Search

Subsonic flows of different gases in the near field of inert and reacting jets is experimentally investigated. The jets flowed out of long tubes, 2 to 8 mm in diameter, into an air medium at low Reynolds numbers from 400 to 5000. The working fluids were air, carbon dioxide, propane, and Freon-22 for inert isothermal jets and propane mixed with an inert dilution (СО2) for reacting jets. The tools included Hilbert visualization, PIV, thot-wire anemometry, and probe thermometry. A scenario of transition to turbulence through the intermittence mechanism in inert and reacting jets is revealed for the first time. It is realized in the Reynolds number range from 1900 to 3500, when laminar-turbulent transition occurs within the jet source, that is, the tube, in the absence of artificial disturbances. Turbulent spots generated in the tube in the transitional regime are statistical in nature and fairly stable in the jet near-field. Propagating downstream they can have a considerable effect on the dynamics of free jets and diffusion plumes.

Diffusion burning of a hydrogen jet is studied by methods of the Hilbert optics. A diagnostic system based on the batch-produced IAB–463M device is implemented, which includes a specially developed Hilbert filtration module coupled with a light source. The influence of local turbulent perturbations (puff or slug) arising in the tube forming the jet on the dynamic structure and flame evolution is revealed. This phenomenon can be used to control the space-time structure of the flame.

Results of an experimental study of hydrodynamics and diffusion combustion of hydrocarbon jets are presented. Various regimes of instability development both in the jet flame proper and inside the source of the fuel jet are considered. The experiments are performed for the case of subsonic gas jet expansion into the air from a long tube 3.2 mm in diameter in the range of Reynolds numbers from 200 to 13 500. The fuel is the propane–butane mixture in experiments with a cold jet (without combustion) and pure propane or propane mixed with an inert dilutant (CO2 or He) for the jet flame. The mean velocity and velocity fluctuations in the near field of the jet without combustion are measured. Among four possible regimes of cold jet expansion (dissipative, laminar, transitional, and turbulent), three last regimes are investigated. The Hilbert visualization of the reacting flow is performed. The temperature profiles in the near field of the jet are measured by a Pt/Pt–Rh thermocouple. An attached laminar flame is observed in the transitional regime of propane jet expansion from the tube. In the case of combustion of C3H8 mixtures with CO2 or with He in the range of Reynolds numbers from 1900 to 3500, the transitional regime is detected in the lifted flame. Turbulent spots formed in the tube in the transitional regime exert a significant effect on the flame front position: they can either initiate a transition to a turbulent flame or lead to its laminarization.

In this work, the experimental data are compared with the version of the “strong” jet (Re ≫ 1) of the exact Landau-Squire solution. The experiments were performed for a submerged air jet flowing out of a tube with a diameter of D = 3.2 mm and a length of more than 100D at a Reynolds number equal to Re = 436. The initial conditions in the jet are the Poiseuille velocity profile, the level of velocity pulsations is less than 1%. Measurements were carried out using a hot-wire anemometer. It is shown that satisfactory agreement with theory is achieved at distances from the tube starting from x/D = 5.6 and up to the zone of transition to turbulence (x/D > 35). Turbulence along the jet axis will increase from 1% to 2.5%, while in the mixing layers it increases to 4.7%.

The paper presents the experimental results for isothermal flows (CO2, propane) and diffusion flames (C3H8 or H2 mixed with CO2). Optical method of PIV (Particle Image Velocimetry) and flow visualization are used. The paper considers the features of the effect of vortex superstructures on an attached diffusion plume. When superstructures interact with the flame front, the question of choosing the determining scales becomes ambiguous. Apparently, the features of the perturbation interaction can depend on the acoustic characteristics of the flows and, accordingly, on the nature of the density distribution in the plume.

Today, the turbulent characteristics of laminar jets remain almost unexplored, although all real flows have a pulsating component, which in technological processes can have a significant effect on the processes of mixing, heat and mass transfer. The turbulent characteristics of a submerged laminar air jet flowing out of a tube with a diameter of 3.2 mm and length of more than 100 diameters were experimentally investigated at Reynolds number of 436. The measurements were carried out using a hot-wire anemometer. The ranges of operating parameters at which the laminar, transitional and turbulent flows occur in the jet source have been determined. Based on the data obtained, the regime for the study was selected. For the selected regime, the profiles of average velocities and pulsations in cross-sections along the jet flow were measured and distributions of turbulent characteristics along the jet flow on the axis and in the mixing layers were constructed.

We have experimentally studied subsonic submerged air jets emitted from flat mini and micro nozzles with characteristic dimensions from 22 to 600 μm in a range of Reynolds numbers 70–2600. The point of laminar-turbulent transition (jet penetration range) was determined using the flow visualization technique. It is established that the penetration range of micro jets can reach 100–300 nozzle calibers. The Reynolds number for the transition to turbulence in flat mini and micro jets reaches high values (1000–2600), which are two to three orders of magnitude greater than the Reynolds numbers for the loss of stability (3–10). Available experimental data are summarized and generalized based on the Reynolds number determined for the jet penetration range.

The average and pulsating thermal characteristics at the stagnation point of a plate at inflow of an impact axisymmetric air jet have been studied. The influence of the Reynolds number (100 4000, the difference in heat transfers for two cases of jet formation (from a tube and a nozzle) decreases asymptotically.

Temperature dependences of the dielectric permittivity and thermal treatment effect have been studied for (1−x)SrTiO3-(x)KTaO3 and (1−x)SrTiO3-(x)KNbO3 (0 ≤ x ≤ 0.2) solid solutions. For low concentrations x, strong dielectric relaxation was found in the temperature range of 150–250 K. A relaxing centers model based on the local charge compensation of heterovalent impurities is discussed.

The possibilities of the use of calorimetric methods to determine the important features of ferroelectrics – the temperature dependence of the spontaneous polarization and the effective correlation parameter are considered. The relationship between the temperature dependences of the specific heat and the spontaneous polarization is analyzed on an example of the high-temperature uniaxial ferroelectric crystal LaBGeO3. It is shown the particular importance of the proper separation of the anomalous part of the heat capacity from the background one for the quantitative comparison of the specific heat and the spontaneous polarization. The temperature dependence of the specific heat of the thin BaTiO3 thin polycrystalline and epitaxial films on different substrates is obtained, compared and used to determine the spontaneous polarization. The difference of the thermal properties of polycrystalline and epitaxial films confirmed the crucial role of the misfit strains and their relaxation due to formation of the gr...

The temperature dependences of the dielectric constant and dielectric hysteresis loops in ceramic samples of (1 − x)SrTiO3−x KNbO3 and (1 − x)SrTiO3−x KTaO3 (0 ≤ x ≤ 0.3) solid solutions prepared using different heat treatments have been investigated. Phase diagrams of the studied solid solutions have been constructed in the T-x coordinates. It has been shown that, after quenching of samples (spontaneous cooling at room temperature after long-term heating at the sintering temperature of the ceramic samples), the temperature of the induced phase transition increases because of the weakening of random electric fields associated with nonisovalent impurities due to their “frozen” nonequilibrium redistribution. For small concentrations x, strong dielectric relaxation is observed in the temperature range of 150–250 K. A model of relaxing centers, which is based on the local charge compensation of heterovalent impurities, has been proposed.

Heat transfer of round impinging jets has been investigated in a wide range of Reynolds numbers (Re=40-21000). A jet flowing out of a profiled nozzle and a long tube at a constant wall temperature and at a distance to the obstacle h/d=1-20 was studied. In experiments at Re3000, the difference in heat transfer for the two variants of jet formation (from the tube and from the nozzle) decreases asymptotically. For laminar and turbulent flow modes, the results of numerical calculations are consistent with the experimental data.

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions ∼(50–100) μm and a thickness d ∼ (1–5) μm have been grown by evaporation on NdGaO3(100) and α-Al2O3 substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The c* (Z) crystallographic axis in the blocks is normal to the film plane, and the a (X) axis and the polar axis b (Y) are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature T c depends on the degree of deuteration D of the glycine phosphite. The maximum value T c = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite D ∼ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.

The phenomenological theory of solid solution is used to calculate the material constants (elastic compliances, susceptibilities, piezoelectric moduli, pyroelectric constants) of Ba x Sr1 − x TiO3 solid solutions over the entire range of concentrations x at room temperature. The phenomenological potential constants and the numerical values of the material constants are given for specific concentrations.

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.

The aim of this work is an experimental study of the flow in subsonic free and impinging macro- and microjets of air. Complex measurements have been performed using the PIV method (Particle Image Velocimetry), hot-wire anemometry and flow visualization. In the experiments, we used the axisymmetric and flat micronozzles with the characteristic size of 250−600 µm. The measurement performed for the jets of the larger size of 1−8 mm are presented for comparison and generalization of experimental data. Air, whose thermodynamic parameters are close to the atmospheric conditions, was used as the working gas. Flow visualization allowed us to construct the spatial pattern of formation and decay of the laminar part of the jet and transition to turbulence. It was shown that the range of a free jet can equals 100−200 nozzle sizes. The Reynolds number of transition to turbulence in mini- and microjets takes high values (1000−2600), and this is two-three tens times higher than the Reynolds number of stability loss. In the impinging jet, an obstacle can change the coordinate of transition to turbulence, for instance, due to the feedback effect.

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.

Thin polycrystalline films of amino acid ferroelectrics glycine phosphite (GPI) have been prepared by evaporation method on NdGaO3(001) substrate with interdigital structure of electrodes deposited on the surface. Optical images of films obtained by means of polarized microscope in reflection mode have shown that the films consist of small single crystal blocks of several tens of microns in size. X-ray diffraction analysis proves that the non-polar c* axis in blocks coincides with the normal to the surface, and the polar axis b is oriented in the film plane. Temperature dependences of capacitance of GPI/NdGaO3 structures measured using interdigital structure of electrodes exhibit strong anomaly at ferroelectric phase transition temperature of glycine phosphite single crystals. Dielectric hysteresis loops in glycine phosphite films were measured by Sawyer-Tower method. The difference in frequency dependence of coercive field and remnant polarization in structures with GPI and previously studied betaine pho...

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 D2-C2 have been discussed.

Poly- and single-crystal films of betaine phosphite deuterated to ∼20% have been grown by evaporation on NdGaO3 (001) substrates with a preliminarily deposited planar interdigital structure of electrodes. The small-signal dielectric response in the 0.1–100.0-kHz frequency range has revealed a strong anomaly in capacitance upon the transition of the films to the ferroelectric state. Application of a bias field brings about suppression and a slight shift of the dielectric anomaly toward higher temperatures. The strong-signal dielectric response has been studied by the Sawyer-Tower method over the frequency range 0.06–3.00 kHz both in the para- and ferroelectric phases. In contrast to the case of a plane-parallel capacitor, in the planar structure studied, the dielectric hysteresis loops exhibit a very small coercivity at low frequencies, which grows with increasing frequency. This difference should be assigned to different domain structures formed in a planeparallel capacitor and in a planar structure in a saturating field. The growth of hysteresis with increasing frequency in a planar structure is considered to be associated with the domain wall motion.

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.

Polycrystalline films of betaine phosphite (BPI) and deuterated BPI have been grown by evaporation on LiNbO3, α-SiO2, α-Al2O3, and NdGaO3 substrates. These films consist of large single-crystal blocks in which the polar axis (b) lies in the substrate plane. The results of studying the dielectric properties of the films using interdigital electrodes, X-ray diffraction, and block images in a polarized-light microscope in reflection are reported. The film transition into the ferroelectric state at T = Tc is accompanied by strong anomalies of the capacitance of the film/interdigital structure/substrate structure. The deuteration of BPI films leads to an increase in their temperature Tc: from Tc = 200 K for BPI-based structures to Tc = 280 K for structures with a high degree of deuteration (d ∼ 90%).

Temperature dependence of the dielectric constant and longitudinal acoustic wave velocity were studied in betaine phosphite—betaine phosphate single crystals (BPI1-xBPx: x = 0−0.1) in temperature regions of antiferrodistortive (Tc1) and ferroelectric (Tc2) phase transitions. The admixture of BP to BPI leads to increase of the antiferrodistortive phase transition temperature Tc1(x) (Tc1(0.1) = 360 K, Tc1(0) = 355 K) and decrease of the dielectric anomaly at Tc1(x). The nonlinear temperature dependence of the inverse dielectric constant in the antiferrodistortive phase, the electric field effect on the dielectric constant and acoustic anomalies at the ferroelectric phase transition are described in the frames of the Landau-Ginzburg-Devonshire-type thermodynamic model with the biquadratic coupling between nonpolar and polar order parameters.

A short review of the study of thermal properties of the nanostructured ferroelectrics is given. An application of the modern calorimetric technique to a comparative study of phase transitions in the ferroelectric nanostructured materials (polycrystalline and epitaxial thin films, superstructures, ferroelectric heterostructures, substrate-induced ferroelectricity) is considered.

Single crystals of Na1/2Bi1/2TiO3-KTaO3 (NBT-KT) solid solutions have been grown for the first time. The elemental composition of as-grown single crystals determined by X-ray diffraction corresponds to 0.81 NBT-0.19 KT. Measurements of the temperature dependences of dielectric characteristics showed that the obtained NBT-KT crystals possess clearly pronounced relaxor properties.

The effect of Li on the phase state of SrTiO3 was studied to clarify the predominant factors of induced polar state in incipient ferroelectrics. Dielectric, ultrasonic and polarization loops measurements were carried out in a temperature range of 3–350 K using ceramic samples of Li x Sr1-x TiO3-x/2 (0 ≤ x ≤ 0.05). The observed relaxor-like features are attributed to a possible polar state arising from off-centre Li+ ions in the perovskite SrTiO3 lattice. The transition from the thermally activated regime to quantum tunneling is observed at T < 6 K.

Perovskites PbBO3 with multiple substitutions in the B-positions were synthesized. Ceramic samples with n = 2–6 (n is the number of different B-ions) were studied using X-ray diffraction, and measurements of dielectric permittivity at frequencies 12 Hz–100 kHz and temperatures 77–450 K. It has been shown that the samples are of the perovskite structure, they undergo phase transitions from disordered to ordered phase, and their dielectric behavior is typical for relaxors. The order-disorder phase transitions proceed with the unit cell doubling. Based on this and in accordance with random site model, the B-ion distribution over two sublattices is discussed.

The PIV technique was used to measure the instantaneous vector fields of flow velocity and vorticity behind a thin cross-flow rib installed in a channel with laminar, transient, or turbulent flow. The data were treated statistically to determine the fields of mean longitudinal flow velocity and the correlations of pulsating velocity components 〈u′ν′〉 and 〈u′u′〉. Some features of the flow structure developing under conditions of laminar-turbulent transition behind the rib have been revealed.

The anisotropy of the piezoelectric response in diserine sulfate single crystals has been studied at room temperature. The electromechanical coupling coefficient and the piezoelectric coefficients have been evaluated.

This paper reports on the synthesis of PbBO3 perovskites with mixed-valence substitution in the B position in which the number of ions n in different valence states occupying oxygen octahedra varies from 2 to 6. The dielectric properties of ceramic samples have been studied at frequencies in the range from 12 Hz to 100 kHz and in the temperature interval 77–450 K. The new compounds have been shown to possess relaxor properties.

In the second part of review, we have considered the problems related to momentum and heat transfer in nanofluids. Results on hydrodynamic friction, forced and free convection in the laminar and turbulent flows are analysed; heat transfer at boiling is considered. The available models describing heat transfer intensification and suppression in nanofluids are studied. It is shown that for some problems on convective heat transfer there is a contradiction in data of different authors; possible reasons for this contradiction are analysed.

Here is the review of experimental and theoretical results on the mechanism of heat transfer in nanofluids. A wide scope of problems related to the technology of nanofluid production, experimental equipment, and features of measurement methods is considered. Experimental data on heat conductivity of nanofluids with different concentrations, sizes, and material of nanoparticles are presented. Results on forced and free convection in laminar, and turbulent flows are analyzed. The available models of physical mechanisms of heat transfer intensification and suppression in nanofluids are presented. There are significant divergences in data of different researchers; possible reasons for this divergence are analyzed.

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...

Polycrystalline films of betaine phosphite (BPI) and triglycine sulphate (TGS) were grown by the evaporation method on different substrates (α-SiO2, α-Al2O3 and LiNbO3 with interdigital transducers, and Al/SiO2). Large (∼1 mm in BPI and ∼0.2 mm in TGS) single-crystalline blocks were visualized in a polarizing microscope in the reflection mode. Blocks are characterized by preferable in-plane orientation of the ferroelectric axis. Temperature dependences of the BPI and TGS film capacity at frequencies 120 Hz–1 MHz exhibit a strong maximum at the temperature of the ferroelectric phase transition of bulk crystals. The effect of a bias electric field on the dielectric constant and losses was studied. Description of dielectric properties is carried out using Landau-Ginsburg-Devonshire model with account of film-substrate interaction. Low frequency conductivity in BPI films is related to DC conductivity due to thermo-activation process with activation energy Eact ∼ 0.1 eV. AC conductivity associated wit...

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.

We have analyzed and experimentally studied compounds with an ABO3 perovskite structure with multiple substitutions in the B site by different ions in different valence states. It is shown that increasing the number of such ions n from 2 to 6 gives rise to the appearance of superstructural reflections in the X-ray diffraction spectra of the corresponding compounds. These reflections evidence a phase transition to an ordered state with cell doubling and the order-disorder phase transition temperature of not less than 1000°C.

Polycrystalline films of betaine phosphite are grown on single-crystal quartz and lithium niobate substrates atop interdigitated transducers. It is revealed using a light-polarizing microscope in the reflection mode that the films are made up of large (up to 1 mm in size) single-crystal blocks. The temperature dependences of the film capacitance measured at frequencies from 120 Hz to 1 MHz pass through a strong maximum at the ferroelectric phase transition point. The effect of a bias on the permittivity of the films is investigated. It is shown that the differences in the temperature dependences of the permittivity of single crystals and films originate from the influence of dynamic strains in the substrate on the film and from the presence of an effective depolarizing field.

The temperature (295 K < T < 650 K) investigations of the polarized Raman spectra measured for a single-crystal sample of the Pb0.54Ca0.46TiO3 solid solution in the frequency range 10 < ν < 1200 cm−1 have established the existence of at least one specific temperature (T c ≈ 392 K) at which the oscillator parameters of phonon modes exhibit noticeable anomalies. Similar phenomena are observed in solutions with 0.4 < x < 0.5. A sharp increase in the intensity of the spectral lines corresponding to polarization waves at temperatures immediately below T c suggests a transformation of Pb1 −x Ca x TiO3 (0.4 0.5.

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 temperature dependence of the heat capacity of thin epitaxial films BaTiO3/MgO is studied by the dynamic 3ω method in the thickness range 50–500 nm. It is revealed that the heat capacity exhibits diffuse anomalies due to phase transitions. The temperature of the ferroelectric phase transition T C increases with decreasing film thickness. The reasons for the strong diffuseness of the transition and the nonlinear dependence of the transition temperature on the film thickness are discussed.

We performed a study of the temperature dependence of the dielectric response of (Ba,Sr)TiO 3 (BST) ceramics for the whole composition range in a wide frequency range by means of Fourier transform infrared, time-domain THz, microwave and low-frequency dielectric spectroscopy. Room-temperature spectra of the paraelectric dielectric response were compared with the results of first-principle simulations within the effective Hamiltonian approach with a good semi-quantitative agreement. It is shown that in the paraelectric phase away from the transition temperature, the complex THz soft mode, consisting of two overlapping heavily damped oscillators, fully accounts for the low-frequency dielectric properties. However, close to T C additional central-mode type dispersion, apparently caused by the pre-transitional polar clusters, is to be expected in the microwave dielectric spectra.

It is shown that the information about thermophysical parameters of the nanostructured ferroelectrics is a useful supplement to the traditional x-ray and dielectric data. The results of the study of the temperature dependence of heat capacity of BaTiO 3 /MgO epitaxial thin films by dynamical 3ω method for the thickness range 50–450 nm are presented. The blurred specific heat anomalies corresponding to the phase transitions were observed, and the temperature of the transitions increases with decreasing of film thickness compared with T c in a bulk sample. The causes of the severe smearing of specific heat anomalies as well as pronounced nonlinearity of the dependence of the transition temperature on the film thickness are discussed. Specific heat data for ferroelectric superlattices (BaTiO 3 ) n /(Sr TiO 3 ) m /Sr TiO 3 were obtained for the first time for the films with the average thicknesses near 100 nm.

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.

Ceramic samples of (1 − x)SrTiO3-xLiNbO3 (0 ≤ x ≤ 0.05) solid solutions are synthesized. The dielectric and acoustic properties of the solid solutions are studied in the temperature range from 15 to 300 K. It is revealed that the polar state characterized by the dispersion of the permittivity and the dielectric hysteresis occurs at low temperatures. The results obtained are discussed within the concept of relaxor ferroelectrics.

A short review on BaTiO 3 -based solid solutions is presented. The (x – T) phase diagrams are discussed (x is the molar concentration of the second end-member of a solid solution). Two specific points in the phase diagrams of many solid solutions are determined. These points are points of the convergence of three phase transition lines at x mph and points of the transformation of the normal ferroelectric states into the relaxor ferroelectric states at x F − R . Examples of experimental dependences and a table with parameters of solid solutions are presented.

Phase transitions in ceramic samples of (1 − x)BaTiO3-xBa(Mg1/3Nb2/3)O3 solid solutions were studied by differential scanning calorimetry for x = 0, 0.01, 0.02, and 0.03 in the temperature ranges 255–290 K and 310–410 K. The experimental data obtained were used to derive the thermodynamic parameters of the phase transitions occurring at T c ≈ 400−300 K and T 1 ≈ 290−300 K and construct the concentration phase diagram.

Between numerous ferroelectrics and related materials, there are several crystals which have a polar soft mode but do not exhibit a ferroelectric phase transition. These crystals are SrTiO3, KTaO3,...

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.