The electrophysical properties (dielectric permittivity, dielectric loss tangent, electrical conductivity) of Li0.03Na0.97TayNb1-yO3 (у = 0.1 – 0.7) ferroelectric solid solutions with the perovskite structure were studied. In the temperature range of 290 – 830 K, the investigated solid solutions undergo three phase transitions. The phase transitions are strongly smeared as the tantalum concentration increases. The Curie temperatures are established and it is shown that an increase in the concentration of tantalum leads to a decrease in this temperature. The values of the static electrical conductivity of ferroelectric solid solutions Li0.03Na0.97TayNb1 – yO3 (у = 0.1 – 0.7) and the activation enthalpies of charge carriers are determined.

We have established optimized parameters of technological process for obtaining of translucent luminescent YNbO4 ceramics by uniaxial hot pressing (UHP). Ultrafine crystalline powders used for this have been synthesized by sol-gel and sintered at three different temperatures. Series of ceramic YNbO4 samples were obtained from the powders by UHP at three different sintering conditions. Morphological features of the microstructure, mechanical and photoluminescent characteristics in the visible wavelength range have been compared for YNbO4 ceramic samples obtained at different UHP conditions and controlled with sample prepared by conventional sintering (CS). The most optimal UHP regime for translucent YNbO4 ceramics obtaining have been chosen.

A series of mixed yttrium tantalo-niobates (YNbхTa1–хO4, x = 0-1) is obtained by the sol-gel synthesis. It is shown that the temperature of this synthesis of YNbхTa1–хO4 and its duration are much lower than those in the solid-phase synthesis. The properties of both synthesized powders and ceramic solid solutions (SSs) YNbхTa1–хO4, x = 0-1, prepared based on them, are investigated. It is found that under UV excitation at any Nb:Ta ratio in YNbхTa1–хO4 SSs the luminescent signal is enhanced as compared to that in individual YNbO4 and YTaO4 compounds, which is caused by energy transfer between the Nb4+–O– and Ta4+–O– luminescence centers. Morphological features of the microstructure of ceramic YNbхTa1–хO4 SSs are studied. Mechanical characteristics of ceramic YNbхTa1–хO4 SSs, such as Young’s modulus and the stress intensity factor for mode 1 KIC, which is a criterion of the material crack resistance, are estimated.

We study the process of meteoroid interaction with the Earth's atmosphere, in particular, the effect of ablation.An ablation model is used, where mass loss of a meteoroid is determined using the saturated vapor pressure of the assumed meteoroid's substance.An automated method is suggested, where we estimate the physical parameters of a meteoroid by comparing data from observations and models of known parameters.Model constraints and features of the models are discussed.

Fine crystalline GdNbO4 powders have been synthesized by sol-gel method. Usual ceramic technology and hot pressing have been applied to obtain GdNbO4 ceramic samples. Morphological particularities have been studied in GdNbO4 ceramics microstructure. Ceramics strength characteristics (strength, Young’s modulus) have been evaluated for the first time. A mode I stress intensity factor KIC have been determined (note that the factor is a crack resistance criterion). Photoluminescence characteristics have been compared in GdNbO4 ceramics before and after vacuum annealing in the visible region.

Lithium cobaltate with stoichiometric composition (LiCoO2) is synthesized by the sol–gel method. The physical parameters (particle size, specific surface area, and specific static conductivity) of studied samples are found and their dependence on the calcination temperature is revealed. The following three conduction mechanisms are shown to contribute to the conductivity value: frequency-independent σ0, ionic transport in the sample bulk σsv, and ionic transport at the electrode/ionic conductor interface σdl. The optimal modes of thermal treatment that allow the highly developed specific surface of LiCoO2 to be retained are determined.

Представлены результаты исследования сегнетоэлектрического твердого раствора LiNaTaNbO со структурой перовскита, основанного на ниобате натрия и синтезированного в условиях высокого давления и температуры. Методом импеданс спектроскопии в области температур 290 - 800 К были определены значения удельных проводимостей на постоянном токе, энергии активации носителей заряда и реальная часть диэлектрической проницаемости. Показана эволюция температурных аномалий удельной проводимости и диэлектрической проницаемости при термоциклировании. Обнаруженые эффекты связанны со структурными фазовыми переходами, определена температура Кюри. LiNaTaNbOпретерпевает фазовый переход второго рода. Установлено, что в LiNaTaNbO образуется метастабильная фаза, обладающая высокой электропроводностью в области комнатной температуры. При нагреве выше температуры Кюри данная фаза разрушается. Обсуждаются возможные механизмы обнаруженных явлений. The results are presented of a study of a ferroelectric solid solution LiNaTaNbO with a perovskite structure based on sodium niobate and synthesized under high pressure and temperature. In the temperature range of 290-800 K, the values of the specific conductivity at direct current, the activation energy of charge carriers, and the real part of the dielectric constant were determined by the method of impedance spectroscopy. Evolution of temperature anomalies of specific conductivity and dielectric constant during thermal cycling is shown. The observed effects are associated with structural phase transitions, and the Curie temperature is determined. The LiNaTaNbO undergoes a second-order phase transition. It was found that a metastable phase is formed in LiNaTaNbO, which has a high electrical conductivity at the room temperature. When heated above the Curie temperature, this phase is destroyed. Possible mechanisms of the discovered phenomena are discussed.

Методом золь-гель синтеза получена серия смешанных танталониобатов иттрия (YNbхTa1–хO4, x = 0—1). Показано, что температура для такого получения YNbхTa1–хO4 и время синтеза существенно меньше, чем для твердофазного синтеза. Исследованы свойства как синтезированных порошков, так и керамических твердых растворов (ТР) YNbхTa1–хO4, x = 0—1, приготовленных на их основе. Установлено, что под действием возбуждающего УФ излучения в ТР YNbхTa1–хO4 при любом отношении Nb:Ta происходит усиление люминесцентного сигнала относительно индивидуальных соединений YNbO4 и YTaO4, что обусловлено передачей энергии между центрами свечения Nb4+—O– и Ta4+—O–. Исследованы морфологические особенности микроструктуры керамических ТР YNbхTa1–хO4. Оценены механические характеристики керамических ТР YNbхTa1–хO4, такие как модуль Юнга и критический коэффициент интенсивности напряжений первого рода KIC, являющийся критерием трещиностойкости материала.

Ferroelectric ceramic Li x Na 1 – x Ta y Nb 1 – y O 3 ( x = 0 . 17, y = 0 – 0 . 5) solid solutions with perovskite structure are synthesized for the first time by the thermobaric synthesis method (6 GPa, 1400–1800 K). The features of their structure and elastic properties are studied. It is shown that ceramic samples consist of grains of isomorphic shape and that faceting is inherent in the perovskite structure, allowing the coexistence of the rhombic phase of different symmetries of the P 21 ma and Pbcm unit cell. An increase in the synthesis temperature leads to a decrease in the Young’s modulus. The dispersion of the permittivity and its temperature dependence are studied. Specific static values of electrical conductivity and their temperature dependence, as well as the most probable relaxation time, are determined. Carrier activation enthalpies H a and transport enthalpy H m are calculated. It is established that the studied ceramic samples undergo a ferroelectric phase transition, while an increase in tantalum concentration lowers the Curie temperature. Li 0 . 17 Na 0 . 83 Та 0 . 1 Nb 0 . 9 O 3 in the paraelectric phase is found to be a superionic conductor.

LiTaO3 ceramics has been produced from a fine powder synthesized by a sol-gel method from a Li,Ta-containing citrate precursor, and its microstructure and mechanical and electrical properties have been studied. Young’s modulus and microhardness of the ceramic lithium tantalite have been determined. The critical stress intensity factor of mode I KIC, which is a criterion for the crack resistance of a material, has been evaluated, and the effective fracture energy of the LiTaO3 ceramics has been determined. The complex impedance dispersion Z*(ω) has been studied, and temperature dependences of dielectric constant and conductivity have been measured in the temperature range ~300–705 K, which is crucial for the acoustoelectronic applications of ceramic lithium tantalate. In the temperature range studied, the static conductivity and relaxation time of LiTaO3 ceramics have been determined. The charge transport activation enthalpies for various temperature ranges have been estimated.

Методом термобарического синтеза (6 GPa, 1400-1800 K) впервые синтезированы сегнетоэлектрические керамические твердые растворы LixNa1-xTayNb1-yO3 (x=0.17, у=0-0.5) со структурой перовскита. Исследованы особенности их микроструктуры и упругих свойств. Показано, что керамические образцы состоят в основном из зерен изоморфной формы, огранка присуща перовскитной структуре, допускающей сосуществование ромбической фазы разной симметрии P21ma и Pbcm элементарной ячейки. Увеличение температуры синтеза привело к уменьшению величины модуля Юнга. Исследована дисперсия диэлектрической проницаемости и ее температурная зависимость. Определены удельные статические значения электропроводности и их температурная зависимость, наиболее вероятные времена релаксации и рассчитаны энтальпии активации носителей заряда Ha и транспортная энтальпия Hm. Установлено, что исследуемые керамические образцы претерпевают сегнетоэлектрический фазовый переход, при этом увеличение концентрации тантала понижает температуру Кюри. Обнаружено, что Li0.17Na0.83Та0.1Nb0.9O3 в параэлектрической фазе является супериоником. Ключевые слова: ниобат натрия, сегнетоэлектрик, модуль Юнга, импеданс спектроскопия, фазовый переход.

Ceramic solid solutions GdNbx[Formula: see text]O4 ([Formula: see text]–1) were synthesized by sol–gel. Morphological particularities of microstructure were studied, strength characteristics (Young’s modulus) and stress intensity factor for mode I [Formula: see text] were evaluated. The latter is a criterion of crack resistance of the material. Luminescent properties of solid solutions GdNbx[Formula: see text]O4 were researched under UV exciting radiation. A comparatively small addition of Ta ([Formula: see text]) was shown to increase luminescence intensities of centers [Formula: see text]–O−. An addition of Ta to GdNbO4 leads to creation of solid solution [Formula: see text][Formula: see text]O4. Intensity of these centers is 3–6.5 times larger than that of GdNbO4 and GdTaO4.

Ferroelectric ceramic LixNa1 –xTayNb1 –yO3 (x = 0.17, y = 0–0.5) solid solutions with perovskite structure are synthesized for the first time by the thermobaric synthesis method (6 GPa, 1400–1800 K). The features of their structure and elastic properties are studied. It is shown that ceramic samples consist of grains of isomorphic shape and that faceting is inherent in the perovskite structure, allowing the coexistence of the rhombic phase of different symmetries of the P21ma and Pbcm unit cell. An increase in the synthesis temperature leads to a decrease in the Young’s modulus. The dispersion of the permittivity and its temperature dependence are studied. Specific static values of electrical conductivity and their temperature dependence, as well as the most probable relaxation time, are determined. Carrier activation enthalpies Ha and transport enthalpy Hm are calculated. It is established that the studied ceramic samples undergo a ferroelectric phase transition, while an increase in tantalum concentration lowers the Curie temperature. Li0.17Na0.83Та0.1Nb0.9O3 in the paraelectric phase is found to be a superionic conductor.

A ferroelectric solid solution Li0,12Na0,88Ta0,25Nb0,75O3 with a perovskite structure, synthesized under the high pressure and temperature conditions, has been studied by impedance spectroscopy in the temperature range 290 - 460 K. The values of static conductivity, the most probable relaxation times as functions of temperature, the activation enthalpy of charge carriers, and the real part of the dielectric constant have been determined. It was found that at room temperature Li0,12Na0,88Ta0,25Nb0,75O3 has a high electrical conductivity, close to the superionic one. Possible mechanisms of the discovered phenomenon are discussed.

The microstructure of ceramic lithium tantalite LiTaO3, obtained on the basis of finely dispersed microcrystalline monophasic powder, was studied by the probe microscopy. A comparative study of the dispersion of the complex impedance Z* (omega) of LiTaO3 and a crystalline sample of a non-polar X - orientation slice, grown by the Czochralski method, was carried out. Using measured Z and phi values, the real and imaginary components of the complex dielectric constant and impedance (admittance) are determined.

— The electrical properties and phase states of Li 0.17 Na 0.83 Nb у Та 1 – у O 3 ( y = 0.1–0.5) ferroelectric perovskite solid solutions prepared by high-pressure, high-temperature synthesis have been studied using impedance spectroscopy. The ε'( T ) and σ sv ( T ) curves of the solid solutions have been shown to have anomalies due to phase transitions of the materials. Their Curie temperature has been found to decrease with increasing Ta concentration. The static electrical conductivity of the solid solutions has been measured as a function of temperature and the enthalpies of activation of charge carriers in them have been evaluated. The Li 0.17 Na 0.83 Nb 0.1 Та 0.9 O 3 solid solution has been shown to be a high-temperature superionic conductor. Possible mechanisms of the observed phenomena are discussed.

The manufacture of LiNbO3 and LiNbO3:Zn fine-grained powders by two variants of the sol–gel process was studied. The microstructure, mechanical and electric properties of LiNbO3 and LiNbO3:Zn ceramics prepared from powders of various origins were studied. The ceramics prepared from powders that had been fractionated by elutriation had uniform micro- and submicrostructure, improved strength characteristics, and ionic grain-boundary conductivity. Doping LiNbO3 with Zn2+ reduced the electronic conductivity of LiNbO3:Zn ceramics, and this allowed the ceramics to be efficiently polarized and their piezoelectric properties to be improved.