弛豫型铁电体PZNT制备与性能研究的进展

本文综述了近年来国际上弛豫型铁电体PZNT的制备与介电、压电及电致伸缩性能研究的进展．PZNT单晶体的制备方法以高温PbO熔剂法为主,其尺寸已达40mm．随PT含量的变化,PZNT的顺电一铁电相交由弥散性、混合型变为一级相变;其铁电-铁电相变可由组份或电场诱导,由介电性能表征．压电性能在MPB处及偏向三方相一侧达到最佳,＜001＞切向的三方相与四方相单晶可分别作为频带宽、分辨率高、且阻抗匹配好的新一代声阵列与单个器件传感器．＜001＞向的PZNT单晶具有巨大的电致伸缩应变,可望成为高性能的固体驱动器．     

弛豫铁电单晶及织构陶瓷的研究进展

综述了近年来弛豫铁电单晶和织构陶瓷的制备及其介电、压电性能的研究进展。弛豫铁电单晶的制备方法主要有高温溶液法、布里奇曼法和固态再结晶法，尺寸可达40mm以上，(001)切片压电常数d33最大可达3000pC／N，k3达到0.93，但是成分不均匀仍是影响晶体压电性能的一个主要因素。织构陶瓷的制备方法主要为固态再结晶法(TGG法和RTGG法)，其耗时短、成本低，压电性能可达到单晶的60％～80％，介电常数甚至可以超过部分单晶，是一个新的发展方向。     

Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3压电单晶的弛豫反常

对用改进的Bridgman法生长的Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3(PZNT91/9)单晶用Laue衍射法和XRD衍射曲线定向,取(001)晶片研究材料的电学性能.结果表明,材料的介电性能呈现出明显的频率色散现象,随着测试频率的升高,介电常数的峰值温度出现反常,峰的位置向低温方向移动.用扫描电子显微镜和正交偏光显微镜研究了PZNT91/9单晶的电畴结构,发现规则排列的带状畴与杂乱分布的细畴并存.X射线荧光分析结果表明,在PZNT91/9单晶中存在着由成分分凝引起的组分变化.成分分凝引起的组分波动和电畴结构的复杂性导致了材料性能的不均匀性,并与材料铁电相变的弥散性特征相关.     

弛豫铁电单晶压差水听器有限元设计

分析了[001]切型PMNT弛豫铁电单晶各向异性的压电特性,利用有限元软件对PMNT弛豫铁电单晶压差水听器进行仿真计算,设计制作了压电三叠片压差水听器。仿真与测试结果表明:[001]切型PMNT弛豫铁电单晶可近似等效为横观各向同性材料,在轴对称结构压差水听器设计中具有一定的应用优势,压差水听器的测试结果与有限元仿真结果相符。     

{110}cub切型Pb(Mg1/3Nb2/3)O3-PbTiO3单晶铁电相变的研究

测试了PMNT68／32{110}cub切型单晶的介电、压电性能和电滞回线，发现单晶铁电性能与所施加的极化电场及单晶中PbTiO3含量的变化密切相关。研究结果表明，相结构的变化是引起铁电性能变化的主要原因，即在＜110＞取向施加电场诱导出来的正交相是本征亚稳的，它的稳定性不仅取决于所施加的极化电场大小，而且与单晶中PbTiO3含量的变化密切相关。     

Pb[（Zn1／3Nb2／3）0.91Ti0.09]O3压电单晶的驰豫反常

对用改进的Bridgman法生长的Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3（PZNT91／9）单晶用Laue衍射法和XRD衍射曲线定向，取（001）晶片研究材料的电学性能，结果表明，材料的介电性能呈现出明显的频率色散现象，随着测试频率的升高，介电常数的峰值温度出现反常，峰的位置向低温方向移动。用扫描电子显微镜和正交偏光显微镜研究了PZNT91／9单晶的电畴结构，发现规则排列的带状畴与杂乱分布的细畴并存，X射线荧光分析结果表明，在PZNT91／9单晶中存在着由成分分凝引起的组分变化。成分发凝引起的组分波动和电畴结构的复杂性导致了材料性能的不均匀性，并与材料铁电相变的弥散性特征相关。     

{110}cub切型Pb(Mg1/3Nb2/3)O3-PbTiO3单晶铁电相变的研究

测试了PMNT68/32{110}_cub切型单晶的介电、压电性能和电滞回线,发现单晶铁电性能与所施加的极化电场及单晶中PbTiO3含量的变化密切相关.研究结果表明,相结构的变化是引起铁电性能变化的主要原因,即在<110>取向施加电场诱导出来的正交相是本征亚稳的,它的稳定性不仅取决于所施加的极化电场大小,而且与单晶中PbTiO₃含量的变化密切相关.     

分凝对Pb(Mg1/3Nb2/3)O3-38%PbTiO3单晶的成分及介电、压电性能的影响

研究了用改进的Bridgman法生长的PMNT62/38单晶在其生长过程中的分凝现象,研究了分凝导致的成分不均匀及其对介电和压电性能的影响.XRFA分析表明,PMNT62/38单晶底部的PbTiO3(PT)含量为x=35.2mol％,而顶部的PT含量为43mol％.底部晶体(001),(110)和(111)三种切型的晶片加电场极化后,其介电和压电性能出现了异常的现象.(110)切型的压电模量最大,为1200pC/N;(111)次之,为789pC/N;(001)最低,为371pC/N.极化后的(110)和(111)晶片在室温、1kHz频率下的相对介电常数(两种切型的εr都在10000左右),约为(001)晶片(ε_r-5000)的1倍,并且介电常数在低温端有上升的趋势.     

分凝对Pb(Mg1/3Nb2/3)O3-38%PbTiO3单晶的成分及介电、压电性能的影响

研究了用改进的Bridgman法生长的PMNT62／38单晶在其生长过程中的分凝现象，研究了分凝导致的成分不均匀及其对介电和压电性能的影响。XRFA分析表明，PMNT62／38单晶底部的PbTiO3(PT)含量为x=35.2mol%，而顶部的PT含量为43mol%。底部晶体（001），（110）和（111）三种切型的晶片加电场极化后，其介电和压电性能出现了异常的现象。（110）切型的压电模量最大，为1200pC/N；（111）次之，为789pC/N；（001）最低，为371pC/N。极化后的（110）和（111）晶片在室温、1kHz频率下的相对介电常数（两种切型的εr都在10000左右），约为（001）晶片（εr-5000)的1倍，并且介电常数在低温端有上升的趋势。     

钛酸铅陶瓷的介电和极化翻转特性研究

以水热纳米粉为前驱粉料,采用传统烧结工艺在950℃制备了致密性高、具有亚微米尺寸晶粒的钛酸铅(PbTiO3)陶瓷,并对其介电温谱和压电响应特性进行了系统的研究。结果表明,PbTiO3陶瓷在低温下的相对介电常数与测试频率无关,在室温以上,随着频率的增加,介电峰值向低温方向移动;压电力显微镜研究结果显示PbTiO3陶瓷中具有明显的微区极化翻转,表明具有较好的铁电性能。     

Relaxor based ferroelectric single crystals for electro-mechanical actuators

 The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn_1/3Nb_2/3)O3−PbTiO₃ (PZN-PT) and Pb(Mg_1/3Nb_2/3)O₃−PbTiO₃ (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O₃ (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d₃₃’s ) >2200 pC/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k₃₃) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators. Received: 2 January 1997 / Accepted: 27 March 1997     

Relaxor-PT single crystals: observations and developments

Relaxor-PT based ferroelectric single crystals Pb(Zn?/?)Nb(?/?)O?-PbTiO? (PZNT) and Pb(Mg?/?)Nb(?/?)O?-PbTiO? (PMNT) offer high performance with ultra-high electromechanical coupling factors k?? > 0.9 and piezoelectric coefficients d??s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by T(RT)-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T(C), a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these <001>-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective T(C)/T(RT). In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling low-loss crystals with high coupling for high-power applications.     

三元陶瓷Pb(In1/2Nb1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3准同型相界附近组分的介电、铁电和压电性能

铅基复合钙钛矿铁电材料广泛应用于机电传感器、致动器和换能器。二元铁电固溶体Pb(Ni_1/3Nb_2/3)O₃- PbTiO₃(PNN-PT)由于其在准同型相界(MPB)区域具有优异的压电、介电性能而备受关注。然而较大的介电损耗和较低的居里温度限制了其在高温高功率器件方面的应用。本研究通过引入Pb(In_1/2Nb_1/2)O₃ (PIN)作为第三组元改善PNN-PT的电学性能, 提高其居里温度; 通过两步法合成了MPB区域的三元铁电陶瓷Pb(In_1/2Nb_1/2)O₃- Pb(Ni_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PNN-PT), 研究了其结构、介电、铁电和压电性能。制备的所有组分陶瓷具有纯的钙钛矿结构。随着PT含量的增加, 陶瓷结构从三方相转变为四方相。通过XRD分析得到了室温下PIN-PNN-PT体系的MPB相图。体系的居里温度由于PIN的加入得到了很大的提高, 更重要的是PIN的引入降低了PNN-PT体系的介电损耗和电导。MPB处的组分展现出了优异的电学性能, 室温下, 性能最优组分为0.30PIN-0.33PNN-0.37PT: d₃₃=417 pC/N, T_C=200 ℃, ε′= 3206, tanδ=0.033, P_r=33.5 μC/cm², E_C=14.1 kV/cm。引入PNN-PT的PIN第三组元使得体系的居里温度和压电性得到提高的同时降低了的介电损耗和电导率, 因此, PIN-PNN-PT三元铁电陶瓷在高温高功率换能器等方面具备一定的应用潜力。     

Enhanced ferro- and piezoelectric properties in (100)-textured Nb-doped Pb(ZrxTi1 − x)O3 films with compositions at morphotropic phase boundary

To develop high-performance piezoelectric films on conventional Pt(111)/Ti/SiO₂/Si(100) substrates, sol-gel-derived highly [100]-textured Nb-doped Pb(Zr_xTi_1 − x)O₃ (PNZT) thin films with different Zr/Ti ratios ranging from 20/80 to 80/20 were prepared and characterized. The phase structure, ferroelectric and piezoelectric properties of the PZNT films were investigated as a function of Zr/Ti ratios, and it was confirmed that there was distinct phase transition of the PNZT system from tetragonal to rhombohedral when the Zr/Ti ratio varied across the morphotropic phase boundary (MPB). The Nb-doped PZT films showed enhanced remanent polarization but reduced coercive field, whose best values reached 75 μC/cm² and 82 kV/cm, respectively at the composition close to MPB. In addition, the [100]-textured PNZT film at MPB also shows a high piezoelectric coefficient up to 161 pm/V. All these properties are superior to those for undoped PZT films.     

Top-cooling-solution-growth and characterization of piezoelectric 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 [PZNT] single crystals

A technique of top-cooling-solution-growth (TCSG) has been developed to grow the piezo-/ferroelectric perovskite single crystals of 0.955Pb(Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ [PZNT95.5/4.5]. The flux composition and concentration, and the thermal parameters have been optimized, leading to the growth of high quality PZNT crystals with a size up to 20 × 15 × 10 mm³. The perovskite crystals are found to form upon slow cooling down to 1020°C, while the undesirable pyrochlore crystals of Pb_1.5Nb₂O_6.5-type start growing upon further cooling from 1020°C to 950°C. By controlling the growth pathway, the formation of the pyrochlore phase can be avoided. The dielectric properties of the grown PZNT95.5/4.5 crystals have been measured as a function of temperature at various frequencies. Upon heating, the phase transition for the rhombohedral R3m to the tetragonal P4mm phase takes place at 132°C, while the tetragonal to cubic phase transition occurs at 160°C. The TCSG developed in this work provides an alternative technique to grow PZNT piezocrystals of medium size at low cost for transducer applications.     

新型铁电晶体铌镥酸铅-钛酸铅的生长与性能

采用顶部籽晶法生长了一系列不同组分的高居里温度铌镥酸铅-钛酸铅[(1-x)Pb(Lu_1/2Nb_1/2)O₃-xPbTiO₃ (PLN-xPT)]铁电晶体。该晶体在三方相区域表现出典型的介电弛豫特性, 不同组分的晶体表现出了较高的居里温度; 基于介电和结构测试结果, 得到了该体系的低温二元体系相图, 在相图中存在一个准同型相界区域(MPB), 其组分位于x = 0.49~0.51; 利用偏光显微镜分析晶体电畴结构得到和X射线粉末衍射测试结果吻合的相结构; 电学性能测试结果表明不同组分的晶体性能差异较大。组分位于MPB附近的晶体表现出优异的压电性能, 如x = 0.49时, 居里温度T_c = 360℃, 压电常数d₃₃ > 1600 pC/N。处于MPB附近的晶体存在较大的矫顽E_c >10kV/cm, 一些组分晶体的三方–四方相变温度T_RT > 200℃。结果表明高的居里温度及优异的压电性能使二元铌镥酸铅-钛酸铅晶体具有更大的温度应用范围及更广阔的应用前景。     

Construction of new morphotropic phase boundary in 0.94(K0.4?xNa0.6BaxNb1?xZrx)O3–0.06LiSbO3 lead-free piezoelectric ceramics

0.94(K_0.4−x Na_0.6Ba _x Nb_1−x Zr _x )O₃–0.06LiSbO₃ ceramics were prepared by conventional technique, and the effect of BaZrO₃ on the phase transitions, dielectric, ferroelectric, and piezoelectric properties of the ceramics were investigated. The phase transitions for the ceramics were determined by the temperature dependence of dielectric properties and X-ray diffraction patterns. BaZrO₃ changes the symmetry of the ceramics from tetragonal dominant phase with x = 0–0.06 to rhombohedral phase with x = 0.07–0.09. The phase transition near room temperature for the composition with x ~ 0.06 is different from previously reported phase transition between orthorhombic and tetragonal phases. It is suggested that a new morphotropic phase boundary (MPB) is constructed with both rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions near room temperature, and the enhanced piezoelectric properties (d ₃₃ = 344 pC/N and k _P = 32.4% with x = 0.06) are obtained. The results indicate that the construction of new MPB is of significance for further development of KNN-based ceramics.