Crystallographic study of the rhombohedral-oriented domains in a La0.7Sr0.3MnO3 film

The microstructures present in a thin film of La_0.7Sr_0.3MnO₃, grown by computer-controlled laser molecular beam epitaxy on a SrTiO₃ (001) substrate, were characterized by means of cross-section and plan-view transmission electron microscopy. Four kinds of rhombohedral-oriented domains and two types of domain boundaries were identified in the film. The crystallographic relationships between each domain and the substrate were established on the basis of a hexagonal unit cell using Miller–Bravais indices. A mechanism for the formation of the oriented domains is proposed from the viewpoint of the evolution of strain relaxation during film preparation.     

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     

Transmission electron microscopy investigation of domains and boundaries in bulk La2/3Ca1/3MnO3

The microstructure of domains and boundaries in a bulk orthorhombic La_2/3Ca_1/3MnO₃ material is analysed by applying symmetry group theory. Group theory predicts that the 120° and 90° orientation domains occur in bulk La_{1? x} Ca _x MnO₃ (LCMO) when the cubic LCMO transforms into the orthorhombic LCMO by means of a structural phase transition. The orientation domains are observed and characterized by means of electron diffraction and high-resolution electron microscopy. Antiphase boundaries due to the loss of translation operations have displacement vectors of 1/2[010]o, 1/2[101]o and 1/2[111]0, according to the group theory. Diffraction contrast technique reveals that the displacive vector of most antiphase boundaries is 1/2[111]o, which is also confirmed by means of high-resolution electron microscopy.     

La0.3Sr0.7TiO3模板层对Pb(Zr0.5Ti0.5)O3薄膜的铁电性能增强效应的研究

通过sol-gel法在Si (111) 基片上分别制备了LaNiO₃(LNO)底电极和LaNiO₃/La_0.3Sr_0.7TiO₃ (LNO/LSTO)底电极.然后采用sol-gel 方法，在两种衬底上分别制备了Pb (Zr_0.5Ti_0.5)O₃ (PZT)铁电薄膜.XRD分析表明，两种PZT薄膜均具有钙钛矿结构，且在LNO底电极上的PZT薄膜呈(100) 择优取向，而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明，相对LNO衬底上制备的PZT薄膜，在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强，同时矫顽场也增大.介电常数和漏电流的测试表明，LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流. 关键词： PZT薄膜 铁电性 漏电流 0.3Sr_0.7TiO₃')" href="#">La_0.3Sr_0.7TiO₃     

Characterization of 90° domain structure and polarization switching in Pb(Zr0.4Ti0.6)O3 film by piezoresponse force microscope

A lead zirconate titanate Pb(Zr_0.4Ti_0.6)O₃ (PZT40/60) film was deposited on a Pt(111)/Ti/SiO₂/Si(100) substrate by a sol–gel process followed by thermal annealing at 650 °C for 5 min. Piezoresponse force microscope observation revealed a lamellar domain structure in the PZT40/60 grains and we attribute the lamellar domains as 90° ferroelectric domains. The polarization-switching mechanism of the 90° domains in the PZT40/60 film under external electric fields has also been studied and it was revealed that a large-area polarization switching is usually accompanied by the appearance of a new direction of 90° domains in order to reduce the stress in the grains. By contrast, a nanometer-sized polarization switching is believed to be accomplished by generating 180° domains within a single lamellar domain. PACS 77.80.-e; 77.84.-s; 68.55.-a; 68.37.-d     

Etching of slip produced antiphase domain boundaries in iron-silicon alloys

A method for revealing the slip produced antiphase domain boundaries in nearly stoichiometric ordered Fe₃Si alloys by chemical etching in a solution of HF + H₂O₂ + H₂O is reported. The method was applied to determine the character of superlattice dislocations in strained crystals. Perfect superlattice dislocations were found at the beginning of deformation. Imperfect superlattice dislocations producing antiphase domain boundaries were found at higher deformations.     

Monte Carlo simulation of antiphase boundaries and growth of antiphase domains in Al5Ti3 phase in Al-rich γ-TiAl intermetallics

Predominantly two kinds of antiphase boundaries (APBs) form in Al₅Ti₃, which is an Al-rich ordered derivative of the γ-TiAl (L1₀) phase. This phase can be viewed as a periodic arrangement of lean rhombs and squares on the Ti-rich (002) planes of the tetragonal L1₀. Energies of the two types of APBs were varied in a Monte Carlo simulation by suitably changing the pair interaction parameters. APBs of both types form boundaries of Al₅Ti₃ antiphase domains (APDs), which coarsen with time. An important observation in this regard is that mostly facetted APBs form at lower ageing temperatures, whereas curved APBs appear to form at relatively higher ageing temperatures. The findings of this work suggest that there exists a critical temperature, akin to the roughening transition temperature for crystals, that marks the transition from facetted to curved APBs.     

Microstructure and polarity of epitaxial ZnO films grown on LSAT(111) substrate studied by transmission electron microscopy

Transmission electron microscopy is used to investigate the structural characteristics of epitaxial ZnO thin films grown on (LaAlO₃)_0.3(Sr_0.5Ta_0.5O₃)_0.7(111) (LSAT) by rf plasma-assisted molecular beam epitaxy. It is found that the growth temperature plays a key role in the formation of microstructures in ZnO film. Growth temperature dependence of rotation domain, interface and dislocation structures is studied, and the mechanism for polarity selection is discussed.     

Magnetic behavior and role of the antiphase boundaries in Fe3O4 epitaxial films sputtered on MgO (001)

Magnetite Fe₃O₄ films were grown on single crystal MgO (001) substrates using facing target sputtering technique. Conversion Electron M?ssbauer Spectroscopy and magneto optical polar Kerr spectra have confirmed the stoichiometric repartition of Fe cations corresponding to the inverse spinel structure and the electronic structure characteristic of bulk Fe₃O₄. Hysteresis loops carried out at room temperature show that, in a 1 T applied magnetic field, only 60% of the saturation magnetization is detected. This behavior is discussed in correlation to the antiphase boundaries (APBs) observed by electron microscopy. Magnetic force microscopy studies show that magnetic domains are larger than the mean distance between APBs. Received 2 July 2001     

Structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7−δ films on vicinal substrates

A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa₂Cu₃O_7?δ films on vicinal SrTiO₃ substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa₂Cu₃O_7?δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films.     

Growth and interfacial properties of atomic layer deposited Al0.7Ti0.3O y high-k dielectric on Ge substrate

Growth and interfacial properties of atomic layer deposited Al_0.7Ti_0.3O _y on Ge have been investigated as a potential high-k gate dielectric for future Ge-based metal oxide semiconductor devices. A sandwich structure of Al₂O₃/TiO₂ stack is proposed for Al₂O₃/TiO₂ intermixing and high-k/Ge interfacial passivation. The film thicknesses and interface microstructure are characterized by spectroscopy ellipsometry and high-resolution transmission electron microscopy. X-ray photoelectron spectrometry is used to analyze the chemical composition and bonding states, and to reveal the band alignment of high-k/Ge heterojunctions. Metal-oxide-capacitors are formed by depositing aluminum electrodes to perform capacitance–voltage measurements for electrical characteristics. All evidences show a positive prospect of employing atomic layer deposited Al_0.7Ti_0.3O _y as high-k gate dielectric for future Ge-based devices.     

Improved electrical properties in La- and V-co-doped Na0.5Bi4.5Ti4O15 thin films

Ferroelectric La- and V-co-doped Na_0.5Bi_4.5Ti₄O₁₅ (NLBTV) thin film was prepared on Pt(111)/Ti/SiO₂/Si substrates by using a chemical solution deposition method and annealed at 750?°C under oxygen atmosphere. Crystal structure of the thin film was investigated by X-ray diffraction and Raman scattering. Surface morphology of the thin film was investigated by scanning electron microscopy. The NLBTV thin film capacitor exhibited better ferroelectric properties such as larger remnant polarization and smaller coercive electric field than Na_0.5Bi_4.5Ti₄O₁₅ (NBT) thin film capacitor. Reduced leakage current was observed in the NLBTV thin film capacitor compared to the NBT thin film capacitor. Almost no polarization fatigue was observed up to 1.44×10¹⁰ switching cycles.     

Electrical studies on Zr-modified Bi3.25La0.75Ti3O12: a promising FRAM ceramic

Zr-modified Auruvillius family of lanthanum bismuth titanate, namely Bi_3.25La_0.75Ti_3?xZr_xO₁₂ (BLTZ, x = 0, 0.1, 0.3, 0.5, 0.7 and 1), was prepared by solid-state reaction method. Dielectric properties of the ceramics were studied as a function of temperature. Hysteresis measurements were also performed. Among the composition, Bi_3.25La_0.75Ti_2.9Zr_0.1O₁₂ (BLTZ1) showed large remnant polarization compared to the promising ceramic, namely Bi_3.25La_0.75Ti₃O₁₂. The results were corroborated with the pyroelectric, electric polarization and Raman spectroscopic data.     

Superdomain structure and high conductivity at the vertices in the (111)-oriented epitaxial tetragonal Pb(Zr,Ti)O3 thin film

Recently, in ferroelectric materials, there have been many experimental efforts to find out more intriguing topological objects and their functionalities, such as conduction property. Here we investigated ferroelectric domain structures and related topological defects in the (111)-oriented epitaxial tetragonal PbZr_0.35Ti_0.65O₃ thin film. Systematic piezoresponse force microscopy measurements revealed that the field-induced polarization switching can form thermodynamically stable superdomain structures composed of nano-sized stripe subdomains. Within such superdomain structures, we observed the exotic equilateral triangular in-plane flux-closure domains composed of three stripe domain bundles with 120/120/120 degrees of separation. The conductive-atomic force microscopy measurements under vacuum showed that some vertices have significantly higher conductivity compared to other surrounding regions. This work highlights electric field-driven polarization switching and unique crystallographic symmetry (here, three-fold rotational symmetry) can generate exotic ferroelectric domain structures and functional topological defects, such as conductive vertices.     

Piezoelectric activities and domain patterns of orthorhombic Ba(Zr,Ti)O3 ceramics

Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were prepared by conventional solid-state reaction method. Crystalline structures were analyzed by X-ray diffraction. It was shown that all the Ba(Zr_xTi_1?x)O₃ (0.025 ≤ x ≤ 0.065) ceramics were of orthorhombic phase at room temperature. Piezoelectric activities and domain patterns were investigated and compared with those of BaTiO₃ ceramic. All the Ba(Zr_xTi_1?x)O₃ ceramics showed nearly the same d₃₃ values of about 265 pC/N and the same domain width of about 220 nm. By comparing the grain sizes and domain width of the Ba(Zr_xTi_1?x)O₃ ceramics with those of BaTiO₃ ceramic, it is speculated that the variation of domain width with grain sizes in orthorhombic Ba(Zr_xTi_1?x)O₃ ceramics may be different with that in tetragonal BaTiO₃ ceramic. Besides domain width, the effective inertia mass of domain wall is also considered to be a very important factor that impacts the piezoelectric activities of the Ba(Zr_xTi_1?x)O₃ ceramics.     

Investigation of domain behaviour in 0.7Pb(Mg1/3Nb2/3) O3-0.3PbTiO3 single crystals at different temperatures in the transmission electron microscope

Using transmission electron microscopy, in-situ changes in ferroelastic domains in 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystals were observed at 60 to -163°C. At -163°C, the microscopic tweed morphology of the ferroelastic domains rotated by 90°, and certain orientation changes in the mesoscopic sawtooth domains took place. At this temperature, the ferroelastic domains became coarsened and certain S-shaped mesoscopic domains were reshaped. The disappearance and/or changes in the orientations of both the sawtooth and the ferroelastic domains were reversible upon return to room temperature. On heating to 60°C, both the mesoscopic sawtooth and the microscopic tweed domains were stable below 53°C. Above 53°C, the mesoscopic walls disappeared and the contrast of the tweed domains became blurred. Upon return to room temperature from 60°C, the mesoscopic domain patterns could not be retrieved, indicating that the transformation was irreversible. The morphology of the tweeds at this temperature indicated a structural transition from a two-variant domain state to a multivariant state, eliminating mesoscopic boundaries.     

Dielectric response of PVC polymer loaded with Ba0.3Na0.7Ti0.3Nb0.7O3 ceramic powder

Dielectric response of poly(vinyl chloride), (PVC), loaded with different amount of Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ (BNTN) ceramic powders was investigated in frequency range 100 Hz–1 MHz and temperature range 100–450 K. Ceramic solid solution of barium titanate and sodium niobate with composition Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ was obtained from BaCO₃, TiO₂, Na₂CO₃ and Nb₂O₅ by conventional method. Powders were prepared by grinding of ceramics. The obtained ceramics, used to produce BNTN–PVC composites, are characterized by the relaxor behaviour with a broad peak of dielectric permittivity ε′ at T _m ≈ 230 K. The microstructure of the powders was observed and the grain size was estimated using scanning electron microscope Hitachi S-4700. The EDS analysis confirms the qualitative and quantitative chemical composition of powders and ceramics. The BNTN–PVC composite samples of 0-3 connectivity were prepared from ceramic and polymer powders by hot-pressing method. The dielectric response of the composites displays features originated from the PVC polymer modified by those of BNTN ceramics. The relaxation time of the α-process of PVC obeys the Vogel–Fulcher law and decreases with increasing volume fraction of the ceramics.     

Mechanism of grain-boundary magnetoresistance in Fe O films

The magnetotransport properties of magnetite films with different microstructures were investigated in order to identify prerequisites for the attainment of a large tunnelling magnetoresistance in polycrystalline samples. Epitaxial films on MgAl₂O₄, polycrystalline films on Al₂O₃ and rough MgAl₂O₄ substrates and a polycrystalline La_0.7Ca_0.3MnO₃ film on MgO were compared. Although grain boundaries induce a large high-field magnetoresistance in magnetite films, the low-field magnetoresistance characteristic for spin-polarized tunnelling was virtually absent in these samples. Two factors might be responsible for this behaviour: (1) grain boundaries in magnetite are conducting and do not form tunnelling barriers and (2) the spin-polarization near grain boundaries is suppressed due to non-stoichiometry. Received 15 April 2002 Published online 13 August 2002     

Effects of substitutional impurity Au and Si atoms on antiphase boundary energies in Ti3Al: A first principles study

Effects of substitutional impurity atoms Au and Si on the energies of antiphase boundaries (APBs) on {1100} and (0001) planes in a Ti₃Al intermetallic compound were examined using first principles calculations. Au additions reduce the energies of APBs on both {1100} and (0001) planes by up to more than 40%. The reduction tends to be more remarkable especially when the added Au atom has larger number of Al atoms on its second-nearest neighbor sites rather than on first-nearest neighbor ones. In addition, in the case of Si addition, a significant energy reduction was found only for APBs on (0001) planes, and no remarkable dependence of APB energies on the coordinating atoms was found even for APBs on (0001) planes. These results are crucial to both understanding of the effect of APBs on the impurity diffusivity and predicting the ability of impurity atoms to stabilize antiphase domain structure that increases the strength of Ti₃Al dramatically.     

High-frequency excitations of stripe-domain lattices in magnetic garnet films

Magnetic garnet films of composition (Y,Bi)₃(Fe,Al)₅O₁₂ have been grown by liquid phase epitaxy on [111] and [110] oriented substrates of gadolinium gallium garnet. The domain wall resonance and the two branches of the domain resonance of periodic stripe domains are measured as function of the bias induction applied in the film plane parallel to the stripes. Resonance frequencies up to 7.5 GHz are observed. An improved version of the hybridization model is developed to describe these resonances. It turns out that hybridization of the domain resonance branches is determined by the cubic anisotropy for [111] oriented films, while for [110] oriented films coupling of the domain resonances is mainly caused by the orthorhombic anisotropy. The theoretical model is in excellent agreement with experiments, no fitting parameters are used. It is also used to derive the phase relation between the precessing magnetizations of neighbouring domains.