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A comparison of the available concepts on the effect of spontaneous polarization on the height of the Schottky barrier at the metal-ferroelectric contact with the corresponding experimental data has been used as a basis for setting up an alternative model of this phenomenon, which draws on the dependence of the electron work function of a ferroelectric on the magnitude and orientation of the spontaneous polarization vector.

It has been shown that the phase transitions observed at temperatures of about 250 K in crystals of protein amino acids and of their compounds grown from water solutions are related to drops of these solutions trapped by crystals in their growth.

Processes of the polarization switching in ceramic relaxors Pb(Mg1/3Ti1/3W1/3)O3, Pb(Mg1/4Sc1/4Nb1/4W1/4)O3, Pb(Mg1/5Sc1/5Ti1/5Nb1/5W1/5)O3, and Pb(Mg1/6Sc1/6Ti1/6Sn1/6Ta1/6W1/6)O3 have been investigated at frequencies from 50 Hz to 2 kHz in the temperature range 90–300 K for measuring field amplitudes up to 20 kV/cm. It has been demonstrated that, under specific conditions, these materials are characterized by saturated dielectric hysteresis loops, which indicate the appearance of the ferroelectric state induced by the electric field. The dependences of the spontaneous polarization and the coercive field of the relaxors under investigation on their chemical composition, temperature, and frequency of the measuring voltage have been determined.

The paper reports on the conditions of, and the mechanisms involved in pretreatment by strong electric field (“forming”) and subsequent resistive switching in Au/TiO 2 /Pt thin film structures on silicon. The thin TiO 2 films in these structures were prepared by different methods, namely, vacuum evaporation of metallic titanium followed by its thermal oxidation in air, and RF cathode sputtering of titanium dioxide from a powder target. Current-voltage and voltage-capacitance characteristics of the structures, as well as the relations connecting their conductivity with hold time under dc voltage of different polarities and temperature have been measured. The data obtained permit a conclusion that the physical mechanism underlying the forming consists in a sharp increase of the density of surface states in TiO 2 films initiated by electric breakdown of the Schottky barrier at the contact with the platinum electrode, while the resistive switching of the structures is governed by the variation of the occupati...

This paper reports on a study of the dielectric properties of DNA (sodium salt from calf thymus, SIGMA) under heating and cooling of a sample within the temperature interval 20–60°C, which was conducted in air, in a humid environment, and in vacuum. It is shown that the data obtained can be accounted for by the sample conductivity increasing as a result of DNA releasing water into a separate phase with increasing temperature and the formation of a double electric layer at the DNA interface with metallic electrodes, without invoking the idea of ferroelectricity present in DNA.

The conditions and physical mechanisms of electroforming and subsequent resistive switching in Au/TiO2/Pt thin film structures were investigated. It was concluded that the electroforming, being a current-limited electric breakdown of the TiO2 films, resulted in a considerable increase of the oxygen vacancy concentration in the bulk and on the surface of the films. The resistive switching implemented by short voltage pulses of different polarities is proposed to be due to the change of the Schottky barrier height at the Pt/TiO2 interface as a result of the current-induced variation of the occupancy by electrons of the surface states in the band gap of TiO2.

The conditions and mechanisms of preliminary treatment in strong electric fields (forming) and subsequent resistive switching in Au/TiO2/Pt thin-film structures on silicon were investigated. The thin TiO2 films in these structures were prepared by different methods, namely, vacuum evaporation of metallic titanium followed by thermal oxidation in air and radio-frequency cathode sputtering of titanium dioxide from a powder target. The current-voltage and voltage-capacitance characteristics of the structures, as well as the dependences of their conductivity on the time of exposure to a dc voltage of different polarities and on the temperature were measured. The data obtained permitted the conclusion that the physical mechanism underlying the forming process consists in a sharp increase in the density of surface states in TiO2 films due to the electric breakdown of the Schottky barrier at the contact with the platinum electrode, whereas the resistive switching of the structures is governed by the variation in the population of surface states in the TiO2 band gap and/or in the defect concentration in the barrier region of the structures acted upon by voltage pulses of different polarities.

A number of novel protein amino acid-based single crystals were grown from aqueous solutions and their dielectric and pyroelectric properties were studied in a temperature range 140–340 K. It was shown that some of the crystals such as L-His· (H3P04)2, L-Tyr· HCl, L-Ala2H3PO3· H2O have pyroelectric figure-of-merit comparable to those of TGS. Anomalous dielectric properties of DL-Ser2· H2S04· H2O single crystals were observed in a temperature range 260-270 K revealing a first-order phase transition to an incommensurate phase.

The temperature dependences of the real and imaginary parts of the complex permittivity of diserine sulfate monohydrate crystals and of their electrical response in different crystallographic directions to a change in temperature are investigated. It is confirmed that these crystals undergo a first-order phase transition in the temperature range 260–270 K. This phase transition is assumed to originate from the freezing of the orientational degrees of freedom of the crystallization water molecules involved in these crystals.

Temperature dependences of pyroelectric, piezoelectric and dielectric responses of glycine phosphite crystals doped with glycine phosphate, in temperature interval 120–320 K, have been investigated. It was established that, unlike the undoped crystals, glycine phosphite crystals grown from the solution containing 25% of glycine phosphate reveal strongly asymmetric hysteresis loops below ferroelectric phase transition temperature T C , and considerable pyroelectric and piezoelectric activity was observed both below and above T C . Analysis of the shape of the hysteresis loops and temperature dependences of dielectric permittivity with and without external biasing points to the existence of internal bias field ∼ 5 kV/cm along the twofold symmetry axis. Possible origin of the internal bias field is discussed.

Highly inhomogeneous electronic structure of Pb(Ti,Zr)O3 sol-gel thin ferroelectric films with metal electrodes including a n-type semiconducting near-electrode layer and a p-n junction in the film's interior is revealed by means of a dielectric spectroscopy and photoelectric study. Charged oxygen vacancies accumulation near the electrodes is believed as a reason for a decrease of coercive field with decreasing a speed of a bias voltage variation during measurement of C-V dependences in Ni/PZT/Pt thin film structures. Slow capacitance relaxation and transient charging/discharging currents in laser ablated (Ba,Sr)TiO3 thin films with conducting oxide electrodes after a step voltage switching on and off are explained by the p-n junction formation due to the oxygen vacancy redistribution and near-electrode Schottky barriers charging/discharging processes.

Temperature dependences of the pyroelectric, piezoelectric, and polarization responses of glycine phosphite crystals containing different amounts of glycine phosphate were studied in the range 120–320 K. The experimental data obtained suggest the presence of a built-in bias field oriented along the twofold symmetry axis in these crystals. This field was found to be 5 kV/cm. It is suggested that the built-in bias plays a decisive role in the formation of the pyroelectric and piezoelectric crystal responses in the temperature interval 225–280 K, which is significantly higher than the ferroelectric phase transition point in nominally pure glycine phosphite crystals (224 K).

An impedance analysis of Ni/Pb(Zr,Ti)O3/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO3 thin films between SrRuO3 electrodes.

Slow dielectric relaxation in barium strontium titanate thin film capacitor structures with strontium ruthenate electrodes has been investigated. It is shown that in the films containing a relative...

Photoelectric phenomena were investigated in sol-gel derived lead zirconate-titanate (PZT) films. Two major illumination techniques were employed in order to assess both the ferroelectric polarization and internal field in the films. Using semitransparent top electrodes and short UV pulses, the fast polarization-dependent photocurrent was observed and attributed to bulk photovoltaic effect. This current can be used for non-destructive readout of polarization state in non-volatile ferroelectric memories. In the other regime, opaque electrodes were employed and a steady-state current (or voltage in the open circuit conditions) was investigated caused by the illumination of the area adjacent to the top electrode This polarization-independent current was ascribed to the internal field due to oxygen-deficient layer near the film's surface. It is shown that the observed photocurrent is sensitive to the wavelength of the light and can be used for the evaluation of electron band bending and electrical in...

A novel hybrid sol–gel approach is developed to prepare composite PZT films in the thickness range 1–20 μm at relatively low sintering temperatures ( 5 μm) are fabricated using sedimentation of the PZT powder onto Pt-coated Si substrates with a subsequent multiple infiltration of powder coatings with PZT sol–gel solution. Dielectric and ferroelectric properties of thick films are studied and discussed in the framework of existing models of composites.

Effect of the speed of bias voltage variation v on the dielectric non-linearity of metal-PZT-metal thin film capacitors has been studied. A distance ΔV between two maxima of C-V dependence on the voltage scale, characteristic for ferroelectric phase, as a function of the v value was investigated. It was established that decreasing vvalue led to ΔV decrease: ΔV = 1.8–2.0 V when v = 1.6x104 V/s, and ΔV ≅ 1.0 V when v = 6.5x10−2 V/s. The ΔV(v) dependence can be explained by the decreasing of the coercive field of the film due to the migration of charged mobile defects such as the doubly ionized oxygen vacancies, and the formation of space charge regions near the electrodes. Using the experimental data some parameters of the migration process were evaluated: the concentration of oxygen vacancies and their mobility were found to be about 1024 m−3 and 10−11 m2/Vs, respectively. These values are close to the data published in the literature obtained using the alternative methods of investigation.

The capacity-voltage (C-V) characteristics of thin ferroelectric PZT films are investigated, varying the rate of change of the control voltage in a wide range. It is established that the distance between the maxima of the C-V characteristics decreases as the rate of the voltage change is decreased. This effect is caused by the decrease of the coercive field due to the spatial separation of mobile charge carriers under the action of the control field and the accumulation of charged defects in the near-electrode regions of the films. Parameters characterizing the formation of the bulk charge in the films (concentration and mobility of oxygen vacancies) are estimated. The estimations made are consistent with the literature data.

The photoelectric characteristics (independent of ferroelectric polarization) of metal-ferroelectric- metal thin film structures upon exposure to radiation in different ranges of mercury arc lamp spectrum are stud- ied for the Pb(Zr 0.5 2Ti 0.48 )O 3 ( PZT ) ferroelectrics. The PZT films on platinized silicon substrates were prepared by the sol-gel technique. The relaxations of the short-circuit current and the open-circuit voltage are investi- gated at different intensities of light with wavelengths in the range 300-1200 nm. It is found that the open-cir- cuit voltage returns to its original value after the cessation of light exposure and a short-term holding of struc- tures in the short-circuited state. The factors responsible for the photocurrent and the photoemf are analyzed, and the conclusion is made that they are predominantly contributed by the barrier photovoltaic effects associ- ated with the presence of the p - n junction in the bulk of films and the Schottky barrier in the film region adjacent to the lower platinum electrode. © 2000 MAIK "Nauka/Interperiodica".

The possibilities of using ferroelectric materials for new generations of integrated circuits for high-density dynamic memory (up to 1 Gbit per crystal) are discussed. The correspondence of the specific capacitance and leakage currents of thin film ferroelectric capacitors to the requirements for integrated circuits with various information capacities is examined. It is shown that the capacitance-voltage characteristic of the ferroelectric strongly influences the specific capacitance and the rate of decrease of the voltage across the capacitors when they are discharged in the process of storing information. The prospects for increasing the specific capacitance of memory capacitors using relaxor ferroelectrics are examined.

The parameters of the Colle-Colle-type distribution function for the time constant of Pb(Zr0.52Ti0.48)O3 thin-film layers and the pattern of the bulk resistivity distribution through the film thickness have been derived from measured frequency dependences of the complex capacitance of metal-PZT-ferroelectric-metal thin-film structures within the 100 Hz to 100 MHz range.

A study has been made of the dependence of switched charge in ferroelectric lead-zirconate-titanate films on the number of polarization reversal cycles produced by bipolar voltage pulses of fixed amplitude and duration under variation of their repetition rate. The film fatigue in the polarization switching frequency range studied (100 Hz - 100 kHz) has been shown to be dominated by the depolarization field caused by the presence in the near-electrode film regions of a pyrochlorestructure nonferroelectric phase.

Crystal structure and electrical properties of PZT thin 200 nm films deposited on Si substrates with a 100/20 nm Pt/Ti sublayer were investigated by varying conditions of thermal treatment during gel drying and using different metals as the top electrode. Under definite conditions of gel drying a strong / textured films were obtained as a result of artificial epitaxy caused by stresses in the films due to their non-uniform shrinkage after drying and high temperature treatment. The electrical measurements indicate an essential role of near-electrode ionic processes and surface barriers in forming of metal-ferroelectric-metal thin film structures properties.

Transient currents in SrRuO3//Ba0.8Sr0.2TiO3//SrRuO3 thin film capacitors, in the time interval 0.05–2.5 s after the step voltage switching on and off, have been investigated. The origin of these currents is proposed, including two components: charging (discharging) of near-electrode potential barriers and oxygen vacancy migration. It has been established that transient current of capacitor charging is mainly determined by the barrier component, and transient current of capacitor discharging is due to both components. The parameters of potential barriers were determined giving a good agreement of the calculated time dependences of transient currents with the experimental data.

Capacitance relaxation in Ba0.8Sr0.2TiO3 thin film structures has been investigated. Slow decrease of the capacitance after a bias voltage switching on is explained by suppressing the film dielectric permittivity by the field of a p-n junction originated as a result of the oxygen vacancy migration in the bias field. After the bias switching off, the p-n junction gradually disappears due to the vacancy diffusion, and the capacitance increases. The relation determining capacitance increase after the bias switching off has been obtained in agreement with experimental data. The proposed relaxation mechanism is considered as a certain type of the size effect when the p-n junction depleted region spreads over the film thickness.

In the paper, the description of the dielectric and ferroelectric properties of BaTiO_3 single crystals using Landau thermodynamic potential is addressed. Our results suggest that when using the sixth-power free energy expansion of the thermodynamic potential, remarkably different values of the fourth-power coefficient, \beta (the coefficient of P^4_i terms), are required to adequately reproduce the nonlinear dielectric behavior of the paraelectric phase and the electric field induced ferroelectric phase, respectively. In contrast, the eighth-power expansion with a common set of coefficients enables a good description for both phases at the same time. These features, together with the data available in literature, strongly attest to the necessity of the eighth-power terms in Landau thermodynamic potential of BaTiO_3. In addition, the fourth-power coefficients, \beta and \xi (the coefficient of P^2_i P^2_j terms), were evaluated from the nonlinear dielectric responses along [001], [011], and [111] orientations in the paraelectric phase. Appreciable temperature dependence was evidenced for both coefficients above T_C. Further analysis on the linear dielectric response of the single domain crystal in the tetragonal phase demonstrated that temperature dependent anharmonic coefficients are also necessary for an adequate description of the dielectric behavior in the ferroelectric phase. As a consequence, an eighth-power thermodynamic potential, with some of the anharmonic coefficients being temperature dependent, was proposed and compared with the existing potentials. In general, the potential proposed in this work exhibits a higher quality in reproducing the dielectric and ferroelectric properties of this prototypic ferroelectric substance., Comment: 7 figures, 5 tables

By analyzing Landau's phenomenological thermodynamic potential, we propose a few ways to assess the importance of eighth-power terms and to verify the temperature dependence of the anharmonic coefficients. It is demonstrated that the eighth-power terms should be substantially involved for the adequate description of the thernodynamic behavior of BaTiO 3 around the cubic-tetragonal phase transition. In addition, the temperature dependence of the anharmonic coefficients (at least of the quartic coefficients) is experimentally evidenced to be essential. Both necessities attest to the anomalously strong anharmonicity of this substance.

Electronic structure of ferroelectric thin films, characterized by electric potential and conductivity distribution through the film thickness, and the presence and the location of trap levels in a band gap influences appreciably the exploiting parameters and reliability of various ferroelectric thin-film devices including capacitors, piezo-, pyro-, electro- and acusto-optic- devices, memories etc. [1].

Protein aminoacid-based compounds were synthesized, and their single crystals were grown. The dielectric and pyroelectric properties of the crystals were studied in the temperature ranges 80–340 and 140–340 K, respectively. It was established that three of the compounds studied (L-His(H3PO4)2, L-TyrHCl, L-Ala2H3PO3 · H2O) are linear pyroelectrics, with their room-temperature pyroelectric figures of merit being close to those of ferroelectric triglycine sulfate crystals.

An analysis is made of the state of Sb and Fe impurities introduced separately and jointly into TiO2. It is found that, irrespective of the concentration and synthesis conditions, antimony impurity atoms are characterized by the same state of Sb5+ ions, whereas the state of iron impurity atoms (Fe3+) depends on the above factors. Starting from the direct observation of trivalent titanium ions, the mechanism of converting TiO2 into a semiconductor by doping it with Sb2O5 or by reduction is discussed. Also discussed is the compensating effect of Fe2O3 impurity in antimony-doped titanium dioxide, which effect consists in the „capturing” of antimony atoms due to the chemical interaction, the most plausible mechanism of which is the formation of complexes. [Russian Text Ignored]

Alkaline-earth-titanate-based electronic ceramics are widely used in the fabrication of modern products such as capacitors, varistors, thermistors, etc.1,2 The sintering of electronically active ceramics is one of most complicated and critical operations that determine the performance and cost characteristics of such products. To gain a deeper insight into the mechanisms of the sintering of the above materials and to explore the ways of promoting this process, we studied both experimentally and theoretically mass transfer processes in sintering alkaline-earth titanates.