Study of amorphous thin films of (Ti, Nb)O2 solid solutions by X-ray absorption at the Ti K edge

As the (Ti, Nb)O₂ amorphous thin films cannot be prepared under a self-supported form, we have recorded the X-ray reflectivity. A new program which allows extraction of the X-ray absorption from the reflectivity is briefly described. The correction of the anomalous dispersion effect is effective, particularly near the edge within 200 eV. Hence, it has allowed a comparison between the amorphous layers and the crystalline analogues for which the X-ray absorption has been recorded by transmission. In the amorphous state, the TiO₆ group is smaller than in the crystalline state because of the relaxation of the crystallographic constraints. The oxygen coordination octahedron is almost regular in the films. On the other hand, in both cases, an electron transfer takes place from Nb to Ti.     

Structure evolution and stoichiometry control of Pb(Zr, Ti)O3 thick films fabricated by electrospray assisted vapour deposition

Well-crystallized and stoichiometric Pb(Zr, Ti)O₃ (PZT) films, typically ∼5 μm thick, with pure perovskite-type rhombohedral structures have been successfully prepared via an electrospray assisted vapour deposition (ESAVD) method. Control of the deposition temperature within a narrow range of 300-400 °C resulted in films with the most desirable phases. PZT films with close stoichiometric match with the expected composition ratio and uniform element distribution were obtained by adding the appropriate levels of excess Pb in the precursor solutions. The annealed films were uniform, dense, compact and adherent to the substrates. The dielectric constant, ?_r, and loss tangent, tan δ, of the fabricated PZT films measured at 10 kHz were 442 and 0.09, respectively. The ESAVD deposited PZT films showed a remanent polarization, P_r, of 15.3 μC/cm² and coercive field, E_c, of 86.7 kV/cm. These results demonstrate the clear potential of the ESAVD method as a promising technique for the fabrication of thick PZT films.     

柔性Pb(Zr_(0.53)Ti_(0.47))O_3薄膜的高温铁电特性

随着柔性电子产品的迅速发展,具有优异铁电和压电性的Pb(Zr_(0.53)Ti_(0.47))O_3 (PZT)薄膜在柔性的非易失性存储器、传感器和制动器等器件中有广泛的应用前景.同时,由于外部环境越来越复杂,具有高温稳定特性的材料和器件受到越来越多的关注.本文在耐高温的二维层状氟晶云母衬底上,用脉冲激光沉积技术制备出外延的PZT薄膜,并通过机械剥离的方法,得到柔性的外延PZT薄膜.研究了Pt/PZT/SRO异质结的铁电和压电性及其高温特性,发现样品表现出优越的铁电性,剩余极化强度(P_r)高达65μC/cm~2,在弯曲104次后其铁电性基本保持不变,且样品在275℃高温时仍然保持良好的铁电性.本文为柔性PZT薄膜在航空航天器件中的应用提供了实验基础.     

Generation of oxygen vacancies in the surface of ferroelectric Pb(Nb,Zr,Ti)O3

Controlled generation of oxygen vacancies in the surface of ferroelectric thin films is crucial to study how surface reduction affects molecular adsorption and catalysis of gas-surface phenomena. We demonstrate the effective reduction in the surface of 4% niobium doped 20/80 PZT (PNZT) thin films. The sample was characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), and heated at 200, 250 and 300 °C in a high vacuum system at 10⁻⁵ T of H₂. Auger peak-to-peak intensities was used to study the elemental concentrations during the reduction experiment. High-resolution XPS spectra were acquired before and after reduction process for detecting the changes of the oxygen signal. Vacancies production rates as slow as 0.21% per minute were achieved and the temperature was not a key parameter in the process. Experiments at higher hydrogen pressures and lower temperatures might improve the control of the vacancies production.     

铌镁酸铅-钛酸铅铁电阴极电子发射特性

研究了铌镁酸铅-钛酸铅铁电材料的铁电、介电性能对阴极发射阈值电压的影响, 以及铁电阴极发射电流与激励脉冲电压和抽取电压之间的关系, 并分析了其发射机理. 结果表明, 室温介电常数高、极化强度变化量大的弛豫铁电体0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃具有较小的发射阈值电压; 铁电阴极电子发射与快极化反转和等离子体的形成有关; 由极化反转所致电子发射的自发射电流随激励脉冲电压的增大呈幂律增长关系, 其发射电流开始于激励脉冲电压的下降沿; 在抽取电压较大时, 发射电流随抽取电压的增大呈线性增长关系, 说明大电流主要取决于抽取电压; 其发射电流开始于激励脉冲电压的上升沿, 与“三介点”处的场增强效应和等离子体的形成有关; 当抽取电压为2500 V 时, 得到的发射电流幅值为210 A, 相应的电流密度为447 A/cm².     

The ferroelectric and ferromagnetic characterization of CoFe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multilayered thin films

The multiferroic (PMN-PT/CFO)_n (n = 1,2) multilayered thin films have been prepared on SiO₂/Si(1 0 0) substrate with LNO as buffer layer via a rf magnetron sputtering method. The structure and surface morphology of multilayered thin films were determined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The smooth, dense and crack-free surface shows the excellent crystal quality with root-mean-square (RMS) roughness only 2.9 nm, and average grain size of CFO thin films on the surface is about 44 nm. The influence of the thin films thickness size, periodicity n and crystallite orientation on their properties including ferroelectric, ferromagnetic properties in the (PMN-PT/CFO)_n multilayered thin films were investigated. For multilayered thin films with n = 1 and n = 2, the remanent polarization Pr are 17.9 μC/cm² and 9.9 μC/cm²; the coercivity H_c are 1044 Oe and 660 Oe, respectively. In addition, the relative mechanism are also discussed.     

多孔未极化Pb(Zr0.95Ti0.05)O3铁电陶瓷单轴压缩力学响应与相变

通过添加造孔剂的方法制备了四种不同孔隙率未极化PZT95/5铁电陶瓷. 采用非接触式的数字散斑相关性分析(digital image correltation, DIC)全场应变光学测量技术, 对多孔未极化PZT95/5 铁电陶瓷开展了单轴压缩实验研究, 讨论了孔隙率对未极化PZT95/5铁电陶瓷的力学响应与畴变、相变行为的影响. 多孔未极化PZT95/5铁电陶瓷的单轴压缩应力-应变关系呈现出类似于泡沫或蜂窝材料的三阶段变形特征, 其变形机理主要归因于畴变和相变的共同作用, 与微孔洞塌缩过程无关. 多孔未极化PZT95/5铁电陶瓷的弹性模量、压缩强度都随着孔隙率的增加而明显降低, 而孔隙率对断裂应变的影响较小. 预制的微孔洞没有改善未极化PZT95/5铁电陶瓷材料的韧性, 这是因为单轴压缩下未极化PZT95/5铁电陶瓷的断裂机理是轴向劈裂破坏, 微孔洞对劈裂裂纹传播没有起到阻碍和分叉作用. 准静态单轴压缩下多孔未极化PZT95/5铁电陶瓷畴变和相变开始的临界应力都随着孔隙率的增大而呈线性衰减, 但相变开始的临界体积应变却不依赖孔隙率.     

Pb(Zr,Sn,Ti)O3反铁电陶瓷的低温相变扩散与极化弛豫

用弱场介电温谱、热释电流谱、强场电滞回线和变温X射线衍射谱研究了微量La掺杂Pb(Zr,Sn,Ti)O₃(PZST)反铁电(AFEt)陶瓷在-100—180℃温区内的结构与电学特性.弱场介电温谱显示,AFEt陶瓷在低温段(-100—50℃)呈现介电频率弥散(0.1—100kHz)和扩散型相变的特征,而变温X射线衍射谱却表明材料在这一温区内保持四方相结构;低温下经强场作用后,AFEt被诱导为亚稳三方铁电态,介电频率弥散消失.基于多元复杂化合物的组分起伏理论,讨论了PZST AFEt陶瓷 关键词： Pb(Zr Sn 3反铁电陶瓷')" href="#">Ti)O₃反铁电陶瓷 反铁电弛豫 相变 变温X射线衍射     

Pb(Zr_(0.4)Ti_(0.6))O_3电子结构的第一性原理研究

采用基于密度泛函理论的赝势平面波方法计算了Pb(Zr0.4Ti0.6)O3五层超晶胞的顺电相和铁电相的电子结构.由态密度、电子密度和能带结构的计算结果发现顺电相下钛氧八面体Ti-O6和锆氧八面体Zr-O6在铁电相中分裂为由1个O1离子和4个O2离子组成的金字塔结构Ti-O5和Zr-O5;与顺电相相比,铁电相中钛离子的3d电子和氧离子的2p电子存在更强的轨道杂化,这种杂化降低了离子间的短程排斥力,使得具有铁电性的四方结构更为稳定,而且钛离子与氧离子的相互作用对于铁电相Pb(Zr0.4Ti0.6)O3沿c轴自发极化的贡献大于锆离子与氧离子的相互作用;由电子密度的分布可推断立方结构的Pb-O键呈现离子键特征,而铁电相下Pb-O键则有较大的共价成分,铅离子与氧离子的这种轨道杂化对Pb(Zr0.4Ti0.6)O3的铁电性起重要作用.所得结果对深入理解Pb(Zr0.4Ti0.6)O3铁电性的微观机理具有参考价值.     

微秒脉冲电场下Pb_(0.99)(Zr_(0.95)Ti_(0.05))_(0.98)Nb_(0.02)O_3陶瓷击穿过程电阻变化规律

陶瓷作为应用非常广泛的一种材料,其电击穿问题一直是研究的重点和热点.由于击穿过程涉及热、光、电多场耦合效应,目前还没有一个普适的模型能够解释陶瓷击穿问题.针对此问题进行分析,实验中采用脉冲高压发生装置击穿陶瓷,通过对陶瓷击穿过程中等效电阻的研究,揭示了PZT95/5陶瓷样品体击穿和沿面闪络形成过程的异同.结果显示,在两种击穿模式下,陶瓷样品内部均会在40 ns左右形成导电通道,陶瓷等效电阻急剧下降至10~5?量级;然后体击穿与沿面闪络的导电通道以不同的速率继续扩展;电阻减小速率与导电通道上载流子的浓度有关,二者的等效电阻以不同速率减小,直至导电通道达到稳定.     

Pb(Zr,Sn,Ti)O3反铁电陶瓷场诱相变性能的改进

为了获得场诱反铁电(AFE_t)—铁电(FE_Ｒ)相变临界电场E_{f小、电滞ΔE小、场致应变x适当的反铁电陶瓷,对Pb(Zr, Sn, Ti)O3采用Ba ^2＋置换Pb^2＋,同时在四方反铁电相AFEt—三方铁电F EＲ相界附近调节Ti/Sn比,来控制FEＲ-AFEt,AFEt关键词： Pb(Zr Sn 3基反铁电陶瓷')" href="#">Ti)O3基反铁电陶瓷 场诱相变 场致应变 掺杂改性}     

Effect of excess Pb on crystallinity and ferroelectric properties of PZT(40/60) films on LaNiO3 coated Si substrates by MOD technique

Pb(Zr_0.4Ti_0.6)O₃ [PZT(40/60)] films were deposited onto LaNiO₃ (LNO) coated Si substrates by metal-organic decomposition (MOD) technique. Excess Pb was incorporated in the film by using excess Pb (2%–15%) in the solution. The crystallinity and ferroelectric properties of PZT films were investigated by using X-ray diffraction (XRD), RT66A test system and HP4194 impedance analyzer, respectively. Rayleigh law was employed to analyze the defect concentration in the films. The results show that all the PZT films show the (1 0 0) preferential orientation with complete perovskite structure except for the 2% film displaying some pyrochlore phase. The (1 0 0) preferential orientation is mainly attributed to LNO bottom electrode, which has the highly (1 0 0) preferential orientation. The 10% film shows the best polarization and dielectric properties. The remnant polarization and coercive field are about 10.1 μC/cm² and 73 kV/cm under an electric field around 330 kV/cm, respectively. And the dielectric constant and dissipation factor are about 656 and 0.022 at a frequency of 1 kHz, respectively. The good ferroelectric properties of the 10% film are mainly attributed to the low defect concentration in the film.     

溶胶-凝胶法制备Pb(Zr1?xTix)O3复合梯度薄摸以及介电与热释电特性

"在Pt/Ti/SiO2/Si基片上用溶胶-凝胶法生长制备了PZT(Pb(Zr1-xTix)O3)复合梯度铁电薄膜． 薄膜最终结构由6层组成,"向上"梯度薄膜在Pt底电极上的第一层从PbZrO3开始,顶层是PZT(50/50),即第一层是PbZrO3,第二层PZT90/10 (10%Ti),第三层是PZT80/20,第四层PZT70/30,第五层PZT60/40,第六层PZT50/50．每一层与此相反的是"向下"梯度PZT薄膜．用X射线衍射、俄歇电子能谱和阻抗分析来研究梯度薄膜的结构与介电特性．600     

Phase compositions and ferroelectric properties of Pb(Zr0.52,Ti0.48)O3 thin films with different highly orientations prepared by a sol-gel route

It is shown that different highly oriented Pb(Zr_0.52,Ti_0.48)O₃ films can be obtained on Pt/Ti/SiO₂/Si substrate using a sol-gel technique. The effects of pyrolysis temperature on the orientation, phase composition and ferroelectric properties of the films are investigated. It is found the ferroelectric hysteresis loops of (1 1 1)-oriented film, (1 1 1) and (1 0 0) mix-oriented film can both be saturated when the external electric field is large enough, whereas the hysteresis loop of (1 0 0)-oriented film is difficult to saturate. The analysis of X-ray diffraction indicated the possibility of different phase composition in different oriented films under large film residual stress. Higher remnant polarization (53 μC/cm²) for (1 0 0)-oriented film can be attributed to its more tetragonal phase composition, which results in that the in-plane domain switching can continuously occur with external electric field increasing.     

Effect of different annealing methods on ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3-0.05PbTiO3 thin films

0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films were prepared on LaNiO₃/SiO₂/Si substrate by radio frequency magnetron sputtering, and the films were annealed subsequently with repeated many times by two approaches: normal one-step rapid thermal annealing and innovative two-steps rapid thermal annealing. X-ray diffraction demonstrates that all the films were preferred (1 0 0) oriented and an appropriate repeat of annealing process can enhance perovskite phase of the films. Scanning electron microscopy suggests that the films treated by two-steps rapid thermal annealing show crack-free, uniform size grains and dense microstructure. Measurement of remnant polarization and leakage current dependence of electric field confirms that the films treated by two-steps rapid thermal annealing exhibit better ferroelectric properties than the films treated by one-steps rapid thermal annealing. The results reveal that microstructure plays an important role in enhanced ferroelectric properties of the 0.95Pb(Sc_0.5Ta_0.5)O₃-0.05PbTiO₃ thin films.     

Enhanced dielectric and ferroelectric properties of Pb1−3x/2Lax(Zr0.5Ti0.5)O3 thin films with low lanthanum substitution

Effects of lanthanum (La) substitution (0.003 ≤ x ≤ 0.015) on the dielectric and ferroelectric properties of Pb(Zr_0.5Ti_0.5)O₃ thin films have been investigated. The films were synthesized on the Pt (1 1 1)/Ti/SiO₂/Si (1 0 0) substrates by a sol-gel method. Large dielectric constants of the films are obtained within range of 800-1600 which are almost comparable to those observed in bulk ceramics. The films also show improved remnant polarization values and reduced coercive field values with the increasing addition of La substitution. Our results suggest that low La substitution contributes to enhance film electric properties due to the improvement of non-180° domain wall mobility as well as the stabilization of tetragonal phase.     

Thickness effect in Pb(Zr0.2Ti0.8)O3 ferroelectric thin films grown by pulsed laser deposition

Epitaxial Pb(Zr_,Ti)O₃ (PZT) thin films with thicknesses in the range of 50-200 nm and with 0.2 Zr/(Zr + Ti) ratio, were grown by pulsed laser deposition (PLD).The substrates used for PLD deposition are single crystalline 0.5% Nb-doped (1 0 0) SrTiO₃ (STON). SrRuO₃ (SRO) thin films were deposited as bottom and top electrodes in order to have minimum structural misfit, to insure on one side high quality growth, and on the other side to minimize the influence of the extended structural defects. Structural and electrical characterization was performed. The epitaxial PZT films are c-axis oriented and have an average roughness of 0.4 nm. The ferroelectric behavior was proved in all investigated films by the presence of the hysteresis loops and by the butterfly shape of the capacitance-voltage (C-V) characteristics. The ferroelectricity was present even in the samples with relative high leakage currents, down to a thickness of 50 nm. These results are essential when small thickness is needed for miniaturization of ferroelectric devices using PZT.     

Pb(Sc_(1/2)Nb_(1/2))O_3中有序-无序转变和铁电相变的Raman光谱研究

采用wolframite前驱物法制备了Pb(Sc1/2Nb1/2)O3陶瓷。通过调节陶瓷烧结工艺,获得了三种具有不同B位离子有序度的PSN陶瓷。测量了三种陶瓷样品在室温至160°C范围内的Raman光谱随温度变化。结果表明,随着温度的升高,三种不同B位有序度的陶瓷样品中,Raman光谱中位于530 cm-1的F2g模的峰位和半峰宽分别在100°C,85°C和80°C发生了突变,表明陶瓷分别在100°C,85°C和80°C三个温度点发生了铁电-顺电相变。上述结论得到了介电温度谱测量数据的支持。     

Shock-wave- and hydrostatic-pressure-induced depolarization of Pb(Zr,Sn,Ti)O3 for pulse power applications

Research on quasi-static pressure-induced depolarization illustrates that Pb(Zr,Sn,Ti)O₃ ceramic may be useful in the technology of pulse power. However, lack of knowledge on the shock-induced depolarization hinders this application. To fill this gap, we investigated the shock-wave- and hydrostatic-pressure-induced depolarization of Pb_0.99Nb_0.02[(Zr_0.90Sn_0.10)_0.96Ti_0.04]_0.98O₃ ceramic. In the hydrostatic experiment, complete and sudden depolarization took place at 140 MPa. Shock wave experiments in the normal and axial modes were conducted in the pressure range from 0.81 to 4.50 GPa. At 2.50 GPa, the phase transition occurred completely and the short-circuit current reached 32 A in the normal mode. We obtained 31.0 kV voltage, 0.96 MW and 0.92 J cm^?3 high-voltage pulse with 1000 Ω load. In the axial mode, the shape of the current pulse and its time integral were found to be strongly shock pressure dependent. Our work lays the foundation for the application of Pb(Zr,Sn,Ti)O₃ in the single-use power supply.     

不同衬底上Pb(Zr0.52Ti0.48)O3择优取向铁电薄膜的制备和研究

通过MOD法在Si(100)和Pt(111)/Ti/SiO₂/Si基片上制备出LaNiO₃ ( LNO)薄膜.再通过修 正的Sol-gel法，在Pt(111)/Ti/SiO₂/Si,LNO/Si(100)和LNO/Pt/Ti/SiO_{2< /sub>/Si三种衬底上 制备出具有择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜. 经XRD分析表明，L NO薄膜具有(100)择优取向的类钙钛矿结构；PZT薄膜均具有钙钛矿结构，且在Pt(111)/Ti/S iO2/Si衬底上的薄膜以(110)择优取向，在LNO/Pt/Ti/SiO2/Si和LN O/Si(100)衬底上的 薄膜以(100)择优取向.经场发射SEM分析和介电、铁电性能测试表明，在LNO/Si和LNO/Pt/Ti /SiO2/Si衬底上的PZT薄膜的平均粒径、介电常数以及剩余极化强度均比以Pt/T i/SiO2/Si为衬底的薄膜大. 关键词： 3}薄膜')" href="#">LaNiO₃薄膜 PZT铁电薄膜 择优取向 剩余极化强度