BLSF systems （-5-19pC/N）.（Na,K）_0.5Bi_4.5Ti₄O₁₅-based materials with A-site vacancy were synthesized using conventional solid state processing. The （Li,Ce） modification of （Na, K）_0.5Bi_4.5Ti₄O₁₅-based materials resulted in the obvious improvement of the piezoelectric activity and dielectric permittivity. The piezoelectric coefficient d₃₃ of the （Na,K）_0.5Bi_4.5Ti₄O₁₅-based ceramic was found to be 26 pC/N, more than 2.5 times as large as the d₃₃ value of the pure Na_0.5Bi_4.5Ti₄O₁₅ ceramics （-10pC/N）.Among the ScTa co-substituted BTNO, fabricated Bi₃Ti_0.96Sc_0.02Ta_0.02NbO₉ ceramics has a quite high piezoelectric constant d₃₃ of 12 pC/N and an ultrahigh T_C of 905℃.The result has broken the former record that the T_C can reach to 900℃but the piezoactivity is quite low( d₃₃-6 pC/N ).To increase the resistivity and further improve the piezoactivity of ScTa co-substituted BTNO, the effects doping CeO₂ into ScTa co-substituted BTNO on its resistivity and piezoactivity were systematically investigated. The d-（33） of Bi₃Ti_0.96Sc_0.02Ta_0.02NbO₉+xwt.%CeO₂（x=0.35） was found to be 18 pC/N, which is the highest value among the Bi₃TiNbO₉-based ceramics, and 3 times as large as the d₃₃ values of the former not modified BTNO ceramics （-6pC/N）.The thickness fundamental resonance is liable to coupling with the higher overtone of low-frequency-resonant modes, which leads to a bad measurement accuracy of the thickness series resonance fundamental frequencies or a failure of the resonance fundamental frequency measurement, resulting in deteriorating the accuracy and the identity of the electromechanical coupling factor determined by the traditional overtone ratio method. To overcome the shortcoming of the traditional overtone ratio method, a higher overtone ratio method to determine the thickness vibration electromechanical coupling factors was advanced in the paper. The higher overtone ratio method determines the thickness vibration electromechanical coupling factors by measuring third-tone and higher-tone series resonance frequencies. Experiments showed that the higher overtone ratio method has a distinct advantage over the measurement accuracy and the identity of the electromechanical coupling factor in comparison with the traditional overtone ratio method. To facilitate the application of the higher overtone ratio method, a table of the higher overtone ratio with the corresponding electromechanical coupling factors was provided.更多还原