Rochelle salt in an inhomogeneous electric field

The parameters of the hysteresis loop in the ferroelectric Rochelle salt were investigated using a sample with two pairs of electrodes: measurement electrodes and the side ones. It has been shown that the difference between the potentials of the measurement and the side electrodes (generating an inhomogeneous electric field) leads to gradual decay in time t of the remanent polarization P_r. The time required for the hysteresis loop to disappear in the inhomogeneous electric field (not parallel to the ferroelectric axis) decreases with temperature increase from 44±3 h at – 9°C to 2.3±0.1 h at 21.9 °C. On the other hand, the crystal placed for a sufficiently long time simultaneously in the measuring electric field and in the constant inhomogeneous one may finally exhibit a stationary hysteresis loop with a reduced remanent polarization and the unchanged coercive field. It has been shown that the crystal as a whole does not have to be polarized perpendicularly to the ferroelectric axis in order for its hysteresis loop to be reduced.     

Symplectic integration approach for metastable systems

Nonadiabatic behavior of metastable systems modeled by anharmonic Hamiltonians is reproduced by the Fokker-Planck and imaginary time Schr?dinger equation scheme with subsequent symplectic integration. Example solutions capture ergodicity breaking, reassure the H-theorem of global stability [M. Shiino, Phys. Rev. A 36, 2393 (1987)], and reproduce spatially extended response under alternate source fields.     

Application of a ferroelectric plasma cathode as a high-current switch

In this paper the parameters of two types of high-current switches based on ferroelectric BaTiO₃ ignition are presented. Both types of switches showed a reliable and controllable operation with a repetition rate of several Hz. The first type is a vacuum two-electrode switch ignited by the plasma which is generated by a BaTiO₃ cathode. This type of switch was tested in the voltage range of 3-25 kV and switched current amplitude of 2-15 kA with either negative or positive polarity of the high-voltage electrode. The second type is a BaTiO₃ surface flashover strip-like switch ignited by a driving pulse which has an amplitude of several kV. It was shown that the application of the driving pulse (>10 kV) leads to the appearance of many non-complete surface discharges which transform further to a multi-channel discharge. This type of switch was tested in the voltage range of 1-25 kV and current amplitude of 0.5-15 kA. The design of the switches, their lifetime, the time jitter and the parameters of the switched current for different discharge conditions are presented. Received 5 November 2001     

Dynamic hysteresis in ferroelectric systems: experiment and Monte Carlo simulation

A Monte Carlo algorithm for dynamic hysteresis simulation in ferroelectric spin systems is developed based on a DIFFOUR model in which the local spontaneous polarization is defined by the double-well potential energy and the nearest-neighbor spin interaction as well as an external electrical field of variable amplitude and frequency. A direct measurement of the hysteresis loop for ferroelectric Pb(Zr_0.52Ti_0.48)O₃ thin film capacitors using the Sawyer–Tower technique is performed. Significant dependence of the hysteresis shape and pattern on the external field is revealed. Direct imaging of the simulated domain pattern indicates serious suppression of the domain switching over the high-frequency range. The evaluated scaling relations from the simulation for remanence, coercivity, and the area of the hysteresis over the low-frequency range are supported by theoretical predictions and experiments, but the high-frequency scaling behaviors as derived are different from one and another. Received: 23 January 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001     

Second-harmonic imaging of ferroelectric domains in LiNbO3 with micron resolution in lateral and axial directions

Received: 22 May 1998/Revised version: 10 July 1998     

Colored noise in a two-dimensional nonlinear system

A two-dimensional decoupling theory is developed when colored noise is included in a nonlinear dynamical system. By a functional analysis, the colored noise is transformed to an effective noise that includes the noise correlation time, the mean dynamical variable, and the original noise strength. When the two-dimensional decoupling theory is applied to single-mode and two-mode dye laser systems, the mean, variance, and effective eigenvalue of laser intensity are calculated. Excellent agreement between theoretical analysis, numerical simulations, and experimental measurements are obtained. It is seen that the increase of noise correlation time can reduce the fluctuations in the laser system. It is also shown that there is relatively large fluctuation in the phase when the laser undergoes from thermal light to coherent light when the theory is applied to a single mode dye laser. Received 20 August 2001 and Received in final form 4 December 2001     

Investigation of ferroelectric coercive field in LiNbO3

3 using the pulse-field method was performed. It was found that the coercive field varies with time after domain reversal. The possible origins of this phenomenon are discussed. Received: 27 January 1997/Accepted: 7 April 1997     

Formation of the ferroelectric domains in epitaxial PbTiO3 thin films grown by metalorganic chemical vapor deposition

3 thin films have been prepared by metalorganic chemical vapor deposition under reduced pressure. The formation of ferroelectric domains in films grown on SrTiO₃ and LaAlO₃ substrates was investigated by synchrotron radiation and Rutherford backscattering spectroscopy. Single-domain (3000-Å thick) and multi-domain (4500-Å thick) PbTiO₃ films were produced on SrTiO₃. For multi-domain PbTiO₃ film, the c-domain presented epitaxial structure with its c-axis perpendicular to the substrate surface, while a-domains aligned four-fold symmetrically with c-domains by 2.79^° off the c-axis of c-domains. In the film, the measured lattice constants (a, b and c) of the a- and c-domains were different from each other, indicating that the films suffered a modulated strain during domain formation. In contrast, both the a and c domains of films on LaAlO₃ were alternatively aligned on substrate with the a-axis of the a-domain and the c-axis of c-domains perpendicular to the substrate surface. Two-dimensional distribution of these domains is proposed and the formation of these kinds of domains is discussed. The surface morphology and phase transition process of single and multi domain PbTiO₃ film on SrTiO₃ were studied by atomic force microscope (AFM) and high temperature X-ray diffraction, respectively. Received: 15 August 1996/Accepted: 21 January 1997     

Inelastic relaxation and noise temperature in S/N/S junctions

We studied electronic relaxation in long diffusive superconductor/normal metal/superconductor (S/N/S) junctions by means of current noise and transport measurements down to very low temperature (100mK). Samples with normal metal lengths of 4, 10 and 60μm have been investigated. In all samples the shot noise increases very rapidly with the voltage. This is interpreted in terms of enhanced heating of the electron gas confined between the two S/N interfaces. Experimental results are analyzed quantitatively taking into account electron-phonon interaction and heat transfer through the S/N interfaces. Transport measurements reveal that in all samples the two S/N interfaces are connected incoherently, as shown by the reentrance of the resistance at low temperature. The complementarity of noise and transport measurements allows us to show that the energy dependence of the reentrance at low voltage is essentially due to the increasing effective temperature of the quasiparticles in the normal metal. Received 5 February 2002 / Received in final form 6 September 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: hoffmann@drfmc.ceng.cea.fr     

Phase transition and random-field induced domain wall response of SrTi O 3

The dielectric permittivity ε^′ - i of SrTi ¹⁸O ₃ (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε^′ vs. T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results. Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002     

Improvement of metal–ferroelectric–silicon structures without buffer layers between Si and ferroelectric films

Si-based metal–ferroelectric–semiconductor (MFS) structures without buffer layers between Si and ferroelectric films have been developed by depositing SrBi₂Ta₂O₉ (SBT) directly on n-type (100)-oriented Si. Some effective processes are adopted to improve the electrical properties of these MFS structures. Contrary to the conventional MFS structures with top electrodes directly on ferroelectrics, our MFS structures have been developed with thin dense SiO₂ films deposited between ferroelectric films and top electrodes. Due to the SiO₂ films, the leakage current densities of MFS structures are reduced to 2×10^-8 A/cm² under the bias of 5 V. The C-V electrical properties of the MFS structures are greatly improved after annealing at 400 °C in N₂ ambient for 1 h. The C-V memory windows are increased to 3 V, which probably results from the decrease of the interface trap density at the Si/SBT interface. Received: 7 September 1999 / Accepted: 24 November 1999 / Published online: 2 August 2000     

Nonlinear optical and electrostatic force microscopy for ferroelectric polarization imaging

Second-harmonic generation (SHG)-based nonlinear optical microscopy is used for spatially resolved imaging of the polarization switching in lead zirconium titanate ferroelectric thin films. The local SHG hysteresis loops reveal a strong dependence on film composition and structure. The SHG microscopy results are in good agreement with the efficiency of electrostatic force microscopy writing and allow us to predict the microscopic dielectric memory efficiency, both in contact and contact-less ways. Received: 15 January 2001 / Revised version: 27 March 2002 / Published online: 6 June 2002     

Frequency dependence of aging, rejuvenation and memory in a disordered ferroelectric

We characterize in details the aging properties of the ferroelectric phase of KTa_1-xNb_x O₃ (KTN), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c. dielectric susceptiblity scaling as ω, where t _w is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings. Received 10 November 2000 and Received in final form 20 February 2001     

Current and shot noise in two capacitively coupled single electron transistors with an atomic sized spacer

The currents and their fluctuations in two capacitively coupled single electron transistors are determined in the limit of sequential tunnelling. Our considerations are restricted to the case when the islands (dots) of the transistors are atomic-sized, which means each of them has only one single electronic level available for the tunnelling processes. The Coulomb interactions of accumulated charges on the both single electron transistors lead to the effect of the negative differential resistance. An enhancement of the current shot-noise was also found. Spectral decomposition analysis indicated the two main contributions to the shot-noise: low- and high-frequency fluctuations. It was found that the low frequency fluctuations (polarization noise) are responsible for a strong enhancement of the current noise. Received 9 October 2001 / Received in final form 8 March 2002 Published online 9 July 2002     

Fabrication and electrical properties of sol-gel-derived Ba0.8Sr0.2TiO3 ferroelectric films from a 0.05-M spin-on solution

Barium strontium titanate (Ba_0.8Sr_0.2TiO₃) films with good ferroelectricity have been obtained by a developed sol-gel processing, using a 0.05-M spin-on solution. X-ray diffraction and Raman spectroscopy investigations showed that the Ba_0.8Sr_0.2TiO₃ film exhibited a tetragonal structure at room temperature. Field-emission scanning electron microscopy measurements revealed that large columnar grains with the size of 100 to 200 nm in the film were formed from the highly dilute spin-on solution with layer-by-layer homoepitaxy. Electrical measurements for the prepared Ba_0.8Sr_0.2TiO₃ film showed a remnant polarization of 3.5 μC/cm², a coercive field of 53 kV/cm, two distinctive phase transitions, lower dissipation factor, and good insulating properties. These results indicate the sol-gel-derived Ba_0.8Sr_0.2TiO₃ film from a 0.05-M solution is suitable for uncooled infrared detector applications. Received: 19 August 1999 / Accepted: 11 October 1999 / Published online: 1 March 2000     

Switching behaviour of ferroelectric liquid crystals probed by optical second-harmonic generation

Ferroelectric properties of thin (1.5–4 μm planar cells of a ferroelectric liquid crystal (FLC) mixture are studied using electro-optic measurements, second-harmonic generation (SHG) and SHG interferometry. A switching behaviour of the FLC cells in external dc electric fields is observed. It is characterised by rotation of the polarisation plane of the transmitted light and by changes in the SHG intensity, phase and anisotropy dependences, which are attributed to a collective motion of the system as a ferroelectric uniform state with C₂ symmetry. Received: 16 October 2001 / Revised version: 18 March 2002 / Published online: 6 June 2002     

Investigations of structural, dielectric and ferroelectric behavior of europium substituted SrBi2Ta2O9 ferroelectric ceramics

Europium substituted samples of the compositions Sr_1−xEu_xBi₂Ta₂O₉ (x=0.0,0.025,0.050,0.10 and 0.20) were synthesized by solid state reaction method and studied for their structural, dielectric and ferroelectric properties. The X-ray diffractograms confirmed the formation of single phase layered perovskite structure in all the samples. The temperature variation of dielectric constant shows that the Curie temperature (T_c) decreases on increasing concentration of europium. The dielectric loss reduces significantly with europium addition. The P-E studies of the Eu-substituted SBT ceramics show that the remanent polarization increases with increasing concentration of europium.     

Noise correlations in shear flows

We consider the effects of a shear on velocity fluctuations in a flow. The shear gives rise to a transient amplification that not only influences the amplitude of perturbations but also their time correlations. We show that, in the presence of white noise, time correlations of transversal velocity components are exponential and that correlations of the longitudinal components are exponential with an algebraic prefactor. Cross correlations between transversal and downstream components are strongly asymmetric and provide a clear indication of non-normal amplification. We suggest experimental tests of our predictions. Received 26 February 2002 / Received in final form 11 March 2003 Published online 20 June 2003 RID="a" ID="a"e-mail: bruno.eckhardt@physik.uni-marburg.de RID="b" ID="b"Also at: Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India     

Photorefractive detection of antiparallel ferroelectric domains in BaTiO3 and BaTiO3:Co crystals

3 ). Rod-shaped domains with square cross sections are revealed. Received: 11 July 1997/Accepted: 19 November 1997