Effect of electrodes on the properties of a thin ferroelectric film

The effect of various metal electrodes on the properties of thin ferroelectric films is considered using the phenomenological Ginzburg-Landau theory. The electric field produced by charges on electrodes is taken into account (with allowance for the screening of the charges in the metals) in the free energy functional and in the Euler-Lagrange equation for the film polarization. This equation is solved using the variational method, and the free energy functional is reduced to the conventional free energy with a renormalized coefficient of P ². This coefficient is dependent on the properties and thickness of the film and the properties of the electrode. Therefore, the physical characteristics of the size effect can be found by merely substituting the renormalized coefficient into the usual formulas from phenomenological theory. The calculations are shown to be in good agreement with the experimental data for Pt, Ir, IrO₂, and SrRuO₃.     

Epitaxial growth of ferroelectric PLZT thin film and their optical properties

A series of experiments for growing epitaxial PLZT thin films has been made with rf sputtering. X-ray and electron diffraction analyses confirm that the fabricated films grow epitaxially on SrTiO₃ and MgO crystals. A good transparency in the region above 0.4 μm to infrared with good ferroelectric properties is obtained. Propagation loss of He−Ne laser light is less than 6 dB/cm, and the PLZT thin film is a promising candidate for the optical modulator and other functional elements for integrated optics.     

Theoretical studies on the pyroelectric properties of two component composite ferroelectric thin film

Using a Ginzburg–Landau–Devonshire type model, the pyroelectric property and hysteresis loop are studied for a composite ferroelectric thin film that contains an insertion of a different type of ferroelectric material in parallel connection with the host ferroelectric film material. If these two types of ferroelectric materials are polarized along the same direction, there are two peaks occur in the pyroelectric coefficient vs temperature curve. If the two ferroelectric materials are polarized in opposite directions, one positive and one negative coefficient peaks occur in the temperature dependence of pyroelectric coefficient curve and the hysteresis loop appears to be a quasi-double loop. The effect of the external electric field on the pyroelectric coefficient is also investigated.     

Enhancement of dielectric and ferroelectric properties in ferroelectric superlattices

I studied theoretically the enhancement of remanent polarization and dielectric permittivity of interfacial-coupled ferroelectric superlattices based on the Landau–Ginzburg theory. Our model adopts the Landau–Khalatnikov equation to describe hysteresis behavior and takes the time-dependent space-charge-limited conductivity into account to investigate the ferroelectric and dielectric properties of ferroelectric superlattices. The results are in good agreement with recent experimental observations on the enhancement of remanent polarization and permittivity of BaTiO₃/SrTiO₃ superlattices and heterolayered Pb(Zr,Ti)O₃ thin films.     

Investigation of the crossover properties for the interaction parameters of a ferroelectric thin film

The crossover feature, from the ferroelectric-dominant phase diagram (FPD) to the paraelectric-dominant phase diagram (PPD), for the interaction parameters of a ferroelectric thin film described by the transverse Ising model have been calculated in detail by the use of the mean-field approximation. The crossover values of the exchange interactions and the transverse fields for a thin film with certain layers are displayed as a curved surface in the three-dimensional parameter space. The numerical results show that for thin films with different numbers of layers there exists a common intersection line for the curved surfaces of the crossover values. Meanwhile the layer-independent equation for the intersection line is obtained for the first time.     

Dielectric properties of film materials based on polyethylene terephthalate and polycarbonate with ferroelectric inclusions

The dielectric properties of film materials based on polyethylene terephthalate and polycarbonate with inclusions of triglycine sulfate (TGS) and TGS with admixture of L, ??-alanine (ATGS) have been studied. An increase in the temperature of the phase transition in these materials as compared to in bulk TGS and ATGS has been revealed.     

Charge contrast of ferroelectric domain walls in ferroelastic terbium molybdate

An extraordinary potential contrast of a plane domain wall forming in the case of excess negative charging of a ferroelastic-ferroelectric Tb₂(MoO₄)₃ sample with a two-domain structure has been detected using a scanning electron microscope. Conditions and features of the formation of this potential contrast (called charge contrast) in the domain wall region are determined. It is shown that the surface is charged at a lower rate in the domain wall region, which is an elastically strained crystal region. The smallest domain wall width determined by the charge-contrast image was 1.6 μm on the average.     

Efficiency of thermoelectric conversion in ferroelectric film capacitive structures

Thermal heating/cooling conditions for metal-insulator-metal structures based on barium strontium titanate ferroelectric films are studied by numerical methods with the aim of their application in capacitive thermoelectric converters. A correlation between the thermal and capacitive properties of thin-film ferroelectric capacitors is considered. The time of the temperature response and the rate of variation of the capacitive properties of the metal-insulator-metal structures are determined by analyzing the dynamics of thermal processes. Thermophysical calculations are carried out that take into consideration the real electrical properties of barium strontium titanate ferroelectric films and allow estimation of thermal modulation parameters and the efficiency of capacitive thermoelectric converters on their basis.     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO2/Si衬底上制备出Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜,研究了La掺杂对Bi4Ti3O12薄膜的晶体结构、铁电性能和疲劳特性的影响,发现La掺杂没有改变Bi4Ti3O12薄膜的基本晶体结构,并且提高了Bi4Ti3O12铁电薄膜的剩余极化值和抗疲劳性能,对La掺杂改善Bi4Ti3O12铁电薄膜性能的机理进行了讨论.     

Deformation of a ferroelectric smectic film in an electric field

Mechanisms of static deformation of a freely suspended ferroelectric smectic (C*) film in an external transverse electric field are analyzed. An equation for the shape of the film that includes the interaction of the applied field with the polarization vector and surface charges is derived in terms of the variational approach. The effect of deformation is shown to be of threshold character, which agrees with the experimental data.     

Phase diagram of ferroelectric thin film with diluted surface

We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter q$q$ that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter q$q$. The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed.     

Transport properties of a ferroelectric tunnel junction in bilayer ferroelectric/manganite structures

This paper presents the results of an experimental investigation of current flow through a ferroelectric nanolayer in a series of bilayer ferroelectric/manganite structures prepared by metalorganic aerosol deposition on a MgO substrate. It has been shown that a variation in the thickness of the ferroelectric layer in a bilayer ferroelectric/manganite structure leads to a change in the metal-insulator phase transition temperature of the manganite layer and also affects the transport properties of the ferroelectric/manganite structure. Based on the analysis of the experimental results, it is demonstrated that the ferroelectric layer up to 4 nm thick exhibits polarization properties. In the theoretical analysis, it is assumed that electrical conduction of bilayer structures is provided by a dual mechanism combining the electron tunneling through a ferroelectric barrier and the ohmic current flow in a manganite layer. The possibility of retaining the mechanism of charge carrier tunneling in a bilayer ferroelectric/manganite structure through the ferroelectric layer up to 6 nm thick is discussed.     

Thermal properties of PZT-based ferroelectric ceramics

The thermal properties of piezoelectric ceramics (PKR-8, PKR-7M) based on lead zirconate titanate solid solutions Pb(Ti, Zr)O₃ were studied over the temperature range 300–800 K. The thermal conductivity and thermal expansion coefficients were found to exhibit an anomalous behavior in the region of the ferroelectric phase transition.     

Dielectric properties of ferroelectric diisopropylammonium iodide

Temperature dependences of dielectric constant, amplitude of the third harmonic and heat capacity for the organic ferroelectric of diisopropylammonium iodide (C₆H₁₆NI) have been investigated. The measurements were carried out through heating and cooling cycles in the range of 300–400?K. It was found that upon the first heating, only one phase transition occurred without the presence of the ferroelectric phase. For samples preheated over 420?K, two phase transitions at 363 and 378?K appeared in the heating process, and the ferroelectric state was also observed between them. Upon cooling, the ferroelectric phase was detected in the range of lower 361?K and persisted up to room temperature.     

Secondary ferroic properties of ferroelectric crystals

Twenty five types of structural phase transitions that are accompanied by the appearance of a spontaneous optical activity in the low-temperature phase are analyzed. A technique is proposed for describing the enantiomorphic domain structure (orientation states) in these crystals.     

Analysis of polarization switching in ferroelectric crystals in the injection mode

We report on the results of experiments on polarization switching in a ferroelectric TGS crystal during injection of electron beams from a scanning electron microscope under a surface layer. A series of models reflecting the polarization switching dynamics of a ferroelectric crystal under the action of an injected charge is constructed. The implementation of these models is based on the principles of evolution of domain structures taking into account analysis of possible polarization switching mechanisms for ferroelectric samples. A mathematical model developed using these principles demonstrates qualitative similarity of model current pulses and those obtained experimentally in the injection mode.     

可调谐超导滤波器技术的研究

通过研究可调谐滤波器的基本原理,利用钛酸锶铁电薄膜介电常数随外加电场变化的特性,以铝酸镧为基片,采用多层薄膜和三次套刻两种方法设计出可调谐超导滤波器,通过外加电压实现滤波器频率的调谐。     

Depolarizing a ferroelectric film by ac fields of diminishing amplitude

In this paper, we demonstrate that a sol-gel-derived lead zirconate titanate film can be depolarized by the application of ac fields of diminishing amplitude, and we explain the phenomenon based on the concept of the Preisach model. The amplitude of the ac fields is decreased from 19.5 MV/m to 0.2 MV/m in eight steps. The observed piezoelectric coefficient of the film decreases after each step and finishes with almost the same value as that of an as-deposited film. Our results also reveal the existence of a distribution of coercive fields in the microdomains (Preisach dipolar units), and that the P–E loop of each microdomain is shifted by interaction fields so that the magnitudes of its switch-up and switch-down fields are not necessarily the same. PACS 77.22.Ej; 77.70.+a; 77.90.+k     

The polarization and dielectric susceptibility of a ferroelectric bilayer film

A ferroelectric bilayer film consisting of two different ferroelectric constituent films with a transition layer within each constituent film and interfacial coupling between two materials is investigated based on the Ginzburg-Landau-Devonshire phenomenological theory. A parameter α, which describing the differences between physical properties of two constituent films is first introduced in our paper, and reflects a more realistic situation compared to the previous treatments assuming the same two constituent films. We study the polarization and dielectric susceptibility properties of the ferroelectric bilayer film with two different constituent films. The results present some interesting phenomena due to the introduction of parameter α.