Doping-induced local symmetry breaking of centrosymmetric molecular crystals endows them with piezoelectric and pyroelectric properties. In this work, we measured temperature dependences of pyroelectric and piezoelectric coefficients in α--glycine crystals single-doped by threonine and double-doped by threonine and alanine. We analyzed primary and secondary pyroelectric effects in these crystals and suggested a model of the dopant complexes related to the observed effects. Keywords: pyroelectricity, α-glycine, doped molecular crystals.

Синтезированы твердые растворы (1-x)SrTiO_3-xPbZrO 3 (x=0.5, 0.6, 0.7, 0.8, 0.9) и исследованы их диэлектрические свойства. Измерение петель диэлектрического гистерезиса позволило получить полевые зависимости основных параметров, характеризующих эффект сохранения энергии в этих материалах. Обсуждается связь полученных параметров с эволюцией состояния твердых растворов от релаксоров до антисегнетоэлектриков в данной системе. Ключевые слова: твердые растворы, эффект сохранения энергии, релаксоры, антисегнетоэлектрики.

Doping-induced local symmetry breaking of centrosymmetric molecular crystals endows them with piezoelectric and pyroelectric properties. In this work, we measured temperature dependences of pyroelectric and piezoelectric coefficients in α-glycine crystals single-doped by threonine and double-doped by threonine and alanine. We analyzed primary and secondary pyroelectric effects in these crystals and suggested a model of the dopant complexes related to the observed effects.

Solid solutions (1-x)SrTiO 3-x PbZrO 3 (x=0.5, 0.6, 07, 0.8, 0.9) were synthesized and their dielectric properties are investigated Measurement of dielectric hysteresis loops allowed us to obtain field dependences of the main parameters characterizing the effect of energy storage in these materials. The relationship of the obtained parameters with the evolution of the state of solid solutions from relaxors to antiferroelectrcs in this system is discussed. Keywords: solid solutions, energy storage effect, relaxors, antiferroelectrcs.

Temperature response of a material to an external electric field is the main method for electrocaloric effect study in ferroelectrics. In this work, for 0.65PbFe2/3W1/3O3-0.35PbTiO3 solid solution as a model object, it is shown that with an increase in the electric field strength, current filamentation effect can occur. It leads to formation of local regions of increased conductivity in the sample. The associated thermal effect have short characteristic times, due to the small volume of the filament. They are comparable to the times of the electrocaloric response of the material, and can lead to significant errors in the detection of the electrocaloric effect. Keywords: electrocaloric effect, temperature response, ferroelectric ceramics, current filamentation effect.

Abstract A new approach to pyroelectric research based on the information-measuring theory of dynamical systems is presented and substantiated. The proposed technique is based on direct monitoring of both the sample temperature using a fast infrared sensor and pyroelectric current allowing precise quantification of the pyroelectric coefficient of bulk and film materials with high reliability and accuracy over a wide range of temperature and applied electric field. The capabilities of the method are demonstrated on AlN films, α-glycine crystals, and ferroelectrics.

A new experimental approach to the complex study of electrocaloric, pyroelectric, and thermal effects associated with the bulk and local electrical conductivity of ferroelectrics and related materials is proposed. The key to this approach is the analysis of the dynamics of the sample temperature response to an arbitrary external action, including long-term electrical impacts. The metrological justification of the experimental technique is based on direct non-contact high-speed monitoring of the sample temperature using an IR photodiode sensor designed by Ioffe Institute. Its efficiency is confirmed by numerous experimental data on electrocaloric properties of ferroelectrics, relaxors, and relaxors-based multilayer structures.

Monolithic optical sensors based on low shunt resistance p-InAsSbP/n-InAs and p-InAsSbP/n-InAsSb heterostructures grown onto low-resistivity n-InAs substrates equipped with transimpedance amplifiers suffer from output electrical signal distortions. The paper presents analysis of the above distortions and an equivalent circuit for output electrical signal analysis and measurements, as well as recommendations for suppression of interference of signal components has been suggested. Keywords: optical sensors, ATR sensors, optopairs, p-InAsSbP/n-InAs(Sb) heterostructures

Monolithic optical sensors based on low shunt resistance p-InAsSbP/n-InAs and p-InAsSbP/n-InAsSb heterostructures grown onto low resistivity n-InAs substrates equipped with trans-impedance amplifiers suffer from output electrical signal distortions. The paper presents analysis of the above distortions and equivalent circuit for output electrical signal analysis and measurements as well as recommendations for suppression of interference of signal components have been suggested.

A new experimental method for leakage current (conduction current) measurements in dielectrics, based on an analysis of the dynamics of temperature changes of the sample under the action of an electric field is proposed. A new non-contact photodiode IR-temperature sensor carries out high accuracy and high speed monitoring of the sample temperature response. The capabilities of the method are demonstrated on samples of 0.65 PbFe2/3W1/3O3-0.35 PbTiO3 (PFW-PT) ceramic, for which the experimental dependence of conductivity was obtained in a wide temperature range from 20 to 110 ° C.

Temperature response of a material to an external electric field is the main method for electrocaloric effect study in ferroelectrics. In this work, for 0.65 PbFe2/3W1/3O3 – 0.35 PbTiO3 solid solution as a model object, it is shown that with an increase in the electric field strength, current filamentation effect can occur. It leads to formation of local regions of increased conductivity in the sample. The associated thermal effect have short characteristic times, due to the small volume of the filament. They are comparable to the times of the electrocaloric response of the material, and can lead to significant errors in the detection of the electrocaloric effect.

A new experimental method for measuring leakage currents (conduction currents) in dielectrics, based on the analysis of the dynamics of sample temperature variation under an electric field is proposed. The temperature response of the sample is recorded with high accuracy and speed using a non-contact photodiode IR-temperature sensor. The method capability is demonstrated on 0.65PbFe2/3W1/3O3–0.35PbTiO3 (PFW–PT) ceramics samples for which experimental dependences of the conductivity are measured in a wide temperature range from 20 to 110°C.

A mid-infrared radiometric (MIR) method for precise in situ temperature measurements when studying pyroelectric and electrocaloric properties of bulk and film materials is presented. The method uses new MIR-temperature sensors based on narrowband high-speed and high-sensitive uncooled immersion lens A3B5 photodiodes with a precalibration procedure. They are completely insensitive to the background illumination with λ ≤ 1 µm and provide contactless temperature measurements directly in the area of laser heating action. An accuracy of 50 mK at the temperature around 20 °C, rapidly improving up to 1 mK at 200 °C, is achieved at the operation speed of 1 ms. The reliable and reproducible conditions of measurements of pyroelectric and electrocaloric properties of various samples are formulated, and the novel experimental setup is described in detail. The experimental verification of the method is performed by the measurements of pyroelectric properties of single crystals, bulk ceramics, and AlN film. The results of joint measurements of the pyroelectric and electrocaloric properties of the ferroelectric relaxor ceramics are also presented.

Detection of breakdown voltage and diagnostics of the pre-breakdown state of a material is a topical task of studying the characteristics of dielectric materials and structures on their base under applied external electric field. A new efficient method for diagnosing the pre-breakdown state of multilayer structures (MLC) based on the 0.55PbMg1/3Nb2/3O3-0.45PbSc1/2Nb1/2O3 (PMN-PSN) ferroelectric relaxor is considered. The method is based on the analysis of the dynamics of the MLC surface temperature changes upon application of an external electric field. A set of MLC samples was tested under the action of an electric field E = 10 - 120 kV/cm at temperatures from room temperature to 80 ℃. The critical electric field value characterizing the pre-breakdown state and, consequently, limiting the upper level of operating voltages for electrocaloric applications, was determined for PMN-PSN multilayer structures.

Electrocaloric effect (ECE) as well as field induced pyroelectric and piezoelectric effects were investigated in relaxor ceramics 0.84 PbMg1/3Nb2/3O3–0.14 PbTiO3–0.02 SrTiO3. Dielectric and elastic properties of the solid solution were also studied. To improve the accuracy and reliability of the results obtained, the electrocaloric temperature change δT was measured both by the well-known quasi-adiabatic technique with a contact temperature sensor and by the radiometric mid Infrared technique developed by the authors. The contribution of the secondary pyroelectric effect to the total pyroelectric and ECE was studied in detail. The effect of the induced piezoelectricity on the range of the temperature stability of pyroelectric and electrocaloric responses was shown. The resulting combination of material parameters at reasonable operating temperatures and electric fields, including both the possibility of increasing δT and the existence of its temperature-independent range from 10 to 80 °C, predestines the solid solution as a promising electrocaloric material.

Pyroelectric effect has been studied in quasi-bulk AlN layers with thickness of 10–170 μm produced by hydride–chloride vapor-phase epitaxy on standard Si substrates. The pyroelectric current was measured by the method of sample heating with nonstationary (of the “meander” type) laser light. Combined with the data furnished by independent contactless measurement of the dynamics of the surface temperature of the active layer, this made it possible to determine the pyroelectric coefficient of AlN in a bimorphic AlN/Si structure for various thicknesses of AlN layers. It was found that these values are, on average, smaller than those corresponding to the material produced by the same technology, but on SiC substrates. To obtain comparable pyroelectric coefficients, it is necessary to increase the thickness of the AlN layers by 50–60%. At the same time, the pyroelectric coefficients increased at a large thickness of the AlN layer (110, 170 μm) after the removal of the silicon substrate and reached a value of ~8.6–9.0 μC/(m 2 K).

Electrocaloric and pyroelectric effects of the relaxor 0.55Pb-Mg1/3Nb2/3O3–0.45PbSc1/2Nb1/2O3 (PMN–PSN) bulk and multilayer ceramic (MLC) structures in their connection with the microstructure are reported. The electrocaloric measurements were performed using the mid-infrared radiation (MIR) technique developed and introduced by the authors. The comparison of the electrocaloric temperature change δТ and pyroelectric coefficient p vs temperature dependences of bulk and MLC samples shows a large difference in their temperature behavior. It is shown that significant smearing of these dependences is determined by the microstructure (grain size and grain size distribution) of both bulk and MLC samples. The predicted cooling power of the PMN–PSN MLC can reach Qmax = 1370 mW with reasonable MLC geometry (the number of layers n = 200, the effective length of L = 3.3 mm) and taking into account experimentally obtained δТ = 1.2 °C at a relatively low electric field of 68 kV/cm. Both large values for δТ at ambient temperatures and the estimated cooling power characterize the PMN–PSN MLC as a promising unit for electrocaloric cooling devices.

The determination of the breakdown voltage and the diagnostics of the prebreakdown state of a material is a topical problem of studying characteristics of insulating materials and structures based on them when applying an external electric field. The new effective method of the diagnostics of the prebreakdown state of multilayer structures (MLC) based on the ferroelectric–relaxor 0.55Pb–Mg1/3Nb2/3O3–0.45-PbSc1/2Nb1/2O3 (PMN–PSN) is considered. The method is based on an analysis of the dynamics of changing the MLC surface temperature during applying an external electric field. A series of the MLC samples has been tested under action of electric field E = 10–120 kV/cm and the ambient temperature from room temperature to 80°C. The critical electric field that characterizes the prebreakdown state of the PMN–PSN multilayer structures and, correspondingly, restricts the upper limit of operating voltages for the electrocaloric applications has been determined.

The pyroeffect was studied in quasi-bulk AlN layers with a thickness of 10-170 μm obtained by the technology of chloride-hydride vapor phase epitaxy on standard Si sub-strates. The pyroelectric current was measured by the method of thermal exposure to non-stationary (me-ander type) laser radiation, that together with the data of independent non-contact measure-ment of the active layer surface temperature dynamics made it possible to determine the value of the pyroelectric coefficient AlN in the composition of the bimorph AlN / Si structure for different thicknesses of AlN layers. It was found that the mean values are less than those that correspond to the material obtained by the same technology, but on SiC substrates; so, in or-der to achieve the pyrocoefficients of comparable magnitude with those in the case of “AlN on Si”, an increase in the thickness of AlN layers by 60 -70% is re-quired. At the same time, when the thickness of the AlN layer is large (110 μm, 170 μm) after the removal of the silicon substrate, the pyroelectric coefficient increased and reached ~8.6-9.0μC/(m2·K).