Internal field and self-polarization in sol–gel-derived lead zirconate titanate films

An internal electric field is induced in a sol–gel-derived lead zirconate titanate (PZT) film of thickness 2 m after the rf-sputtering deposition of the top electrode and this is exhibited as a shift of the P–E loop towards the positive side of the electric field axis. The direction of the internal field is towards the bottom electrode. As the discharge power used for the sputtering decreases, the internal field increases. We suggest that the internal field is induced by the high-energy ion bombardment on the film surface during the rf-sputtering process. Due to the occurrence of the internal field, the as-prepared PZT film becomes self-polarized at a high deposition temperature of 150 °C, thus showing a non-zero pyroelectric coefficient at room temperature. As the internal field increases, the observed pyroelectric coefficient increases and has a large value of 230 C/m²K for an as-prepared PZT film with an internal field of 40 kV/cm. PACS 77.22.Ej; 77.70.+a; 77.90.+k     

Anisotropic polarization response of polar nanostructures in relaxor-type lead lanthanum zirconate titanate ferroelectric ceramics

Polar nanoregions (PNRs) in relaxor-type PLZT ferroelectric ceramics and their response to the out-of-plane, in-plane electric fields were investigated by the high-resolution piezoresponse force microscopy. Anisotropic polarization switching kinetic behaviors of PNRs were found in relaxor PLZT ceramics. Normal, stable ferroelectric domain states were formed through the coalescence of PNRs in the out-of-plane field, while in the high in-plane electric field, the polarization dynamic behaviors of PNRs show spatial inhomogeneity due to the anisotropy random fields in the ferroelectric PLZT ceramics.     

Low-temperature processing of sol–gel-derived lead–zirconate–titanate thin films by oxygen-plasma treatment

Ferroelectric thin films of sol–gel-derived Pb(Zr_x, Ti_1−x)O₃ (lead–zirconate–titanate, PZT) were obtained by the low-temperature processing employing oxygen-plasma treatment. The as-coated PZT films were annealed in oxygen ambience at 450 °C, followed by oxygen-plasma treatment at 200 °C, which gave rise to the ferroelectric hysteresis. Annealing of the as-coated PZT films followed by oxygen-plasma teratment at 200 °C gave rise to the ferroelectric hysteresis.     

The movement of single 90° domain walls of BaTiO3 in an alternating electric field

Single crystals of BaTiO₃, containing one 90° domain wall, were used to study the origin and character of the movement of such a wall in an alternating electric field having a frequency of 50 c/s. The experimental results are discussed from the phenomenological point of view.

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90- BaTiO₃

iO₃, 90- , 50 Hz. .

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The authors would like to thank A. Glanc for preparing the crystals for measurement, V. Dvoák, J. Kaczér and V. Janovec for fruitful discussions.     

Anharmonic lattice statics analysis of 180 ° and 90° ferroelectric domain walls in PbTiO3

This paper presents an anharmonic lattice statics analysis of 180?°?and 90?°?domain walls in tetragonal ferroelectric perovskites. We present all the calculations and numerical examples for the technologically important ferroelectric material PbTiO₃. We use shell potentials that are fitted to quantum mechanics calculations. Our formulation places no restrictions on the range of the interactions. This formulation of lattice statics is inhomogeneous and accounts for the variation of the force constants near defects. The discrete governing equations for perfect domain walls are reduced using symmetry conditions. We solve the linearized discrete governing equations directly using a novel method in the setting of the theory of difference equations. We calculate the fully nonlinear solutions using modified Newton–Raphson iterations.     

Phase evolution studies of sol�Cgel derived lead zirconate titanate (PZT) nanopowder using X-ray diffraction and X-ray photoelectron spectroscopy

We report here the formation of single phase lead zirconate titanate (PZT) nanopowder with composition Pb(Zr_0.52Ti_0.48)O₃ and average crystallite size 12?C20?nm, synthesized by sol?Cgel process. The phase evolution of PZT gel powder, heat treated at temperatures 550, 650 and 800°C was monitored by X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS). The high resolution XPS spectra of Pb4f, Zr3d, Ti2p and O1s show that PZT with pure perovskite structure is obtained at 800°C while at lower temperatures pyrochlore phase co-exists with perovskite phase. The XRD results also support this analysis. We have also identified the pyrochlore phase using XPS by analyzing the corresponding variations in the FWHM values, peak positions and the separation between the spin doublets of Pb, Zr and Ti associated with it. The composition of the final powder obtained with pure perovskite structure is calculated and is close to the designed value.     

In situ neutron diffraction studies of a commercial, soft lead zirconate titanate ceramic: response to electric fields and mechanical stress

Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations. Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis, (002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses.     

Spectra of spin-wave excitations of a 71° domain boundary in a cubic ferromagnet

Features of the long-wavelength part of the spectrum of spin waves localized on a 71° domain boundary of a cubic ferromagnet are examined on the basis of a qualitative analysis and simultaneous numerical solution of the Landau-Lifshitz equations and the equation of magnetostatics. Fiz. Tverd. Tela (St. Petersburg) 41, 2183–2186 (December 1999)     

The inhomogeneity of two-wave coupling in photorefractive crystals in 90° geometry

We derived the coupling equations of two-wave coupling in photorefractive crystals in 90° geometry where pump and signal beams enter two mutually orthogonal crystal faces vertically. We solved the equations numerically in the case of non-local response and illustrated the influence of the coupling coefficient, the absorption coefficient and the ratio of intensities of the two incident beams,R, on the inhomogeneity of transmitted pump and signal beams.     

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.     

Distribution of “structural” elastic stresses in substrate under a thin epitaxial film

A calculation is performed of the structural stresses in a substrate that are due to the mismatching of the lattice parameters of the film and the substrate. By assuming the film to be sufficiently small (h 0.01 p, where p is the distance between the mismatch dislocations), we simplify the initial system of equations for an equilibrium elastic medium, and obtain an exact solution for the parabolic model and an approximate solution for the Peierls-Nabarro model. The analytic and numerical analysis of the solution for the Ge-GaAs system shows that for a depth z 0.05 p the distribution of stresses is not very sensitive to the choice of model and the size of the shear modulus at the separation boundary. Therefore, despite the fact that there are at present no reliable methods for determining , the obtained solution allows us to investigate the distribution of stresses in the depth of a substrate by using a small digital computer.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 77–81, June, 1986.     

Analytical theory for the description of powder systems under compression

In this work, a new theoretical approach to modelling some properties of powder systems under compression is presented. This new theoretical route consists of modelling an actual powder system (with particles of unequal size and irregular form) by means of a system of deforming spheres in a simple cubic arrangement and with a certain global porosity that, in some way, makes it equivalent to the actual one. The study of the evolution of the effective contact area between particles and the effective path of the electric or thermal flow through the powder aggregate is the starting point for establishing the equivalence relationship between the actual system and the simple cubic one. In order to exemplify the utility of this new theoretical tool, two classic problems of practical interest have been studied: the electrical conduction in sintered powders and the law governing the powders’ cold die compaction. The proposed solutions to these problems, as well as the equations allowing one to obtain the equivalence relationship, are validated by experiments carried out in actual powder systems.     

Conduction through 71° domain walls in BiFeO3 thin films

Local conduction at domains and domain walls is investigated in BiFeO(3) thin films containing mostly 71° domain walls. Measurements at room temperature reveal conduction through 71° domain walls. Conduction through domains could also be observed at high enough temperatures. It is found that, despite the lower conductivity of the domains, both are governed by the same mechanisms: in the low voltage regime, electrons trapped at defect states are temperature activated but the current is limited by the ferroelectric surface charges; in the large voltage regime, Schottky emission takes place and the role of oxygen vacancies is that of selectively increasing the Fermi energy at the walls and locally reducing the Schottky barrier. This understanding provides the key to engineering conduction paths in BiFeO(3).     

Antiferroelectric–ferroelectric phase transition in lead zinc niobate modified lead zirconate ceramics: crystal studies, microstructure, thermal and electrical properties

The combination of antiferroelectric PbZrO₃ (PZ) and relaxor ferroelectric Pb(Zn_1/3Nb_2/3)O₃ was prepared via the columbite precursor method. The basic characterizations were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), linear thermal expansion, differential scanning calorimetry (DSC) techniques, dielectric spectroscopy, and hysteresis measurement. The XRD result indicated that the solid solubility limit of the (1−x)PZ–xPZN system was about x=0.40. The crystal structure of (1−x)PZ–xPZN transformed from orthorhombic to rhombohedral symmetry when the concentration of PZN was increased. A ferroelectric intermediate phase began to appear between the paraelectric and antiferroelectric phases of pure PZ, with increasing PZN content. In addition, the temperature range of the ferroelectric phase increased with increasing PZN concentration. The morphotropic phase boundary (MPB) in this system was located close to the composition, x=0.20.     

The motion of 90° wedge domains in BaTiO3 in an alternating electric field

The paper deals with the motion of 90° wedge domains in BaTiO₃ in an alternating field of 50 c/s. The critical field, the positional hysteresis loops with double asymmetry, the production of wedges with polarization perpendicular to the field and 180° substructure in the wedges were studied. The differences between the behaviour of the wedges and the individual 90° walls are pointed out which are caused by differences in the energy balance of these formations and by different interactions with 180° processes. The upper limit of contribution of the wedge motion to the initial permittivity is estimated. The results are discussed from the phenomenological point of view.

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90° BaTiO₃

90° BaTiO₃ , 50 Hz. , , , , , , 180° . 90° , 180° . , . .

     

Anomalous behavior and phase transformation of α-GaOOH nanocrystals under static compression

The structural compression mechanism and compressibility of gallium oxyhydroxide, α-GaOOH, are investigated by in situ synchrotron radiation x-ray diffraction at pressures up to 31.0 GPa by using the diamond anvil cell technique. Theα-GaOOH sustains its orthorhombic structure when the pressure is lower than 23.8 GPa. The compression is anisotropic under hydrostatic conditions, with the a-axis being most compressible. The compression proceeds mainly by shrinkage of the void channels formed by the coordination GaO_3(OH)_3 octahedra of the crystal structure. Anomaly is found in the compression behavior to occur at 14.6GPa, which is concomitant with the equatorial distortion of the GaO_3(OH)_3 octahedra. A kink occurs at 14.6 GPa in the plot of finite strain f versus normalized stress F, indicating the change in the bulk compression behavior. The fittings of a second order Birch–Murnaghan equation of state to the P–V data in different pressure ranges result in the bulk moduli B_0= 199(1) GPa for P 14.6 GPa and B_0= 167(2) GPa for P 14.6 GPa. As the pressure is increased to about 25.8 GPa, a first-order phase transformation takes place, which is evidenced by the abrupt decrease in the unit cell volume and b and c lattice parameters.     

Waveguide Bend of 90° in Two-Dimensional Triangular Lattice Silicon Photonic Crystal Slabs

We design and realize a 90° waveguide bend in two-dimensional triangular lattice silicon photomc crystal slabs by connecting linear waveguides along the orthogonal Г - K and Г - M directions. A pass band of 70hm is realized by optimizing the geometry of the Г - M waveguide. The connection region of the waveguide bend is optimized to improve the transmission efficiency of infrared light through the two different kinds of waveguides. The transmission efficiency of an optimized single bend is about 75% in simulation and 45% in measurement.     

Propagation of Lamb waves in pure longitudinal modes

I.IntroductionSinceLambwaveshavewideaPplicationinnondestructiveinspectionandsensors1interestsintheinvestigationofit8propagationaredeveloped.VictorovI1lhaspointedoutthatastohomogeneous,whformsolidplateinunersedillliquld,theverticaldisplacementoftheplate'ssurfaCemaybezerowhenthephasevelocityisequaltotheplatelongitudinalwavespeed.ThisconclusionhasimportantaPplication.RecelltlyPilaskietc.I2]aPproveditbyusing.thefree-boundaryLambwavtheoryandgavetheconditionstoreachit.ItisknownthatthedisaPpeara…     

A contribution to the statics of 90° wedge-shaped domains in BaTiO3 crystals

The existence of 90? domains of wedge and parallelepiped shape was studied in BaTiO₃ crystals of different form. On the basis of a simple model the condition for their origin is discussed.