Ba(Zr0.3Ti0.7)O3 doping to enhance the dielectric and energy discharging performances of a 0.65Bi0.5Na0.5TiO3–0.35Sr0.7Bi0.2TiO3 lead-free ceramic

Journal of Materials Science: Materials in Electronics - A group of lead-free (1 ? x)(0.65Bi0.5Na0.5TiO3–0.35Sr0.7Bi0.2TiO3)–x[Ba(Zr0.3Ti0.7) O3]...     

铅对(Pbx,Sr1-x)0.85Bi0.1TiO3薄膜结构与介电可调性影响的研究

用溶胶-凝胶法制备了（Pbx，Sr1-x）0．85Bi0．1TiO3薄膜，对其晶相结构、微观形貌和介电可调性进行了研究．结果表明，该薄膜以钙钛矿形式存在．快速热处理过程可分解得到高活性离子，直接形成比相应温度平衡状态析晶时更多的晶相量．这种晶相在一定条件下有分解和再结晶的趋势．随着Pb^2＋离子增加和Sr^2＋离子减少，钙钛矿相的四方相与立方相间的转变温度升高．薄膜处在铁电相和顺电相转变点附近时，可以获得较大的可调性．     

Ferroelectric behavior in bismuth ferrite thin films of different thickness

The ferroelectric behavior of BiFeO(3) thin films is modified by changing the film thicknesses, where the BiFeO(3) thin films with different thicknesses were grown on SrRuO(3)/Pt/TiO(2)/SiO(2)/Si(100) substrates by radio frequency sputtering. The mixture of (110) and (111) orientations is induced for all BiFeO(3) thin films regardless of their thicknesses, together with the columnar structure and the dense microstructure. Their dielectric behavior is almost independent of the film thickness where all thin films have a low dielectric loss. A giant remanent polarization of 2P(r) ≈ 156.6-188.8 μC/cm(2) is induced for the BiFeO(3) thin films in the thickness range of 190-600 nm. As a result, it is an effective way to improve the ferroelectric behavior of the BiFeO(3) thin film by tailoring the film thickness.     

BST/BZT/BST多层薄膜结构与性能研究

利用脉冲激光沉积法在LaNiO3/LaAlO3(001)基片上生长了Ba0.6Sr0.4TiO3(BST)和Ba(Zr0.2Ti0.8)O3(BZT)单层薄膜,以及Ba(Zr0.2Ti0.8)O3/Ba0.6Sr0.4TiO3/Ba(Zr0.2Ti0.8)O3(BZT/BST/BZT)多层薄膜.X射线衍射(XRD)分析发现,BST、BZT和LNO薄膜都具有高度的(00l)取向.原子力显微镜(AFM)显示三种样品表面光滑无裂纹,晶粒尺寸和表面粗糙度相当.电容测试表明,相对BST、BZT单层薄膜,多层薄膜具有最大的品质因数42.07.表明多层薄膜在微波应用中具有很大的潜力.     

铋掺杂对SrTiO3薄膜微观结构及阻变行为的影响

采用溶胶-凝胶及快速退火工艺在p+-Si上制备了Bi掺杂SrTiO_3薄膜,构建了Ag/Sr_(1-x)Bi_xTiO_3/p+-Si结构阻变器件,研究了Bi掺杂量对薄膜微观结构、器件阻变行为及特性的影响。结果表明:Bi掺杂量较低时并未改变Sr_(1-x)Bi_xTiO_3薄膜的相结构,但随着掺杂比例的增大,晶粒尺寸也明显增大,当掺杂量x=0.16时,有Bi4SrTi4O15及TiO2相形成;不同Bi掺杂量的Ag/Sr_(1-x)Bi_xTiO_3/p+-Si器件均呈现出双极性阻变特性,且有明显的多级阻变行为。随Bi掺杂量的增加,器件的阻变性能逐步提高,当x=0.12时器件的高、低阻态电阻比值最大,达到105左右,并且在2 000次可逆循环测试下,高、低阻态电阻比未出现衰减,表现出良好的抗疲劳特性,但当掺杂量x达到或超过0.16后,器件的性能呈下降趋势。Bi掺杂量的增大会导致器件高阻态时的导电机制从空间电荷效应(SCLC)导电机制(x0.16)转变为肖特基势垒发射(x=0.16)。器件在低阻态下均遵循欧姆导电机制。     

Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown on thin Bi layer-coated Pt(111)/Ti/SiO2/Si substrates

In this work, the growth and study of dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown on thin Bi layer coated Pt(111)/Ti/SiO₂/Si substrates, depending on thin Bi layer thickness is reported. The BST thin film (thickness 180 nm) grown on 10-nm-thick Bi layer exhibited more improved structural and dielectric properties than that grown on bare Pt(111)/Ti/SiO₂/Si substrate. The 10-nm-thick Bi layer in optimum configuration was effective for the grain growth of BST phase and suppressed the formation of the oxygen-deficient layer at the interface between the BST thin film and bottom electrode, which resulted in an increase in dielectric constant and a decrease in leakage current density of the Pt/BST thin film/Pt capacitor.     

Strain-induced structural,magnetic and ferroelectric properties of heterostructure BST–NZFO nanocomposite thin film at room temperature

Heterostructure \(\hbox {Ba}_{0.7}\hbox {Sr}_{0.3}\hbox {TiO}_{3}\)–\(\hbox {Ni}_{0.8}\hbox {Zn}_{0.2}\hbox {Fe}_{2}\hbox {O}_{4}\) composite thin films grown on Pt–\(\hbox {TiO}_{2}\)–\(\hbox {SiO}_{2}\)–\(\hbox {Si}\) substrate were prepared by chemical solution process, where \(\hbox {Ba}_{0.7}\hbox {Sr}_{0.3}\hbox {TiO}_{3}\) layer grew as top/bottom while \(\hbox {Ni}_{0.8}\hbox {Zn}_{0.2}\hbox {Fe}_{2}\hbox {O}_{4}\) layer grew as bottom/top. Structural characterization by X-ray diffraction and atomic force microscopy showed the similar crystal structure, different lattice parameters, large lattice strain and small grain size in heterostructures, whatever their deposition sequences. Such heterostructures present simultaneously ferromagnetic and ferroelectric responses at room temperature. In particular, an exceptionally large saturation magnetization was observed in one heterostructures film. The growth sequences of \(\hbox {Ba}_{0.7}\hbox {Sr}_{0.3}\hbox {TiO}_{3}\) and \(\hbox {Ni}_{0.8}\hbox {Zn}_{0.2}\hbox {Fe}_{2}\hbox {O}_{4}\) layers on the substrate remarkably affect the magnetic properties of the composite thin films at room temperature.     

Ba0.7Sr0.3TiO3铁电薄膜的弥散相变特征及有序微畴

Ｂａ０．７Ｓｒ０．３ＴｉＯ３铁电薄膜的介电温谱呈现弥散相变的特征,相对介电常数与温度呈现平方关系。ＴＥＭ观察表明,１０ｎｍ量级微畴随机分布在晶粒中,选区电子衍射（ＳＡＥＤ）揭示微畴区存在１／２{201}超点阵,Ｂａ＾２＋、Ｓｒ＾２＋离子层在「００１」方向的交替排列可以描述该超点阵。     

DC bias-dependent shift of the resonance frequencies in BST thin film membranes

Direct current (DC) bias-dependent acoustic resonance phenomena have been observed in micromachined tunable thin film capacitors based on Ba(0.3)Sr(0.7)TiO3 (BST) thin films. The antiresonance frequency is only weakly DC bias dependent, and the resonance frequency exhibits a much stronger dependence on the applied DC bias. The resonance frequency shifted by 1.2% for a frequency of about 6.7 GHz and an applied field of 667 KV/cm. At the same time the effective electromechanical coupling constant k(2)(t,eff) increased to 2.0%. The tuning of the resonance frequency depends on the tunability of the film permittivity and on the mechanical load on the piezoactive layer. The experimental observations correlate well with the theoretical predictions derived from the free energy P expansion using Landau theory.     

不同退火方式对0.7BiFeO3-0.3PbTiO3薄膜的铁电性能及漏电流的影响

利用溶胶凝胶法在LaNiO3/SiO2/Si衬底上制备了0.7BiFeO3-0.3PbTiO3(BFPT7030)薄膜,研究了快速退火及常规退火两种不同的后续退火处理方式对薄膜铁电性能及漏电流性能的影响.XRD测试表明,经快速退火处理的BFPT7030薄膜结晶完好,呈现出单一的钙钛矿相.SEM测试结果显示,经快速退火处理的BFPT7030薄膜结晶充分,但经常规退火处理的BFPT7030薄膜表面致密性较好,且在升温速率为2℃/min时薄膜的晶粒更细小.经快速退火处理的BFPT7030薄膜的铁电性能较为优异,在升温速率为20℃/s时,其剩余极化Pr为22μC/cm2,矫顽场Ec为70 kV/cm,并具有较小的漏电流.XPS测试结果表明,经常规退火处理的BFPT7030薄膜其铁离子的价态波动较小.     

铁电钛酸锶钡薄膜的最新研究进展

铁电钛酸锶钡(BaxSrl-xTiO3)是一种拥有十分优越铁电／介电性能的材料，在可调谐微波器件及动态存储器件方面具有很好的应用前景．本文概括介绍了BaxSr1-x-TiO3薄膜的研究意义、基本结构、制备方法、各种性能特征及其表征方法与应用展望，并对当前BaxSr1-xTiO3薄膜研究中的几个重要前沿问题进行了详细讨论．     

BiFeO_3薄膜的液相自组装制备与表征

利用自组装单层膜技术,以三氯十八烷基硅烷(OTS)为模板,以硝酸铋和硝酸铁为原料,柠檬酸为络合剂,在玻璃基片上制备了铁酸铋晶态薄膜.探讨了薄膜的煅烧温度和沉积温度对BiFeO3薄膜的影响.通过X射线衍射(XRD)、扫描电镜(SEM)及原子力显微镜(AFM)测试手段对BiFeO3薄膜的物相组成、显微结构和表面形貌进行了表征,EDS能谱测试为铁酸铋薄膜的化学组成提供了有力的证据.结果表明:利用自组装技术在600℃热处理后成功制备出了纯净的BiFeO3晶态薄膜,当沉积温度为70～80℃时铁酸铋薄膜结晶良好,样品表面均匀、致密.     

Exchange coupling and exchange bias in La0.7Sr0.3MnO3-SrRuO3 superlattices

La(0.7)Sr(0.3)MnO(3)-SrRuO(3) superlattices with and without nanometrically thin SrTiO(3), BaTiO(3) and Ba(0.7)Sr(0.3)TiO(3) interlayers were grown by pulsed laser deposition. Transmission electron microscopy studies showed coherent growth of La(0.7)Sr(0.3)MnO(3), SrRuO(3) and SrTiO(3) layers with atomically sharp interfaces, even if individual layers were as thin as one or two unit cells. In contrast, misfit dislocations and unit cell high interfacial steps were observed at the interfaces between BaTiO(3) and one of the ferromagnetic layers. The presence of the interlayers as well as these extended defects had a significant influence on the magnetic properties of the superlattices, especially on the antiferromagnetic interlayer exchange coupling between the La(0.7)Sr(0.3)MnO(3) and SrRuO(3) layers and the exchange biasing. Surprisingly, exchange biasing was found to increase with decreasing strength of the antiferromagnetic interlayer exchange coupling. This was explained by different magnetization reversal mechanisms acting in the regimes of strong and weak interlayer exchange coupling.     

Effect of top electrodes on photovoltaic properties of polycrystalline BiFeO3 based thin film capacitors

We investigated capacitors based on polycrystalline narrow-band-gap BiFeO(3) (BFO) thin films with different top electrodes. The photovoltaic response for the capacitor with a Sn-doped In(2)O(3) (ITO) top electrode is about 25 times higher than that with a Au top electrode, which indicates that the electrode plays a key role in determining the photovoltaic response of ferroelectric thin film capacitors, as simulated by Qin et al (2009 Appl. Phys. Lett. 95 22912). The light-to-electricity photovoltaic efficiency for the ITO/polycrystalline BFO/Pt capacitor can reach 0.125%. Furthermore, under incident light of 450 μW cm(-2) and zero bias, the corresponding photocurrent varies from 0.2 to 200 pA, that is, almost a 1000-fold photoconductivity enhancement. Our experiments suggest that polycrystalline BFO films are promising materials for application in photo-sensitive and energy-related devices.     

Effect of co-substitution of Na0.5Bi0.5TiO3 and CaTiO3 on the structure and properties of BiFeO3 ceramics

Journal of Materials Science: Materials in Electronics - Ion substitution was the most efficient way for BiFeO3 modification. In this work, polar Na0.5Bi0.5TiO3 and non-polar CaTiO3 were chosen to...     

La(1−x)SrxCoO3 for thin film thermocouple applications

In this study, the LSCO (lanthanum strontium cobalt oxide) family has been investigated for thin film thermocouple applications. Thin films of La_(1−x)Sr_xCoO₃ (x=0.3,0.5,0.7) were prepared on sapphire substrates by pulsed laser deposition. The films were annealed at different temperatures in air and characterized for phase, composition and microstructure to determine their thermal stability. From the phase and composition analyses, it is clear that as the Sr content in LSCO increases, the thermal stability decreases. Among the three compositions studied, x=0.3 had the best phase and chemical stability, and microstructural properties. It was observed that La_0.7Sr_0.3CoO₃ possesses excellent phase, composition and microstructural stability up to 1273 K. Above 1273 K, however, LSCO decomposes resulting in the loss of cobalt and formation of individual oxide phases. Electrical resistivity and Seebeck coefficients were measured in situ as a function of temperature in air up to 1023 K. The electrical and Seebeck coefficient properties were found to be stable for all the three compositions up to 1023 K and studies indicated that electrical conduction occurs through a small polaron hopping mechanism. In conclusion, LSCO possessed good thermal stability in air up to 1273 K and exhibits excellent potential in thin film thermocouple applications.     

Selective soft mode heating in a ferroelectric film

The effect of electromagnetic radiation with a frequency of f ～ 0.3 THz on the temperature of a soft-mode phonon subsystem in a (Ba,Sr)TiO₃ film has been studied. Features of the temperature regimes in a ferroelectric capacitor structure were revealed using a capacitive thermometer and a thermocouple. It is established that, at a pumping radiation intensity of ～6 mW/mm², the overheating of soft-mode phonons, as evaluated from a change in the capacitance of a planar capacitor, exceeds the integral overheating of this capacitor measured using a thermocouple. Conditions determining the nonequilibrium state of the soft-mode phonon subsystem in a ferroelectric film are analyzed.     

Cation off-stoichiometric SrMnO<Subscript>3−δ</Subscript> thin film grown by pulsed laser deposition

The laser energy density (laser fluence) dependency of the Sr/Mn ratio was investigated for SrMnO_3−δ (SMO) thin films grown by pulsed laser deposition (PLD). It was found that the Sr/Mn ratio showed a steep increase followed by a gradual increase as the laser fluence was increased. However, the Sr/Mn ratio always showed Mn-excess under the present laser fluence condition as long as stoichiometric SrMnO₃ targets were used. In order to obtain cation stoichiometric SMO films, it was necessary to use Sr-excess SrMnO₃ targets in addition with laser fluence tuning. The crystal quality of the SMO thin film was found to vary with the Sr/Mn ratio. In stoichiometric or Sr-excess SMO thin films, epitaxial thin films could be obtained, whereas Mn-excess thin films showed very low crystallinity. Sr-excess films were also found to have some extra SrO planes. In addition, they exhibited out-of-plane lattice expansion which electron energy loss spectroscopy analysis revealed was due to Mn vacancies. The variation of film growth was closely related to point defects due to excess cations included in growing thin films.     

CSD法在亲水性的FTO基板上制备BiFeO3薄膜及其电性能的研究

利用化学溶液沉积法在亲水性的FTO基板上制备BiFeO3薄膜。利用XRD、FE-SEM、XPS、Agi-lent E4980A精密LCR仪及TF-Analyzer2000等分析手段对BiFeO3薄膜进行表征。结果表明,薄膜为纯相的结晶良好的多晶BiFeO3薄膜,由100～300nm的BiFeO3晶粒紧密的堆积而成,表面均匀平整。薄膜厚度为450nm。Fe的氧化态为Fe3+,并没有Fe2+出现。在10kHz时,介电常数和损耗分别为134和0.005。薄膜的剩余极化率为0.58μC/cm2,在0～250kV/cm的测试电场下漏导电流步伐保持在10-6 A/cm2以下。     

Synthesis and electrical properties of (Bi(1/2)Na(1/2))TiO3 (BNT) ferroelectric thin films by liquid sprayed mist chemical vapor deposition technique

This study aims to synthesize lead-free ferroelectric material, (Bi(1/2)Na(1/2))TiO3 using the Liquid Sprayed Mist Chemical Vapor Deposition (LSMCVD) technique. The mist of precursor solution was vaporized and deposited on two different substrates of Si(100) and (111)Pt/TiO2/SiO2/Si(100) in an oxygen atmosphere. The deposition temperature and time were varied in the range of 400-600 degrees C and 30-90 min. (Bi(1/2)Na(1/2))TiO3 thin film had preferred orientations of (110). The thickness of the thin film deposited was 35-162 nm. The remnant polarization (2Pr) and the dielectric constant were 4.6-16.8 microC/cm2, 325-350, respectively.