The paper studies ceramic samples prepared using traditional ceramic technology also knows as conventional sintering. Samples were prepared from Eu3+ activated fine powders of gadolinium niobate-tantalates GdNb1−yTayO4 (y = 0, 0.7, 1); Eu3+ concentration was x = 0.01, 0.2 and 0.4. Powders were synthesized using nitrate solutions Gd and Eu and niobium and tantalum hydroxides. The hydroxides were coprecipitated from hydrofluoric acid solutions. Full-profile analysis (Rietveld refinement) of XRD (X-ray diffraction) patterns of polycrystals determined the phase composition and refined the parameters of the structure of solid solution phases depending on the Eu concentration. Morphological features of the microstructure have been studied for gadolinium niobate-tantalate ceramics Gd1−xEuxNb1−yTayO4 where y = 0, 0.7, 1 and x = 0.01, 0.2, 0.4. Their mechanical properties have been studied; strength characteristics (Young’s modulus, microhardness) and critical stress intensity factor for mode I KIC have been estimated. The compositions and modes for producing ceramics with optimal mechanical properties have been determined. The photoluminescence (PL) has been studied in ceramic solid solutions in the visible range upon excitation by near UV (376 nm). The features of energy transfer between the host of ceramic GdNb1−yTayO4:Eu solid solution (y = 0; 0.7; 1) and 4fn-4fn levels of Eu in concentrations x = 0.01, 0.2 and 0.4 have been established. We have established that concentration quenching of PL in single-phase ceramics Gd1−xEuxNbO4 occurs above Eu concentration x > 0.01 and in ceramics Gd1−xEuxTaO4—at Eu concentration x > 0.2. The sample with the composition Gd0.99Eu0.01NbO4 demonstrated the maximal PL intensity among all other studied samples. The least PL intensity is observed in Gd0.99Eu0.01Nb0.3Ta0.7O4 relative to individual compounds of gadolinium niobates and tantalates, activated with Eu in the same concentration x = 0.01. The significant difference in Stark splitting of levels has been shown for solid solutions based on niobium (Gd1−xEuxNbO4) and tantalum (Gd1−xEuxTaO4). The compositions of ceramic GdNb1−yTayO4:Eu solid solution have been established which have maximum luminance. We have determined that the luminance of some of the studied samples exceeded the luminance of an industrial phosphor based on Y2O3:Eu3+.

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.

Fine powders of yttrium orthoniobate activated by Eu, Sm, Tb, Er have been synthesized by the sol-gel. The synthesized powders have been calcined at different temperatures (1000, 1100 and 1180 degrees C). Luminescent ceramics (Y0.96 & IEcy;u0.01Sm0.01Tb0.01Er0.01)NbO4 were prepared from fine powders by uniaxial hot pressing (UHP) via various technological modes. For the first time, the crystal structure, microstructure, spectral composition, photoluminescence properties of (Y0.96 & IEcy;u0.01Sm0.01Tb0.01Er0.01)NbO4 ceramics have been studied depending on the temperature conditions of the synthesis of powders and UHP conditions during sintering of ceramics. The mechanical properties of these ceramics (Young's modulus, microhardness and critical stress intensity factor for the mode I KIC) have been evaluated.

We have obtained for the first time ferroelectric solid solutions (i.e. ceramic) Li0.12Na0.88TayNb1-yO3 (y = 0.15, 0.2, 0.25) with the perovskite structure under conditions of high pressures and temperatures. Their electrophysical characteristics have been studied. It has been established that the solid solutions ceramic samples have an orderly distorted crystal structure. The values of static specific conductivities have been determined as functions of temperature, the activation energy of charge carriers, and the real part of the permittivity. It has been established that the samples experience a number of successive phase transitions. For example, P -* R -* S (T2). It has been found that the electrical conductivity increases when the content of tantalum increases. The Li0.12Na0.88Ta0.25Nb0.75O3 ceramic sample has atypically high electrical conductivity values (close to high ionic conductivity) for this class of solid solutions over the entire studied temperature range. At the same time, the phase is metastable, and heating above the Curie temperature leads to its gradual destruction.

We have found approaches to the synthesis of cheap near-stoichiometric lithium nickelate (LiNiO2). The resulting phases have been identified by X-ray phase analysis. Obtained materials have been studied by spectrometric method; electron microscopy; BET method; impedance spectroscopy. A technological scheme has been developed, the optimal conditions for the combined synthesis of lithium nickelate close to the stoichiometric composition Li0.98Ni1.02O2 have been determined. We have proved that nanosized samples with a well-developed surface form during such a synthesis. We have determined that the electrochemical characteristics of the samples correspond to those of lithium nickelate used in commercial electrochemical cells.

Ceramic samples of polycomponent solid solution (Y0.96Eu0.01Sm0.01Tb0.01Er0.01)Nb0.7Ta0.3O4 have been prepared by sol–gel synthesis from fine powders obtained using nitrate solutions of rare earth elements REE and coprecipitated hydroxides of niobium and tantalum. The structural state of the initial powders’ crystal lattice has been investigated. The morphological features of the microstructure of the ceramics samples have been studied in dependence of temperature regimes of their preparation. The ceramics’ strength characteristics (Young’s modulus) and the critical stress intensity factor of the mode I KIC have been estimated. Cathode- and photoluminescent properties of ceramic solid solutions (Y0.96Eu0.01Sm0.01Tb0.01Er0.01)Nb0.7Ta0.3O4 have been studied.

Ceramic samples of polycomponent solid solutions (SSs) Na0.90K0.05Cd0.05NbO3 (Cd-modified KNN) and [(Na0.90K0.05Cd0.05)0.95REE0.05]NbO3, where REE = La, Pr, Tb, Dy, Ho, were obtained by the uniaxial hot pressing (UHP) method. The crystal lattice structures, morphological features of the microstructure, and dielectric and thermophysical properties of these ceramics have been investigated. For the first time, their strength characteristics (Young’s modulus) and the critical stress intensity factor of the mode I Kic have been estimated. Photoluminescent properties have been compared in SSs [(Na0.90K0.05Cd0.05)0.95REE0.05]NbO3 in the visible wavelength range.

In the work, a fine powder of GdNb0.9Ta0.1O4-mixed gadolinium tantalum niobate activated with rare earth (REE) cations (Sm3+, Eu3+, Tb3+ and Er3+) was obtained by sol–gel synthesis. The evolution of the powder from amorphous to crystalline form was also studied in the work. The evolution was studied by synchronous thermal and X-ray analysis. The phase composition and structure of the resulting Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 powders were analyzed in detail. Ceramic samples of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 polycomponent solid solution were prepared from the sol–gel synthesized powder using traditional ceramic technology. The phase composition and characteristics of the structure of individual phases of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic solid solution was determined by full-profile analysis of XRD patterns of polycrystals. We established that incorporation of REE (Tb, Er, Eu, Sm) into the gadolinium site in GdNb0.9Ta0.1O4 solid solution leads to various distortions of the corresponding polyhedra. Note that the distortion degree in this case is much greater than the distortion of the initial GdNbO4 structure. The photoluminescent (PL) properties of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 solid solution were studied in the visible wavelength range. Analysis of literature and our own data revealed: electronic relaxation pathways in Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics can be different depending on the energy of the exciting radiation. Excitation by the 376 nm line leads to internal energy conversion over 4fn–4fn levels of REE cations (Sm3+, Eu3+, Tb3+ and Er3+). The energy transfer between the Nb4+–O−–Ta4+–O− groups and REE is maximal in this case, while the radiation of the matrix from Nb4+–O−–Ta4+–O− emission centers is minimal. Upon excitation in the near-UV range (376 nm), Gd3+ cations do not participate in the energy transfer between the matrix and 4fn–4fn levels of REE dopants. The maximum PL of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics is observed in the green–red region of the spectrum from 5D0–7F2 and 4G5/2–6H7/2 transitions of Eu3+ and Sm3+. The emission is maximal at 612 nm; it corresponds to the 5D0–7F2 electric dipole transition of the Eu3+ cation. We established that the efficiency of energy transfer between the matrix and doping REE cations for Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics strongly depends on the energy of the exciting radiation.

We have found approaches to the synthesis of cheap near-stoichiometric lithium nickelate (LiNiO2). The resulting phases have been identified by X-ray phase analysis. Obtained materials have been studied by spectrometric method; electron microscopy; BET method; impedance spectroscopy. A technological scheme has been developed, the optimal conditions for the combined synthesis of lithium nickelate close to the stoichiometric composition Li0.98Ni1.02О2 have been determined. We have proved that nanosized samples with a well-developed surface form during such a synthesis. We have determined that the electrochemical characteristics of the samples correspond to those of lithium nickelate used in commercial electrochemical cells.Keywords: Lithium-ion batteriessol-gelsolid-state synthesiselectrochemical propertieslithium nickelate AcknowledgmentsAuthors appreciate help with preparation of the manuscript from Andrey Novikov, Anna Shirokaya, Vasiliy Semushin, Anastasiya Kniazeva from Tananaev Institute of Chemistry (ICT RAS).Disclosure statementNo potential conflict of interest was reported by the authors.Additional informationFundingThis research was funded by the Ministry of Science and Higher Education Russian Federation scientific topic 0186-2022-0002 (registration # FMEZ-2022-0016) and 0186-2022-0009 (registration # FMEZ 2022-0015).

Results on the synthesis of lithium-conducting ceramics Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 by the method of spark plasma sintering (SPS) are presented. In the first stage, the monophase Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 solid-electrolyte powder is synthesized from the nitrate-peroxide precursor. Its subsequent consolidation by the SPS method provides the formation of ceramics with the high Li-ionic conductivity and the density on the level of 97–98%. The microstructure and the electrochemical properties of the Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 ceramics are studied.

The temperature dependences of the complex permittivity and the dielectric loss tangent of ferroelectric solid solutions Li0.03Na0.97TayNb1–yO3 (y = 0.1–0.7) with the perovskite structure have been studied. It has been found that Li0.03Na0.97TayNb1–yO3 solid solutions undergo three phase transitions in the studied temperature range. The temperatures of ferroelectric phase transitions have been determined, and it has been established that an increase in the tantalum concentration leads to a decrease in this temperature. It is revealed that the studied solid solutions at room temperature have high values of εʹ in the low frequency region.

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.

We have studied the electrical conductivity and mechanical characteristics of a Li7 – 3хAlхLa3Zr2O12 solid electrolyte with the garnet structure. Its ionic conductivity has been determined using electrochemical impedance spectroscopy in the frequency range 10 Hz to 2 MHz, and its electronic conductivity has been evaluated using potentiostatic chronoammetry. The total ionic conductivity of Li7 – 3хAlхLa3Zr2O12 is 1.8 × 10–4 S/cm, and its electronic conductivity does not exceed 2.7 × 10–9 S/cm. The elastic and mechanical properties of Li7 – 3хAlхLa3Zr2O12 ceramics have been studied by a contact method using a Nanoskan probe microscope/nanohardness tester. We present microhardness data obtained by comparative scratch testing and Young’s modulus evaluated from cantilever approach curves.

Fine powders of mixed gadolinium tantalum niobates doped with Eu, Sm, Tb, and Er were synthesized. Ceramic samples of polycomponent solid solutions of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 were obtained from synthesized powders using conventional sintering technology. The phase composition and phase structure characteristics of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic phases were determined by XRD. The effect of ceramic sintering temperature on the physical characteristics of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 solid solutions is shown. The morphological features of the microstructure of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics were studied in relation to its mechanical characteristics. At the same time, the strength characteristics (Young's modulus, microhardness) and the critical stress intensity factor for mode I K-IC were evaluated for the first time for the synthesized compounds. Photoluminescence and cathodoluminescence were studied in the visible region. The study confirms the potential application of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic solid solutions as scintillators and radioluminescent light sources.

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.

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.

The electrochemical and mechanical characteristics of ceramic solid electrolytes Li1 +xAlxTi(Ge)2– x(PO4)3 with the high Li-ionic conductivity and the NASICON crystal structure are considered. The ionic conductivity of solid electrolytes is studied by the method of electrochemical impedance spectroscopy in the frequency interval from 10 to 2 × 106 Hz. The transfer numbers of Li+ ions and the electronic conductivity are determined by potentiostatic chronoamperometry. The elastic and mechanical properties of ceramics are studied by the contact method by means of a probe microscope-nanohardness tester Nanoskan. The microhardness data obtained by comparable sclerometry and Young’s modulus determined based on cantilever approach curves are shown. The critical stress intensity factor for stresses of the first kind KIC is determined for ceramic solid electrolytes Li1 +xAlxTi(Ge)2– x(PO4)3.

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.