PbTiO3/PbZr0.3Ti0.7O3/PbTiO3夹心结构铁电薄膜子晶层的优化

用Sol-Gel法制备了Pb_(1+x)TiO₃/PbZr_03Ti_07O₃/Pb_(1+x)TiO₃(PT/PZT/PT)夹心结构及PZT铁电薄膜,为了获得高质量的PT/PZT/PT夹心结构铁电薄膜,使用不同过量Pb配比(x)的PbTiO₃ (PT)层进行制备,以获得优化的PT子晶层.X射线 关键词： PT/PZT/PT 夹心结构 子晶 铁电薄膜     

(Pb0.85Sm0.10)(Ti0.98Mn0.02)O3压电陶瓷超高各向异性机电耦合性能的X射线衍射研究

本文用X射线衍射技术研究了具有典型超高各向异性机电耦合性能的Sm改性PbTiO₃压电陶瓷。通过引入面网取向密度指数ρ_(hkl)和建立90°电畴转向畴壁平移模型,就改性PbTiO₃陶瓷圆片经不同电压极化后材料内部电畴结构变化作了定量的分析与讨论。结果表明,在改性PbTiO₃陶瓷结构中,90°畴壁空间取向分布具有高度的择优性;极化处理使材料中90°电畴壁显著平移,但其取向分布变化甚少;材料的纵向机电耦合系数K_t与(002)面网取向密度指数增量△ρ₍₀₀₂₎具有基本平行的电场依赖关系。 关键词：     

外加电场对铁电薄膜相变的影响

采用热力学非线性理论,研究了外加电场对立方基底Pb(Zr_0.3Ti_0.7)O₃(PZT)铁电薄膜相变的影响.通过数值计算,得到了"失配应变-外加电场"相图,及外加电场与极化强度的关系.当外加电场达到186 kV/cm时,能使生长在SrTiO₃ 基底上PZT铁电薄膜从单斜r相转变为c相.在实验上,采用扫描探针显微镜通过对PZT薄膜施加不同的极化电场来研究了它的电畴翻转.从得到的压电响应相图可以看出,绝大多数的电畴是清晰可 关键词： 铁电薄膜 相变 扫描探针显微镜 失配应变     

PbTiO3/PbZr0.3Ti0.7O3/PbTiO3夹心结构铁电薄膜子晶层的优化

用Sol-Gel法制备了Pb_(1+x)TiO₃/PbZr_03Ti_07O₃/Pb_(1+x)TiO₃(PT/PZT/PT)夹心结构及PZT铁电薄膜，为了获得高质量的PT/PZT/PT夹心结构铁电薄膜，使用不同过量Pb配比(x)的PbTiO₃ (PT)层进行制备，以获得优化的PT子晶层.X射线     

Au/PZT/BIT/p-Si异质结的制备与性能研究

采用脉冲激光沉积(PLD)工艺,制备了以Bi₄Ti₃O₁₂(BIT)为过渡阻挡层的Au/PZT/BIT/p-Si异质结.研究了BIT铁电层对Pb(Zr_0.52Ti_0.48)O₃(PZT)薄膜晶相结构、铁电及介电性能的影响,对Au/PZT/BIT/p-Si异质结的导电机制进行了讨论.氧气氛530℃淀积的PZT为多晶铁电薄膜,与直接淀积在Si基片上相比,加入BIT铁电层后PZT铁 关键词： 铁电薄膜 异质结构 脉冲激光沉积(PLD)     

(111)取向(Pb,La)TiO3铁电薄膜中90°纳米带状畴与热释电性能的研究

采用射频磁控溅射技术在Pt/Ti/SiO₂/Si(100)衬底上生长了掺镧钛酸铅(PLT)铁电薄膜.用X射线衍射技术(XRD)研究了PLT薄膜结晶性能，结果表明PLT薄膜为 (111)择优取向钙钛矿相织构.使用原子力显微镜(AFM)和压电响应力显微镜(PFM) 分别观察了PLT薄膜的表面形貌和对应区域的电畴结构.PFM观察显示PLT薄膜中存在90°纳米带状畴，电畴的极化为首尾相接的低能量的排列方式，带状畴的宽度为20—60nm.研究了PLT10铁电薄膜的制备条件与性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数ε_r为365、介电损耗tgδ为0.02，热释电系数γ为2.18×10^-8C·(cm²·K)^-1，可以满足制备非制冷红外探测器的需要. 关键词： PLT薄膜 电畴 PFM 极化     

微结构对Eu掺杂Bi4Ti3O12铁电薄膜铁电性能的影响

采用金属有机物分解法在Pt/Ti/Si(111)基底上制备了退火温度分别为600℃,650℃,700℃的Bi_3.15Eu_0.85Ti₃O₁₂(BET)铁电薄膜,并对其结构及铁电性能进行了测试,再使用扫描探针显微镜对BET薄膜的电畴翻转进行了实时观测.BET薄膜c畴发生180°畴变的最小电压为+6V,而r畴由于其高四方性,即使极化电压增至+12V也不会发生翻转.薄膜的铁电性主要源于c畴的极化,随着退火温度的升高,c畴的区域面积增加,BET薄膜的剩余极化强度随之增大.退火温度为700℃的BET薄膜剩余极化强度达到84μC/cm². 关键词： 铁电薄膜 电畴翻转 扫描探针显微镜     

PbTiO3/PbZr0.3Ti0.7O3/PbTiO3夹心结构铁电薄膜子晶层的优化

用Sol-Gel法制备了Pb(1 x)TiO3/PbZr0.3Ti0.7O3/Pb(1 x)TiO3(PT/PZT/PT)夹心结构及PZT铁电薄膜,为了获得高质量的PT/PZT/PT夹心结构铁电薄膜,使用不同过量Pb配比(x)的PbTiO3 (PT)层进行制备,以获得优化的PT子晶层.X射线衍射和原子力显微镜分析结果表明PT层中过量Pb配比(x)对薄膜的微结构影响很大,只有PT层中Pb过量配比x＝0.10-0.15的薄膜为表面晶粒大小均匀致密的纯钙钛矿结构.X射线电子能谱对薄膜微区进行元素成分分析表明,对x=0.00的薄膜,在表面和界面处Pb明显的缺乏;而x=0.20时的薄膜,Pb则明显的过量.薄膜的铁电性能、疲劳特性和漏电流特性等电学性能与PT层中过量Pb配比(x)没有明显的变化趋势,但与薄膜的结晶性能密切相关.结晶性能较好的薄膜,其电学性能也较好.说明PT层中过量Pb配比(x)是通过影响PT子晶层自身的结晶,而影响整个薄膜的结晶行为,并进一步影响到整个薄膜的电学性能.因此,在其他工艺参数都相同时,PT层中合适的过量Pb配比应为x=0.10-0.15.优化的子晶层不仅能获得结晶性能较好的薄膜,而且薄膜的电学性能也好.     

锆钛酸铅薄膜的铁电疲劳微观机理及其耐疲劳性增强

铁电随机存储器(ferroelectric random access memory,FeRAM)因其卓越的数据存储性能与非易失性存储特性等优势而备受关注,但其自身固有的铁电疲劳失效问题制约了 FeRAM进一步的发展和商业化应用.FeRAM的疲劳失效与铁电薄膜的畴壁运动密切相关,但其内在疲劳机理仍有待深入研究.本文采用基于密度泛函理论(density functional theory,DFT)的第一性原理计算方法,研究了锆钛酸铅(Pb(Zr_(0.52)Ti_(0.48))O_3,PZT)的疲劳失效机理并提出了增强其耐疲劳性能的方法.计算结果表明:PZT中氧空位与180°畴壁运动的耦合是其铁电疲劳的内在原因,PZT铁电薄膜中越靠近畴壁的地方越容易形成氧空位,畴壁处大量氧空位对畴壁运动的"钉扎"作用使畴壁迁移困难,抑制了其极化反转最终导致了铁电疲劳;Ba(Mg_(1/)3Nb_(2/3))O_3 (BMN)缓冲层的存在可吸收PZT中的氧空位,降低畴壁处的氧空位浓度,提升其耐疲劳性能.实验结果表明,经过10~(10)次极化反转后,PZT铁电薄膜的剩余极化值降低了 51%,而PZT/BMN薄膜的剩余极化值仅降低了 18%;经过10~(12)次极化反转后,PZT/BMN薄膜的剩余极化值仍保持有82%并持续稳定.以上结果表明,BMN缓冲层引入确实能提高PZT铁电薄膜的耐疲劳性,有望满足FeRAM商业化应用的需求.     

高压退火对0.65PMN-0.35PT薄膜结构、形貌及电学性能的影响

利用射频磁控溅射技术在LaNiO₃/SiO₂/Si(100)基底上制备了厚 度约为250 nm的0.65PMN-0.35PT(PMN-PT)薄膜. 研究高压氧氛围退火方式对PMN-PT薄膜晶体结构、形貌以及电学性能的影响. 经过XRD测试发现,在高压氧气氛围中, 温度为400℃下退火后的PMN-PT薄膜具有纯的钙钛矿相结构, 具有完全的(100)择优取向, 且衍射峰尖锐, 表明经过高压退火后的薄膜结晶极为充分. SEM表面形貌测试结果显示, 经高压退火处理的PMN-PT薄膜表面呈现出棒状或泡状的形貌. 铁电性能测试表明: 氧气氛围压强4 MPa, 退火时间4h的PMN-PT薄膜样品具有较好的铁电性能, 其剩余极化强度P_r达到10.544 μC/cm², 且电滞回线形状较好, 但漏电流较大, 这可能是由于其微结构所导致.同时介电测试发现: PMN-PT薄膜样品具有极好的介电性能, 其在1 kHz下测试的介电常数ε_r达到913, 介电损耗tgδ 较小, 仅为0.065. 关键词： 射频磁控溅射 高压退火 0.65PMN-0.35PT 介电     

Effect of Mn doping defect on 180° domain wall in ferroelectric PbTiO3

The structures, energies, spontaneous polarized properties and charge densities of 180° domain walls with Mn doping at different lattice positions were investigated in ferroelectric PbTiO₃ (PT) using the first-principles calculations. The results show that Mn ion prefers to enter the bulk region rather than the domain wall in terms of energy minimization whether it substitutes for an A-site Pb ion or a B-site Ti ion of PT. In addition the domain wall energy has a minimum value of 124.52 mJ/m² when Mn ion substitutes for Pb ion in the bulk region. And the spontaneous polarization along z axis increasing and the charge density in the domain wall region reducing could be the essential reasons for improving PT's performance after Mn doping at A site.     

Analysis of the magnetic domain structure of electrodeposited nickel studied by neutron depolarization

A polarized monochromatic neutron beam is transmitted through a nickel sheet which has been electrodeposited onto a copper backing. The polarization direction of the incoming beam may be adjusted in three orthogonal directions, while the polarization after transmission through the sample can be analyzed in three independent directions. In this way a (3×3) depolarization matrix can be determined, of which the diagonal elements give the depolarization factors in the successive directions. At zero applied magnetic field and perpendicular transmission no depolarization is observed when the polarization vector is perpendicular to the sheet. The depolarization factors in the other two directions nearly follow a cosine dependence on the neutron wavelength. A structure consisting of domains with magnetization directions perpendicular to the sheet could explain the results. By varying the angle of transmission of the neutron beam with respect to the plane of the sheet one can determine the mean domain size and to some extent the nature of the distribution function of the domain size in the plane of the sheet. In addition, the depolarization has been studied as a function of a magnetic field applied in a direction in the plane of the sheet. The results are compared with magnetization measurements performed in a magnetic field applied in the same direction.     

One-dimensional $\mathcal{PT}$-symmetric acoustic heterostructure

The explorations of parity-time ($\mathcal{PT}$)-symmetric acoustics have resided at the frontier in physics, and the pre-existing accessing of exceptional points typically depends on Fabry-Perot resonances of the coupling interlayer sandwiched between balanced gain and loss components. Nevertheless, the concise $\mathcal{PT}$-symmetric acoustic heterostructure, eliminating extra interactions caused by the interlayer, has not been researched in depth. Here we derive the generalized unitary relation for one-dimensional (1D) $\mathcal{PT}$-symmetric heterostructure of arbitrary complexity, and demonstrate four disparate patterns of anisotropic transmission resonances (ATRs) accompanied by corresponding spontaneous phase transitions. As a special case of ATR, the occasional bidirectional transmission resonance reconsolidates the ATR frequencies that split when waves incident from opposite directions, whose spatial profiles distinguish from a unitary structure. The derived theoretical relation can serve as a predominant signature for the presence of $\mathcal{PT}$ symmetry and $\mathcal{PT}$-symmetry-breaking transition, which may provide substantial support for the development of prototype devices with asymmetric acoustic responses.     

Nonlinear dynamics of a domain wall in the field of a sound wave propagating in the plane of the wall

A theoretical model is proposed for describing the drift of a 180° domain wall in a weak ferromagnet in the field of elastic stresses produced by a strong sound wave propagating in the plane of the wall. The dependence of the drift velocity on the frequency, amplitude, and polarization of the sound wave is found. It is predicted that drift of a striped domain structure is possible.     

Nanoscale domain structures in 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (91PZN-9PT) single crystals studied by piezoresponse forcemicroscopy

High-resolution domain studies have been performed in 91PZN-9PT single crystals by piezoresponse force microscopy. Nanometer- and micron-sized strip-shaped 180º and parallel 90º domains were observed in the rhombohedral (R) and tetragonal (T) phases. Domain patterns with the typical sizes 5–200 nm were observed on the (001)_cub surface of unpoled sample. The existence of nanodomains in the sample is tentatively attributed to the relaxor nature of PZN-PT where small polar clusters may form under zero-field cooling conditions. The domain observation confirms the structure of the morphotropic 91PZN-9PT crystals, which is composed of both the R and T (or monoclinic) orientations states. The outstanding piezoelectric properties may result from the cooperative response of the microscale/nanoscale domain structure.     

The dynamics of domain walls in an easy-plane magnet in the field of an acoustic wave

The drift of a 180° domain wall is studied in an easy-plane weak two-sublattice ferromagnet subject to an elastic-stress field generated by an acoustic wave. The dependences of the drift velocity on the amplitude and polarization of the acoustic wave are found. The conditions of the drift of a stripe domain structure are determined.     

Unusual domain evolution in semiconducting ferroelectrics: A phase field study

The effect of electrical conductivity on the domain evolution of semiconducting ferroelectrics is investigated using a phase field model which includes the drift of space charges. Phase field simulations show that the tail-to-tail 90° charged domain wall appears during the domain formation in the semiconducting ferroelectrics at zero field, which is prohibited in common insulating ferroelectrics. Due to the screening of polarization charges, the domain switching takes place through the motion of head-to-head 180° charged domain wall in the semiconducting single-domain ferroelectrics subjected to an electric field. Comparing to the insulating ferroelectrics, the semiconducting ferroelectrics have a lower speed of domain evolution due to the decrease of mobility of charged domain walls. The response of semiconducting ferroelectrics to a mechanical load is also found different from that of insulating ferroelectrics.     

Structure and dynamic properties of the twisted magnetic domain wall in an electric field

The structure of the domain wall in a magnetically uniaxial ferromagnetic film placed in an external electric field has been studied. It has been shown that the domain wall has a complex twisted structure whose characteristics (thickness, profile, and limit velocity of steady motion) depend on the film thickness, quality factor, and external electric field. The effect of the electric field on the domain wall is caused by inhomogeneous magnetoelectric coupling taking place in domain walls with a twisted structure.