La0.5Sr0.5CoO3/Pb(Zr0.4Ti0.6)O3/La0.5Sr0.5CoO3铁电电容器的结构和性能研究

采用磁控溅射法和脉冲激光沉积法,在SrTiO3(001)衬底上制备了La0.5Sr0.5CoO3(70 nm)/Pb(Zr0.4Ti0.6)O3(70 nm)/La0.5Sr0.5CoO3(70 nm) (LSCO/PZT/LSCO)铁电电容器异质结.X射线衍射结果表明:LSCO和PZT薄膜均为外延结构.在5 V的外加电压下, LSCO/PZT/LSCO电容器具有较低的矫顽电压(0.49 V),较高的剩余极化强度(41.7 μC/cm2 )和较低的漏电流密度(1.97×10-5 A/cm2),LSCO/PZT/LSCO电容器的最大介电常数为1073.漏电流的分析表明:当外加电压小于0.6 V时,电容器满足欧姆导电机制;当外加电压大于0.6 V时,符合空间电荷限制电流(SCLC)导电机制.     

含Ni-Nb阻挡层的硅基Pb(Zr0.4,Ti0.6)O3电容器的制备及铁电性能研究

采用Ni-Nb薄膜作为导电阻挡层,以La0.5Sr0.5CoO3(LSCO)为底电极,构建了LSCO/Pb(Zr0.4,Ti0.6)O3(PZT)/LSCO异质结电容器。使用X射线衍射仪和铁电测试仪对其进行结构表征和性能测试。实验发现:Ni-Nb薄膜为非晶结构,PZT薄膜结晶状况良好。LSCO/PZT/LSCO电容器在5 V外加电压测试下,电滞回线具有良好的饱和趋势,剩余极化强度Pr为35.5μC/cm2,矫顽电压Vc为1.42 V,电容器具有良好的抗疲劳特性和保持特性。     

(La0.5Sr0.5)CoO3为电极的Pb(Zr0.4Ti0.6)O3和Pb(Zr0.2Ti0.8)O3铁电电容器结构及电学性能

分别采用磁控溅射法和溶胶-凝胶法(Sol-gel)制备了(La0.5Sr0.5)CoO3(LSCO)和Pb(Zr1-xTix)O3(PZT)薄膜,在Pt(111)/Ti/SiO2/Si基片上构架了LSCO/Pb(Zr0.4Ti0.6)O3(PZT(40/60))/LSCO和LSCO/Pb(Zr0.2Ti0.8)O3(PZT(20/80))/LSCO铁电电容器,研究了两种铁电电容器的结构和性能。XRD结构分析表明:两种四方相的不同Zr/Ti比例的PZT薄膜均为结晶良好的多晶钙钛矿结构。在5 V测试电压下,LSCO/PZT(40/60)/LSCO和LSCO/PZT(20/80)/LSCO两种铁电电容器的剩余极化强度(Pr)和矫顽场(Ec)分别为:28μC/cm2和1.2 V以及32μC/cm2和2 V。相对于PZT(40/60),PZT(20/80)具有较大的剩余极化强度和矫顽场,是由于其矩形度(c/a)较大。两种电容器都具有较好的脉宽依赖性和抗疲劳性。在5 V的测试电压下,LSCO/PZT(40/60)/LSCO电容器的漏电流密度为3.2×10-5A/cm2,LSCO/PZT(20/80)/LSCO电容器的漏电流密度为3.11×10-4A/cm2,经拟合分析发现:在0～5 V的范围内,两种电容器都满足欧姆导电机制。     

退火工艺对含Ti-Al阻挡层的硅基Pb(Zr_(0.4),Ti_(0.6))O_3铁电电容器结构和性能影响的研究

应用非晶的Ti-Al薄膜为导电阻挡层,采用射频磁控溅射法和溶胶-凝胶法在Si衬底上制备了La_(0.5)Sr_(0.5)CoO_3/Pb(Zr_(0.4),Ti_(0.6))O_3/La_(0.5)Sr_(0.5)CoO_3/Ti-Al/Si (LSCO/PZT/LSCO/Ti-Al/Si)异质结,研究了550 ℃常规退火(CTA)和快速退火(RTA)工艺对LSCO/PZT/LSCO/Ti-Al/Si结构和性能的影响.实验发现非晶Ti-Al薄膜在经过不同退火工艺后仍具有非晶结构,快速退火6 min的样品具有较好的物理性能.在418 kV/cm的外加电场下,LSCO/PZT/LSCO电容器的剩余极化强度和矫顽电场强度分别为22 μC/cm~2和83 kV/cm.LSCO/PZT/LSCO电容器的漏电行为不依赖于退火工艺,当电场强度低于46.7 kV/cm时为欧姆导电,高于46.7 kV/cm时为肖特基导电机制.     

Pb过量对以Ti-Al为阻挡层的硅基铁电电容器极化翻转性能的影响

以射频磁控溅射法生长的La0.5Sr0.5CoO3( LSCO)为电极,采用溶胶-凝胶法在以Ti-Al为导电阻挡层的Si基片上生长了用不同Pb过量前驱体溶液(溶胶)制备的LSCO/Pb( Zro4Ti0.6)O3(PZT)/LSCO电容器,以此构造了Pt/LSCO/PZT/LSCO/Ti-Al/Si异质结.Pb过量对LSCO/PZT/LSCO电容器极化翻转性能的影响表明:不同Pb过量溶胶对电容器的极化翻转性能影响很大,其中Pb过量15;的溶胶制备的样品在550℃常规退火1h后相对具有较好的翻转性能.在5V的外加电场下,LSCO/PZT/LSCO电容器的矫顽电压和剩余极化强度分别为1.25V和24.6μC/cm2.疲劳和电阻率测试分析表明:在经过109翻转后,不同样品的抗疲劳性能均很好,而电阻率随前驱体溶液Pb过量的增加呈现下降的趋势.     

钙钛矿型氧化物电极对Ba0.6Sr0.4TiO3薄膜电学性能的影响

采用脉冲激光沉积技术(PLD)在单晶基片LaAlO3(001)、MgO(002)上分别制备Ba06Sr04TiO3/La0.5Sr05CoO3(BST/LSCO)、Ba0.6Sr04TiO3/SrRuO3 (BST/SRO)异质结构,研究了LSCO和SRO底电极对BST薄膜晶相结构、表面形貌及BST薄膜电容器的电学特性的影响.研究发现,沉积在钙钛矿氧化物底电极上的BST薄膜表面平整,并都具有良好的外延生长.由于生长在LSCO底电极BST薄膜的压应力大于生长在SRO底电极的压应力,BST/LSCO异质结构的介电可调率为79.58;,而BST/SRO的介电可调率仅为68.26;,两种底电极上生长的BST薄膜都具有较低的漏电流.     

PZT基反铁电材料研究进展

在综述Pb(Zr,Ti)O3(PZT)基反铁电材料的研制与性能研究进展的基础上,重点探讨了PZT95/5反铁电材料和在PZT基础上掺杂改性的Pb(Zr,Sn,Ti)O3(PZST),(Pb,La)(Zr,Sn,Ti)O3 (PLZST)反铁电材料.总结了利用La3+、Nb4+、Hf4+、Sr2+、Ba2+和Nd3+等离子对富锆PZT以及PZST粉体、陶瓷以及薄膜材料的掺杂取代改性研究.讨论了各类PZT基反铁电材料的铁电(FE)-反铁电(AFE)相变机理以及其场致应变性能.展望了PZT基反铁电材料今后研究与应用的发展方向.     

SrRuO3导电层对快速退火制备Pb(Zr,Ti)O3薄膜结构和性能的影响

采用溶胶-凝胶法在Pt/Ti/SiO2/Si基片上,制备了Pt/Pb(Zr,Ti)O3(PZT)/Pt和SrRuO3(SRO)/PZT/SrRuO3(SRO)异质结电容器,并研究了快速退火条件下SRO导电层对PZT结构和性能的影响.XRD测试表明,两种结构电容器中的PZT薄膜均为钙钛矿结构,SRO/PZT/SRO、Pt/PZT/Pt均具有较好的铁电性和脉宽依赖性,5 V电压下两电容器的剩余极化强度Pr和矫顽电压Vc分别为28.3 μC/cm2、1.2 V和17.4 μC/cm2、2.1 V.在经过1010次翻转后,SRO/PZT/SRO铁电电容器疲劳特性相对于Pt/PZT/Pt电容器有了较大的改善,但SRO导电层的引入也带来了漏电流增大的问题.     

硅基外延SrRuO3/PbZr0.5Ti0.5O3/SrRuO3电容器的结构和性能研究

传统的方法很难直接在硅衬底上制备外延的氧化物铁电电容器,本实验采用生长在硅衬底上的外延SrTiO3为模板,直接生长了SrRuO3/PbZr0.5Ti0.5O3/SrRuO3电容器异质结,并对其结构及性能进行了研究.X射线衍射表明所制备的SrRuO3/PbZr0.5Ti0.5O3/SrRuO3异质结实现了在硅衬底上的外延生长.在5V测试电压下,铁电电容器的剩余极化强度和矫顽电压分别为19.6μC/cm2和0.8V.当极化翻转次数达到1010时,铁电电容器的极化强度没有明显的衰减,表明SrRuO3/PbZr0.5Ti0.5O3/SrRuO3电容器具有良好的抗疲劳性能.     

溶胶-凝胶法制备Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷

采用凝胶预碳化处理工艺制备了颗粒粒径较小,无硬团聚的Ca0.4Sr0.6Bi4Ti4O15纳米粉体,以Ca0.4Sr0.6Bi4Ti4O15非晶团簇粉体为陶瓷素坯的原料,同组分高浓度的Ca0.4Sr0.6Bi4Ti4O15溶胶为粘结剂,制备了Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷,研究了Ca0.4Sr0.6Bi4Ti4O15粉体的相结构和微观形貌以及陶瓷的显微结构和铁电性能.实验结果表明:700 ℃焙烧粉体呈现为非晶团簇,800 ℃焙烧粉体形成了纯层状钙钛矿结构,粒径在100～150 nm之间,无硬团聚;950 ℃烧结的Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷结构致密,晶粒尺寸在0.2～0.5 μm之间,其铁电性能优良,剩余极化Pr=12.5 μC/cm2,矫顽场强Ec=50 kV/cm.     

Phase separation in La1−x Sr x CoO3 solid solutions with a perovskite structure

The properties of La_1−x Sr _x CoO₃ (x = 0, 0.15, 0.20, 0.30) solid solutions are investigated using neutron diffraction, positive-muon spin relaxation (precession) measurements, and extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy. The results obtained are interpreted within the model of phase separation into ferromagnetic regions enriched with Sr²⁺ ions and nonmagnetic regions similar in composition to the LaCoO₃ compound.

     

Phase Formation and Structure of (RE,M)2Ca0.5Sr0.5Cu2O6+δ (RE=La,Pr, M=Ca,Sr)

The samples of (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d are prepared by solid state reaction method. The single phase boundary of RE and M in (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d is 1.0 ∼2.0 and 0 ∼1.0 respectively. In (Pr,M)₂Ca_0.5Sr_0.5Cu₂O_6+d, the phase boundary of Sr is 0 ∼1.0. The structure of (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d belongs to the structure type of 212 cuprate superconductors with space group I4/mmm.     

Microwave dielectric properties of La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics

This study examined the potential applications of microwave dielectric properties of La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics in rectenna. The La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm³, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

0.6Ca0.61La0.26TiO3-0.4La(Mg0.5Ti0.5)O3介质陶瓷微波烧结的晶粒生长动力学研究

采用微波烧结制备了0.6Ca0.61La0.26TiO3-0.4La(Mg0.5Ti0.5)O3[0.6CLT-0.4LMT]陶瓷,研究烧结工艺对其显微结构和晶粒生长行为的影响,并采用线性回归方法建立了Hillert模型和Sellars简化模型,采用非线性回归方法建立了具有时间指数的Sellars-Anelli模型.结果 表明,随着烧结温度的升高、保温时间越长,晶粒尺寸越大,且烧结温度对晶粒生长的影响更为明显.对三种模型预测的晶粒尺寸与实验结果的平均晶粒尺寸进行了误差分析,发现Hillert模型对该陶瓷的预测精度最低,Sellars-Anelli模型对该陶瓷的预测精度最高.由Sellars-Anelli模型得到的0.6CLT-0.4LMT陶瓷的晶粒生长动力学方程为d4.718=d04.718 +4.516×1033×t0.888×exp[-1 059 682/(RT)],能够有效预测0.6CLT-0.4LMT陶瓷微波烧结的晶粒生长过程.     

Electro‐optic,Piezoelectric and Dielectric Properties of Langasite (La3Ga5SiO14), Langanite (La3Ga5.5Nb0.5O14) and Langataite (La3Ga5.5Ta0.5O14)

Refractive indices were determined of single crystals of La₃Ga₅SiO₁₄ (langasite, LGS), La₃Ga_5.5Nb_0.5O₁₄ (langanite, LGN) and La₃Ga_5.5Ta_0.5O₁₄ (langataite, LGT) in the wavelength region between 0.36 μm and 2.33 μm. While phase‐matched optical second harmonic generation is not possible in LGS it occurs in the isotypic compounds LGN and LGT. Temperature‐dependent examination of the dielectric properties of LGS up to 600 °C showed anomalous behaviour. For all three substances the electro‐optic [r^σ_ijk] (“unclamped”) and the piezoelectric [d_ijk ] tensors were determined at room temperature. In addition, the temperature‐dependence of these properties was studied for LGS between –200 °C and +200 °C by a Jamin interferometer in combination with a modified Sénarmont compensator.     

(Ba0.5Sr0.5)Nb2O6基玻璃添加对BiFeO3陶瓷多铁性能的影响

采用固相法制备BiFeO3-x[BSN-G](x=0～5.0wt;)陶瓷样品,研究添加不同量的BSN-G对BiFeO3陶瓷微观形貌,电性能及磁性能的影响.研究结果表明:BSN-G的加入使得陶瓷样品气孔率降低,致密度提高.随着x的增加,陶瓷的介电常数和介电损耗呈逐渐降低趋势,当x=5;时,样品在1 kHz频率下的介电损耗为0.003.此外,添加BSN-G使得BiFeO3陶瓷的漏导电流降低,x=5;的样品具有饱和的电滞回线,其饱和极化强度Ps为1.5 μC/cm2,漏导电流密度J为0.39×10-6 A/cm2.交流阻抗图谱分析表明随着x的增加,样品的电阻呈增大趋势.活化能Ea随x增加而依次降低,进一步说明其损耗呈逐渐降低趋势.随着x的增加,样品的磁性能得到一定改善.     

0.6(Na0.5Bi0.5)TiO3-0.4(Bi0.1Sr0.9)TiO3无铅压电陶瓷的铁电性和阻抗谱研究

采用传统固相法制备了0.6(Na0.5Bi0.5)TiO3-0.4(Bi0.1Sr0.9)TiO3陶瓷(即6BNT-4BST-9),研究了其相结构、铁电性能和储能特性;且利用复阻抗谱和电模量谱分析了其电性能.结果表明:(1)6BNT-4BST-9陶瓷在室温时具有三方和四方共存的相结构;P-E回线和S-E曲线分析表明陶瓷中由非极性四方相占据主导.(2)6BNT-4BST-9陶瓷具有较大Pmax～18.2μC/cm2,和较小的Pr～1.0μC/cm2;它在低场下的储能特性为W1=0.313 J/cm3,η=85.3;(@40kV/cm).(3)M″-f和(-Z″)-f曲线在同一位置的特征峰表明对于6BNT-4BST-9陶瓷只有一种材料微区对电性能起主导.6BNT-4BST-9陶瓷具有负温度系数的电阻-温度特性;根据Arrhenius Law计算的激活能Ea=1.48 eV,表明该陶瓷具有电子导电特征.     

Microwave dielectric properties of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system with a near zero temperature coefficient of resonant frequency

In this study, the microwave dielectric properties of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system prepared by the conventional solid‐state method have been investigated for application in mobile communication. It was found that the diffraction peaks of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system shift to higher angles as x increases from 0.2 to 0.4. It was also found that the X‐ray diffraction patterns of the 0.8La(Mg_0.5Sn_0.5)O₃‐0.2(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramics exhibited no significant phase difference at different sintering temperatures. The average grain size of the (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system decreased from 6.4 to 4.3 μm as the value of x increased from 0.2 to 0.4 sintered at 1550 °C for 4 h. The dielectric constant increased from 26.6 to 35.9 and the quality factor (Q×f) decreased from 31,600 to 23,300 GHz for (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system as the x value increases from 0.2 to 0.4 sintered at 1550 °C for 4 h. The average value of temperature coefficient of resonant frequency (τ_f) increased from ‐18 to +8 ppm/ K as the x value increases from 0.2 to 0.4. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)