Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3-PbZrO3弛豫铁电晶体的生长及表征

采用高温溶液法生长了准同型相界(MPB)四元弛豫铁电单晶Pb(Sc1/2Nb1/2) O3-Pb(Mg1/3 Nb2/3)O3-PbTiO3-PbZrO3,得到较大尺寸且具有规则外形的立方单晶.研究结果表明所生长的晶体为钙钛矿结构,立方晶粒平整的暴露面均为(001)面;晶体以层状方式生长,生长机制为搭桥生长;所生长晶体的矫顽场Ec～3.52kV/cm,三方四方相变温度Tr-t～104℃,居里温度Tc～149.5℃,压电常数d33～1089 pC/N,剩余极化强度Pr～25.4 μC/cm2;随着频率增加,晶体的相变弥散度减小.     

三元铁电单晶Pb(Yb1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3-PbTiO3生长及性能表征

采用高温助熔剂法首次成功生长出了Pb(Yb1/2Nb1/2) O3-Pb(Zn1/3Nb2/3) O3-PbTiO3 (PYZNT)三元铁电单晶,并对晶体组分、介电、铁电和压电性能进行了研究.结果表明,晶体为纯三方钙钛矿相,实际组分为0.68PYN-0.22PZN-0.1PT.分别对晶体的介电,铁电和压电性能进行研究.介电常数ε'和介电损耗tanδ对温度和频率表现出典型的弛豫行为.晶体的居里温度TC为80℃.由于反铁电体PYN含量较高,晶体具有非常大的矫顽场,在100kV/cm的外电场条件下极化还不能反转,因而无法得到饱和的电滞回线.在未极化条件下,测得晶体的压电常数d33为78 pC/N.     

Pb(In1/2Nb1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3压电陶瓷的介电、铁电和压电性能

采用两步法制备了0.30Pb(In1/2 Nb1/2)O3-(0.70-x)Pb(Ni1/3Nb2/3)O3-xPbTiO3(PIN-PNN-PT,x=0.33,0.35,0.37,0.39)压电陶瓷.研究了PIN-PNN-PT压电陶瓷的相结构、介电、铁电和压电性能.研究表明位于准同型相界(MPB)的组分0.30PIN-0.33PNN-0.37PT具有最佳电学性能,其居里温度TC、压电系数d33、平面机电耦合系数kp、自由介电常数ε二介电损耗tanδ、剩余极化Pr、矫顽场EC分别为200℃、386 pC/N、50;、2692、0.045、34 μC/cm2、18 kV/cm.结果 显示PIN-PNN-PT三元系相比于PNN-PT有更高的居里温度,同时保持了优异的压电性能.     

稀土掺杂Pb(Mg1/3Nb2/3)O3-PbTiO3压电陶瓷的烧结特性研究

在传统的固相反应制备工艺中,固相反应的烧结温度直接影响着陶瓷的物相结构、陶瓷致密度以及介电性能等.本文采用固相反应法制备x; Sm3掺杂PMN-PT压电陶瓷,通过控制不同的烧结温度,制备了一系列Sm-PMNPT陶瓷样品.利用X射线衍射仪、介电温谱以及准静态d33测量仪对陶瓷结构、介电性能、压电系数等性能进行表征.研究结果表明:烧结温度在1250℃,x=1.875mol;～2.5mol;,陶瓷样品的钙钛矿含量最大,压电系数最高可达1254 pC/N,kp=0.58,相对介电常数高达30000左右,密度达到8.48 g/cm3.     

Nb2O5掺杂对Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3陶瓷组织与性能的影响

采用固相烧结法制备Nb2O5掺杂的Pb(Mg1/3Nb2/3) O3-PbZrO3-PbTiO3+ 0.5mol; ZnO(PMN-PZT)压电陶瓷,研究了不同Nb2O5掺杂量对材料结构及压电介电性能的影响.实验结果表明,随着Nb2O5掺杂量的增加(0～1 mol;),PMN-PZT陶瓷的晶界强度提高,断裂模式由沿晶断裂逐渐转变为穿晶断裂,而且陶瓷的压电介电性能升高.当Nb2O5掺杂量为1mol;时,1250℃烧结的陶瓷样品性能参数为:d33=430 pC/N,Qm=60,kp=0.52,kt=0.38,εr=3620,tanδ=0.017.     

REBa2Cu3O7-δ/MgO液相外延生长初始阶段的物理化学研究

本文综述了RE(RE＝Y,Nd)BCO高温超导体厚膜在MgO基片上液相外延生长(Liquid Phase Epitaxy,LPE)的初始阶段研究.外延生长初始阶段直接发生在种膜或者基片上,是整个生长过程最为特殊的阶段,对整个生长过程和晶体质量都有很大的影响.在不同生长条件下,探讨此阶段中熔体/厚膜/种膜/基板间的相互依赖关系及对生长机制的影响,包括:籽晶的部分溶化,基片的回溶,晶粒的优先溶化/生长, 熔体包裹物的形成以及异质种膜外延生长的机制等.     

外延生长四方相Pb(Zr0.65Ti0.35)O3薄膜

以SrRuO3(SRO)为缓冲层和底电极,利用射频溅射法在LaAlO3(LAO)单晶基片上制备了Pb(zr0.65Ti0.35)O3(PZT)薄膜.X射线衍射分析显示PZT薄膜与基底有以下外延取向关系:(001)[010]PZTⅡ(001)[010]SROⅡ(001)[010]LAO.虽然PZT薄膜组分位于菱方相区域,但由于基底的夹持效应,透射电子显微镜观察表明PZT薄膜呈现四方相.对以Pt或SRO为上电极的PZT薄膜的电性能分别进行了研究,结果显示两种样品都具有抗疲劳性,并且Pt/PZT/SRO薄膜电容与SRO/PZT/SRO薄膜电容相比具有更大的漏电流.氧化物基片和底电极的引入使得PZT薄膜的居里点与块材相比有所下降.电容-温度测试曲线表现出典型的居里-外斯定律特征,薄膜损耗随着温度上升而下降.当温度接近PZT薄膜相转变点的时候,由于夹持应力的解除导致薄膜损耗急剧下降.     

3C-SiC的液相外延生长及其结构的保持与分析

3C-SiC因其优越的物理和电学性能是制造耐高温、大功率、高频率器件的理想材料.本文报道了采用液相外延法从硅熔体中生长3C-SiC及抑制其相变的研究进展.采用X射线衍射、透射电镜、Raman散射等检测手段对样品进行结构分析,结果表明所制备的样品为3C-SiC单晶体.     

Bix（PrGdYb）3—x（FeAl）5O12晶体薄膜的助熔剂液相外延生长

本文介绍了采用助熔剂法和液相外延技术生长单晶薄膜的工艺技术。使用这种方法生长出了Ｂｉｘ（ＰｒＧｄＹｂ）３－ｘ（ＦｅＡｌ）５Ｏ１２磁光晶体薄膜，并测试了薄膜的磁光性能。     

BiFeO3-PbTiO3-Bi(Zn1/2Ti1/2)O3-PbZrO3高温压电陶瓷的电导机制研究

以传统陶瓷工艺制备了0.54BiFeO3-0.26PbTiO3-0.15Bi(Zn1/2Ti1/2) O3-0.05PbZrO3(BF-PT-BZT-PZ)高温压电陶瓷,采用交流阻抗谱技术,结合交流电导率的测试与分析,研究了陶瓷在高温下的电导行为.阻抗谱分析表明陶瓷的绝缘性能由晶粒和晶界共同贡献,其中晶粒激活能为0.75 eV,晶界激活能为1.83 eV.BF-PT-BZT-PZ陶瓷的电学等效电路可以用两个R-CPE并联电路串联构成.高温交流电导率的测试结果表明BF-PT-BZT-PZ的电导率随着温度的上升而增大,高温下其电导机制为离子电导,激活能为0.77 eV,主要载流子类型为氧空位.     

An effective growth method to improve the homogeneity of relaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3‐ Pb(Mg1/3Nb2/3)O3‐PbTiO3

Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In_1/2Nb_1/2)O₃‐Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (abbr. PIN‐PMN‐PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO₃ concentration constant during the crystal growth. As an example, the two‐round growth of ternary PIN‐PMN‐PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first‐round boule was used as the seed crystal for the second‐round growth. Our results show that the as‐grown (Ф80 mm × 270 mm) PIN‐PMN‐PT crystals exhibit higher phase transition temperatures (T_c∼180 °C, T_r/t∼110 °C) and larger coercive field (E_c∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ crystals, and similar dielectric and piezoelectric performances (ε∼5000, tanδ∼1.25%, d₃₃∼1500 pC/N, k_t∼60%). And about 85 percent of the crystal boule grown by the two‐round growth technique could maintain its compositions around the morphotropic phase boundary.     

Flux growth and low temperature dielectric relaxation in piezoelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals

Single crystals of Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT 91/9) have been grown by flux method after modifications in temperature profile, flux ratio and addition of excess ZnO/B₂O₃ which resulted in enhanced perovskite yield (more than 95%). Only a few crystals showed the presence of pyrochlore phase/variation in composition. A comparative characterization of these crystals were carried out in respect of piezoelectric charge coefficient d₃₃, dielectric constant, ac conductivity and hysteresis loop after cutting and poling the crystals along [001] direction. The total activation energy for conduction has been found to increase with Ti‐content in the sample. The effect of ZnO on growth behavior has been analyzed. A detailed analysis of PZNT (91:9) has been carried out at low temperature in respect of the various thermodynamic parameters related to the dielectric relaxation mechanism, like optical dielectric constant, static dielectric constant, free energy of activation for dipole relaxation, enthalpy of activation and relaxation time, have been calculated in the vicinity of transition temperature in the lower temperature region. The activation energy for relaxation at ‐10 and ‐49 °C have been found to be 0.09 and 0.02 eV respectively. The results were analyzed and a detailed dielectric analysis and low temperature relaxation behavior of PZNT crystals were interpreted. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pb(Mg1/3Nb2/3)O3-0.33PbTiO3晶体三方相的压电性能研究

以坐标系二次旋转为理论基础研究了PMN-0.33PT晶体三方相的常用压电模量d15、d24、d31、d33、d36和机电耦合系数k15、k24、k31、k33、k36在三维空间的变化规律.通过MATLAB编程求得以上各系数关于坐标系旋转角度的函数表达式,绘制出了它们的三维空间分布图,并一一求得这些系数的最大值,以及与最大值相对应的旋转角.发现除d33和k33外,d31、d36、k31和k36也在空间变化显著.d31和k31旋转后的最大值比原坐标系下的数值分别扩大了15倍和6倍,对应的旋转角分别为(-4.5°/90°)、(22.5°/270°).d36 和k36在原坐标系下不存在,经旋转后的最大值可分别达到1340 pC/N 和0.73.该研究结果对PMN-0.33PT晶体在压电传感器、换能器中的应用具有重要的理论价值.     

Refractive index dispersion of relaxor ferroelectric 0.9Pb(Zn1/3Nb2/3)O3‐0.1PbTiO3 single crystal

The refractive indices of 0.9Pb(Zn_1/3Nb_2/3)O₃‐0.1PbTiO₃ single crystal at different wavelengths have been measured by the minimum deviation method at room temperature, and their dispersion equations are obtained. The parameters connected to the energy band structure are obtained by fitting single‐oscillator dispersion equation. Despersion energies are found to take on covalent crystal values. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Domain structure and birefringence studies on a 0.91Pb(Zn1/3Nb2/3)O3 ‐0.09PbTiO3 single crystal

Domain structure and phase transition sequence of 0.91PZN‐0.09PT single crystal, grown from high temperature solution, have been analysed using polarised light microscopy. The domain structure of (001)_cub cut single crystal exhibit co‐existence of rhombohedral and tetragonal phases. The sequence and phase transition temperatures have been determined from temperature dependence of birefringence. Birefringence measurements during heating and cooling reveal a first order nature of phase transition between rhombohedral (R3m) and tetragonal (P4mm). The birefringence was measured with accuracy of 10^‐3. However, dielectric measurement does not provide any evidence of R3m ‐ P4mm phase transition. It is shown that in‐situ analysis of domain structure and phase transition can be used as non‐destructive analytical tool for determination of local composition and phase transition sequence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)