采用丝网印刷工艺在PMNPT弛豫铁电单晶晶片表面涂覆了中温及高温两种银浆，通过快速烧结工艺分别在650和850 ℃条件下制备了银电极。采用扫描电子显微镜观察银电极表面及金属晶体界面的微观结构，采用能谱分析了界面的元素分布情况。银电极厚度为几十微米，呈多孔结构，与晶体结合良好。经过烧结后，晶体中的Pb、Nb、Ti等原子向银电极发生了迁移，而高温银浆烧结后在界面形成几微米厚的过渡层，晶体中原子向电极中的迁移大幅度减少。不同晶向的PMNPT晶片在高温下向银电极扩散过程中具有很强的晶面效应，［110］方向晶体中Pb、Nb、Ti原子向电极中的扩散程度小于［100］方向晶体。

弛豫铁电材料因具有高的介电常数和压电系数而广泛应用于致动器、换能器等领域。实际使用中往往需要施加大信号激励驱动谐振，因此了解掌握大信号激励下的谐振特性变化极为重要。然而，目前这方面的研究却少有文献报道。针对这一问题，以二步氧化物固相反应法制备了高压电性Pb0.9625Sm0.025［(Mg1/3Nb2/3)0.71Ti0.29］O3陶瓷材料，用本人搭建的大信号谐振响应测试系统研究了驱动场幅值和温度对径向谐振特性的影响。结果表明：低驱动场下谐振响应能保持单一谐振峰直至完全退极化，但随着驱动场的增大谐振响应变得复杂，即使在低温也呈现多个谐振峰。谐振特性的变化与机械品质因子Qm、铁电宏畴尺寸及相组成密切相关，低Qm材料在大驱动场下产生的内热加速了宏畴裂解并引发了二级铁电相变。谐振特性的不稳定及较大谐振频率温度系数限制了Sm改性PMN-PT弛豫铁电陶瓷的应用，尤其是在大信号下。

本文采用传统固相反应法, 成功制备了新型无铅弛豫铁电陶瓷(1-x)［0.9BaTiO3-0.1Bi(Mg0.25Ta0.5)O3］-xBi0.5Na0.5TiO3。结果表明, 较高居里温度的Bi0.5Na0.5TiO3的引入, 使得材料体系中建立了更多的以Bi-O耦合为主的极性纳米区域, 弥补了因Bi(Mg0.25Ta0.5)O3的加入导致的宏观极化强度的减少, 提高了材料的饱和极化强度, 实现了较高储能密度的同时具有更好的温度稳定性。在245 kV/cm电场强度下, x=0.2样品的储能密度约为4.01 J/cm3, 储能效率约为84.86%, 同时该组分在20~170 ℃储能密度的变化率小于5%, 储能效率的变化率小于6%, 表现出优异的温度稳定性。

The (1−x)(0.94Bi0.5Na0.5TiO₃–0.06BaTiO ₃)–xKTaO₃(BNBT–xKT) lead-free ferroelectric ceramics were produced using the traditional solid-state sintering technique, and the phase structure, surface morphology, electrical properties were all thoroughly examined. Every ceramic has a single perovskite structure and there is no second phase, as shown by the XRD patterns and Raman spectra. Scanning electron microscopy revealed that all samples displayed dense microstructure and cubic grain. In addition, KT encourages grain growth due to the oxygen vacancies induced by doping or volatilization of ions at high temperatures. The Tmof the ceramics decreases with increasing doping levels due to oxygen vacancies acting as dipoles upon the addition of KT, and the dielectric loss of all samples is low at ambient temperature. In comparison to the pure BNBT ceramic’s bipolar strain value of 0.12%, the BNBT–2KT ceramic achieved a maximum bipolar strain of ∼0.506% and unipolar strain of ∼ 0.430% with the corresponding d33*up to 538 pm/V under 80 kV/cm field. Performance significantly improved as a result of this. A test of the correlation between temperature and ferroelectric properties shows that the largest strain value of the BNBT–2KT ceramic occurs at ambient temperature and that the phase change from ferroelectric to relaxor is complete. Additionally, it is discovered that the BNBT–3KT ceramic can sustain a stable strain across a broad temperature range, suggesting that it has good temperature stability. The aforementioned findings demonstrate that lead-based ceramics may be replaced with BNBT–xKT ceramics.The (1−x)(0.94Bi0.5Na0.5TiO₃–0.06BaTiO ₃)–xKTaO₃(BNBT–xKT) lead-free ferroelectric ceramics were produced using the traditional solid-state sintering technique, and the phase structure, surface morphology, electrical properties were all thoroughly examined. Every ceramic has a single perovskite structure and there is no second phase, as shown by the XRD patterns and Raman spectra. Scanning electron microscopy revealed that all samples displayed dense microstructure and cubic grain. In addition, KT encourages grain growth due to the oxygen vacancies induced by doping or volatilization of ions at high temperatures. The Tmof the ceramics decreases with increasing doping levels due to oxygen vacancies acting as dipoles upon the addition of KT, and the dielectric loss of all samples is low at ambient temperature. In comparison to the pure BNBT ceramic’s bipolar strain value of 0.12%, the BNBT–2KT ceramic achieved a maximum bipolar strain of ∼0.506% and unipolar strain of ∼ 0.430% with the corresponding d33*up to 538 pm/V under 80 kV/cm field. Performance significantly improved as a result of this. A test of the correlation between temperature and ferroelectric properties shows that the largest strain value of the BNBT–2KT ceramic occurs at ambient temperature and that the phase change from ferroelectric to relaxor is complete. Additionally, it is discovered that the BNBT–3KT ceramic can sustain a stable strain across a broad temperature range, suggesting that it has good temperature stability. The aforementioned findings demonstrate that lead-based ceramics may be replaced with BNBT–xKT ceramics.

钙钛矿型(ABO3)弛豫铁电单晶具有优异的机电耦合性能, 被认为是研制下一代医疗超声换能器、高精度压电驱动器、水声换能器等机电耦合器件的核心关键材料。针对弛豫铁电单晶材料制备与物理性能方面尚存在的基础科学与工艺问题, 本文综述了近些年弛豫铁电单晶生长与性能优化方面的研究进展, 包括若干新的单晶生长方法用以改善弛豫铁电单晶的成分和性能均匀性, 提升弛豫铁电单晶压电性能的系列新方法, 通过铁电畴结构调控以获得高透光率的弛豫铁电单晶, 以及高性能弛豫铁电单晶在电光技术领域的应用等。

In this work, Ba1−xCaxTi0.88Zr0.12O₃ (x= 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around x= 0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials.In this work, Ba1−xCaxTi0.88Zr0.12O₃ (x= 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around x= 0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials.

In this study, the double-layered Aurivillius phases CaBi₂Ta₂O₉ (CBT) and PbBi₂Ta₂O₉ (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A2₁am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca2+ compared to Pb2+. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of A-site cations (Ca2+ and Pb2+) strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca2+ cations induced a higher structural distortion, which resulted in higher bandgap (Eg) energy and ferroelectric transition temperature (Tc) of CBT, compared to those of PBT.In this study, the double-layered Aurivillius phases CaBi₂Ta₂O₉ (CBT) and PbBi₂Ta₂O₉ (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A2₁am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca2+ compared to Pb2+. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of A-site cations (Ca2+ and Pb2+) strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca2+ cations induced a higher structural distortion, which resulted in higher bandgap (Eg) energy and ferroelectric transition temperature (Tc) of CBT, compared to those of PBT.

弛豫铁电单晶Pb(In1/2Nb1/2)O3-PbTiO3(PIN-PT)相较于常用的Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT)具有更高的居里温度, 在高稳定性、高性能的传感器、换能器方面具有应用前景。本工作采用谐振法研究了［001］方向极化的0.66PIN-0.34PT铁电单晶的全矩阵机电性能参数。0.66PIN-0.34PT 单晶的三方-四方相变温度(TRT)约为160 ℃, 居里温度(TC)约为260 ℃, 室温压电系数d33、d31、d15分别为1 340 pC/N、-780 pC/N、321 pC/N, 介电常数εT33、εS33、εT11、εS11分别为2 700、905、2 210、1 927, 机电耦合系数 k33、k31、k15、kt分别为 87%、58%、38%、61%。其纵向压电常数(d33)和纵向机电耦合系数(k33)小于 PMN-PT 单晶, 但是横向压电性能(d31)和剪切压电性能(d15)都略高于PMN-PT单晶。另外, 研究了机电耦合性能随温度的变化趋势, 发现0.66PIN-0.34PT单晶在150 ℃以下有较好的温度稳定性。

钛酸钡(BaTiO3)陶瓷作为传统的介质电容器材料，其强铁电性会导致储能密度低下，但通过掺杂可以削弱铁电性来获得弛豫铁电体，提高储能性能。利用铋系化合物可增强弛豫特性，本文设计了BiScO3和(Sr0.7Bi0.2)TiO3取代改性的BaTiO3基三元陶瓷材料: (0.99-x)Ba(Zr0.1Ti0.9)O3-x(Sr0.7Bi0.2)TiO3-0.01BiScO3(缩写为BZT-xSBT-BS)。采用传统固相法制备的BZT-xSBT-BS陶瓷，相结构没有因为掺杂发生改变，在室温下均为纯的三方相钙钛矿结构。介电和铁电的测试与分析表明，BZT-xSBT-BS陶瓷具有典型的弛豫铁电特性。由于不等价离子Sr2+、Bi3+的掺杂导致界面松弛极化，可以增大BZT-xSBT-BS陶瓷的介电常数，但是受制于其慢的响应速度，陶瓷的介电损耗也显著增加。适量(Sr0.7Bi0.2)TiO3可以提升BZT-xSBT-BS陶瓷的介电、铁电、应变和储能性能，x=0.015时的BZT-xSBT-BS陶瓷的综合性能较优: εr~10 372,tanδ~0.019,Pmax=16.42 μC/cm2，Ec=1.41 kV/cm，S+max=0.12%(@40 kV/cm),WD=0.181 J/cm3，η=80.4%(@60 kV/cm)。

为了满足低频高灵敏度声矢量接收需求, 提出并研制了一种具有层合梁结构的弛豫铁电单晶二维同振型矢量水听器。矢量通道分别由两个正交的单晶层合梁加速度传感器组成, 其中层合梁结构是通过在金属悬臂梁中引入阻尼层形成。通过有限元仿真分析了层合梁结构中单晶层厚度、阻尼层杨氏模量等参数对谐振频率及加速度灵敏度的影响。研制了多种加速度传感器及矢量水听器样品, 相关测试结果表明, 在材料上, 所提出的单晶传感器比压电陶瓷具有更高的灵敏度; 在结构上, 层合梁矢量水听器比金属梁具有更低的谐振频率和谐振峰, 在声压灵敏度及指向性凹坑方面均有3 dB的性能优势。