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.     

Influence of the humidity on dielectric characteristics of porous aluminum oxide with inclusions of triglycine sulfate

The temperature dependences of the capacitance and conductance measured for samples of porous aluminum oxide films with inclusions of triglycine sulfate have been investigated. The character of these dependences obtained for the films treated in a humid atmosphere differs from that of the corresponding dependences measured for the initial porous Al₂O₃ matrix, bulk triglycine sulfate, and dried Al₂O₃ + triglycine sulfate composite. The observed changes are determined by the influence of the water adsorbed on the surface of the film and the water structured in pores of the composite.     

The impedance-characteristic method in the study of specific temperature features of dielectric anomaly suppression in triglycine sulfate

The reflection and absorption coefficients in a waveguide loaded on ferroelectric triglycine sulfate (TGS), which has a layered domain structure near the phase transition, are calculated by the impedance-characteristic method. The calculated and experimental data do not reveal any correlations with the specific temperature features in the TGS dielectric response to microwave irradiation. The mechanism of the microwave effect is discussed.     

Phase transitions in crystals of protein amino acids

The temperature dependence of the piezoelectric response of many protein amino acids and their compounds exhibits a sharp increase in the piezoelectric response signals at a certain temperature. It has been shown using the example of the known ferroelectrics without a piezoelectric effect in the paraphase (triglycine sulfate, glycine phosphite, trisarcosine calcium chloride) that such an increase in the piezoelectric response is associated with the structural phase transition to the low-symmetry piezoelectric phase with a large number of piezoelectric coefficients. The specific features of the phase transitions with the symmetry change D ₂-C ₂ have been discussed.     

Magnetic properties of porous glass-CuO nanocomposites

The magnetization of the porous glass nanocomposite with CuO nanoparticles embedded in the pores has been studied in the temperature range from 1.8 to 350 K for different pore fillings. It has been shown that the magnetic properties of these nanocomposites depend significantly on pore filling. It has been found that, in the low-temperature range for the nanocomposite with a pore filling of 55% and for pressed CuO, the ZFC and FC susceptibilities diverge, a feature which has been almost absent in the nanocomposite with 21% filling. It has been demonstrated that the kink in the temperature dependence of magnetization, which corresponds to the paramagnetic-multiferroic phase transition, does not shift in the sample with a larger pore filling as compared to that observed in the bulk sample.     

Relaxation of the domain structure in doped triglycine sulfate crystals in an internal field

This paper reports on the results of an investigation into the relaxation of the domain structure of triglycine sulfate ferroelectric crystals from a nonequilibrium state induced by rapid cooling of the sample through the phase transition point, in response to an external electric field, and under thermal annealing. The role played by the internal field in the processes of relaxation of the domain structure to the equilibrium state in defect-containing triglycine sulfate crystals is elucidated.     

Dielectric loss as an indication of the kinetics of the ferroelectric phase transition

The dependences tanδ(f, T) for triglycine sulfate and diglycine nitrate single crystals are investigated in the frequency range f = 1?2 × 10⁷ Hz at temperatures from ?150 to 50°C for triglycine sulfate and from ?150 to ?60°C for diglycine nitrate. The results are discussed in the framework of the model according to which two or more types of media with different dielectric properties are formed in the ferroelectric phase. The polar volumes of domains themselves and the volumes of domain walls with different symmetries are treated as individual media. The dependences tanδ(f, T) make it possible to separate the contribution of a particular medium and to trace its evolution with temperature. The results of the analysis of the relaxation properties confirm that the phase transitions lead to the formation of two media (the polar medium and domain walls) in triglycine sulfate and three media (the polar medium and two types of domain walls) in diglycine nitrate. It is demonstrated that the relaxation properties are not steady-state characteristics of the samples but depend on their prehistory.     

Relaxation of static photoelasticity in triglycine fluoroberyllate crystals

The relaxation of the static photoelasticity in triglycine fluoroberyllate crystals has been studied. The anisotropy of the relaxation amplitudes and their anomalies near the phase transition have been revealed. The photoelastic relaxations and peculiarities of their temperature behavior have been explained in terms of the piezocaloric mechanism.     

Temperature-induced orientational transition of nematics on the surface of a ferroelectric crystal

A temperature-induced orientational transition is investigated in a mixture of nematic liquid crystals on the surface of a cleavage of a ferroelectric triglycine sulfate crystal. The transition has been observed by the variation of the polarized absorbance components of a dye introduced into the nematic matrix with increasing temperature. The reorientation of molecules in the liquid crystal volume confined by solid walls is due to competition between dispersion and polar forces at the surface and the decrease in the electric field of the substrate up to its complete disappearance at the ferroelectric Curie point.     

Dielectric properties of a triglycine sulfate crystal grown with a transition through the Curie point

The dielectric properties of the triglycine sulfate (TGS) crystal grown by lowering the temperature with a transition through Curie point T_C during its growth are studied. The greatest values of low-frequency dielectric permittivity ε_max(T = T_C) and effective dielectric permittivity ε_eff(E₀) correspond to the layer of crystal formed at the temperature of the phase transition.     

Attenuation of finite amplitude sound near the ferroelectric phase transition

The temperature dependences of the effective sound attenuation near the phase transition in the triglycine sulfate crystal are calculated for powerful acoustic waves with a strain of an order of 10^?5. It is demonstrated that the generation of harmonics and their absorption can appreciably contribute to the measured absorption coefficient at the basic frequency owing to a critical increase in the third-order elastic moduli. The calculated data are compared with the experiment.     

Nanotubes of piezoelectric BNT–BT0.08 obtained from sol–gel precursor

The results of investigations of porous glasses (PG) and porous glasses–ammonium hydrogen sulfate ferroelectric nanocomposites (AHS–PG) are presented. On the basis of dielectric and calorimetric measurements it was shown that in the AHS–PG nanocomposites with average pore size of 44, 68, 95, and 320 nm the anomalies of dielectric permittivity and specific heat similar to those in bulk crystals AHS are observed. An influence of the mean value of pores sizes on the ferroelectric phase transition temperatures of AHS nanocrystals embedded into the porous matrices was determined. It was shown that in AHS–PG dispersion of the dielectric permittivity is observed in both para- and ferro-electric phases and above room temperature AHS–PG nanocomposites exhibit the ionic conductivity.     

Change in dielectric properties of triglycine sulfate in a constant magnetic field

The effect of a constant magnetic field on the dielectric properties of triglycine sulfate crystals has been investigated. It has been shown that, after the magnetic treatment of the crystal (2 T, 20 min), the hysteresis loop becomes narrower; i.e., the coercive field decreases, and the dielectric permittivity changes in the region of the phase transition. It has been found that the observed effect is anisotropic with respect to the orientation of the crystal in a magnetic field and occurs when the vector of magnetic induction is perpendicular to the polar axis of the crystal. The relative orientation of the magnetic field and the domain structure determines its sign. The doping of the crystal with chromium makes the effect more pronounced and leads to a change in the kinetics of the magnetically stimulated increase in the dielectric permittivity.     

Dielectric dispersion as an indication of the formation of a polar phase in ferroelectrics

The regularity of the appearance of dispersion in the rf range immediately at the Curie point upon transition to the polar phase is demonstrated using the three-dimensional dependences of the permittivity ε ₂₂ ^′ (f, T) for a triglycine sulfate single crystal as an example. This regularity is common to all ferroelectrics and can be used for the direct objective determination of the phase transition temperature.     

Properties of nanoporous aluminum oxide with triglycine sulfate and Rochelle salt inclusions

The possibility of producing the ferroelectric state in nanoporous aluminum oxide loaded with triglycine sulfate and Rochelle salt has been studied. Our dielectric, pyroelectric and emission measurements give grounds to suggest that this state persists in the composites under study up to temperatures exceeding the Curie point of bulk crystals by several tens of degrees.     

Phase transitions in KNO3 embedded in MCM-41 films with regular nanopores

This paper reports on a comparative study of phase transitions in nanocomposites made up of KNO₃ embedded in 10-μm-thick MCM-41 films with unidirectional pores 4.0 nm in size on an aluminum substrate and of nanocomposites prepared in the form of potassium-nitrate-filled pressed MCM-41 powders with 3.7-nm pores. The temperature dependences of linear permittivity and the amplitude of third harmonic generation have been measured under heating and cooling. The structural transition from phase II to phase I shifts under heating relative to that occurring in bulk KNO₃ toward lower temperatures for potassium nitrate in the film and toward higher temperatures for the pressed MCM-41-based nanocomposite. A significant difference has been observed also within the region of existence of ferroelectric phase III. The data obtained suggest that the shifts of phase transition temperatures observed in the conditions of nanoconfinement are influenced markedly not only by pore size and geometry but also by other factors.     

Acoustic emission upon spontaneous polarization in triglycine sulfate single crystals

We report on the results of analysis of acoustic emission (AE) under thermal action on a triglycine sulfate (NH₂CH₂COOH)₃ ? H₂SO₄ crystal. The triglycine sulfate single crystals grown from solution and not subjected to mechanical treatment are heated to a temperature above the Curie point (T_C = 49°C). During natural cooling of the crystal, a transition from the paraelectric to ferroelectric phase is accompanied by intense AE. In the temperature range ～28–30°C, an anomalous drop of the mean-square voltage in the AE signal is observed against the background of monotonic accumulation of AE events.     

Dielectric losses in the triglycine sulfate crystal under heating and cooling

Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses ε″ and by the temperature behavior of the maximum losses ε″_max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses ε″_max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat.     

Effects of composition ratio on structure and phase transition of ferroelectric nanocomposites from silicon dioxide nanoparticles and triglycine sulfate

The present work is devoted to study on influences of silicon dioxide nanoparticles (SiO₂) on structure and phase transition of a classical ferroelectric of triglycine sulfate (TGS) by synthesizing a composite containing SiO₂ and TGS at different composition weight ratios. Particle size analysis, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) techniques were utilized to charaterize the synthesized composite. The experiments for investigation of phase transition were conducted from 20 to 120°C under a weak electric field (1?V.cm^?1) at 1?kHz. The results revealed an expansion of ferroelectric phase of TGS by 15–55°C with increasing the SiO₂ content. Besides, an additional phase transition point which is characteristic for the bulk clusters of TGS was found at low content of SiO₂. The detected anomalies were discussed thoroughly based on the interaction between components in the composite.     

Ising model for a ferroelectric phase transition in a system of interacting small particles

An approach based on the Ising model has been proposed for describing a ferroelectric phase transition in a system of interacting identical small particles. It has been found that the shift of the phase transition temperature with respect to the transition point in a bulk sample is affected by both the size effects due to the smallness of the particles and their interaction with each other. The behavior of the dependence of the phase transition temperature on the distance between particles is determined by the nature of the interparticle interaction. An analysis has demonstrated that the interaction between small particles should be taken into account in the interpretation of the ferroelectric properties of nanocomposite materials.