Tourmaline, the first pyroelectric material discovered, is also a promising borosilicate material with non-linear optical and luminescence properties, high thermal stability, high hardness and variable chemical composition. The structural nature of pyroelectricity in tourmaline is a subject of scientific debate since it requires precise structural studies and measurements at elevated temperatures. Here, an in situ high temperature single-crystal and powder X-ray diffraction studies (up to similar to 1000 degrees C) and the direct pyroelectric measurements (up to similar to 200 degrees C) of synthetic Ni, Al-rich tourmaline were performed. The pyroelectric coefficient was calculated from the structural data. The results demonstrate that polyhedra XO9, YO6 and ZO(6) exert the greatest influence on the pyroelectric effect. The pyroelectric coefficient of tourmaline is practically independent of boron-oxygen triangles and silicon-oxygen tetrahedra. The primary pyroelectric coefficient of tourmalines could be calculated from single crystal structural data. This study contributes to the synthesis of tourmalines with the required pyroelectric properties and may be used for the study of the nature and properties of other pyroelectric materials.

DOI: 10.26456/pcascnn/2024.16.219 Abstract: In our work, we used the finely dispersed polystyrene to produce porous samples of the piezoelectric ceramics. Samples of the sodium potassium niobate ceramics with pore concentrations of the 10, 20, 25, 30 and 40 volume percent were produced. The structure was analyzed and the temperature and frequency dependences of the dielectric constant of the obtained samples were investigated. It has been established that the presence of polystyrene in the process of sintering piezoceramic samples plays the role of a binder, which evaporates during high-temperature processing. At the same time, the binder contributes to stabilization of the dielectric properties of the ceramics. In the porous samples, there are no fluctuations of the permittivity in the low-frequency region, and the frequency range in which the permittivity values are independent of the frequency increases. It was found that already 34 volume percent of the pores worsen the mechanical strength of the sample. It is shown that the use of a simple problem of percolation theory does not allow assessing the mechanical strength of porous samples depending on the pore concentration.

In this work, we present the results of our studies of temperature-frequency behaviour of dielectric permittivity epsilon , conductivity a , relaxation time r mu , thermodepolarisation currents j , and pirocurrents gamma in hydrophilic polymers and crystals with a hydrogen-bond network OH...O in the ranges of 0,01-107 Hz and 20-140 degrees & Scy;. Analysis of the obtained data has revealed temperature anomalies of epsilon(T), a(T), r mu(T), j(T), and gamma(T) around << threshold >> points at 20, 36, 50, 65, and 85 degrees & Scy;, where the destruction of water clusters (and, if above 100 degrees & Scy;, of water molecule itself) takes place, and thereby the release of deep traps, the change of the charge carriers (& Ncy;3O+, & Ocy;& Ncy; - , etc.) composition and of their trajectories in volume are observed. In this study, we draw an analogy between the temperature behaviour of epsilon , a , r mu , j , and gamma in << threshold >> points having a characteristic single resonance peak and the dipole resonance of photoabsorption in clusters ofAg, Mg , and Sm metals, which is manifested in the broadening of resonance, single peak splitting, and in the formation of single-domain ATGS+Cr3+ crystal (0,06 wt.% Cr ). We also discuss a possible onset of collective nuclear excitements during irradiation with photons or an onset of internal electrical displacement field E dp in a sudden sample cooling or warming. The entanglement of photons by polarization is also considered.

In this work, ceramic samples with a structure of the type of tetragonal tungsten bronzes, composition Са0.3Ba0.7Nb2O6 (CBN30) pure and with modifying additives SrTiO3, KTaO3 or LiTaO3 (5 mass %) were studied by the oscillographic method. It is shown that the introduction of modifying additives into CBN30 ceramics leads to an increase in the reversal polarization and to a decrease in dielectric losses, both at room temperature and at high temperatures. The introduction of LiTaO3 impurity into the CBN30 composition leads to the greatest increase in the reversal polarization. In contrast to ceramics based on lead zirconate titanate, which have a perovskite type structure, the introduction of SrTiO3 into CBN30 (having the structure of tetragonal tungsten bronzes) does not significantly improve the ferroelectric properties. It has been found that at temperatures above 100 °C for pure CBN30 ceramics, above 165 °C for CBN30 + 5% SrTiO3 and CBN30 + 5% KTaO3, and above 200 оС for CBN30 + 5% LiTaO3, there is a strong increase in dielectric losses. The contribution of dielectric losses to switching processes makes it impossible to determine the temperature of the ferroelectric phase transition for solid solutions based on CBN30 from the temperature dependences of dielectric hysteresis loops.

Comparative studies of low-frequency dispersion, analysis of the most probable relaxation time and activation energy of the low-frequency relaxation process of sodium niobate ceramics obtained under various technological conditions for the synthesis of sodium niobate material were carried out. It is shown that the temperature conditions of the synthesis of the sodium niobate material determine the nature of the low-frequency dispersion only at relatively low temperatures (structural Q or P phase) of sodium niobate samples.

In this work, we obtained at various sintering temperatures and studied the ceramic samples of a 3-component system of barium niobate - calcium - strontium (Ca0,28Ba0,72)(0,25)(Sr0,61Ba0,39)(0,75)Nb2O6 (CSBN25) which is a nanostructured solid solution. The effect of sintering temperature on the structure and dielectric properties of CSBN25 ceramics was studied. It has been established that the CSBN25 sample obtained at a sintering temperature of 1300 degrees C has the optimal ferroelectric properties. For this sample, the pore size does not exceed 10 - 100 nm, while for samples sintered at other temperatures, pores can reach 10 microns. Using examples of CSBN25 ceramics, we have also shown a direct relationship between the uniformity of the grain structure and their packing density with the dielectric properties of the samples: the maximum density and the value of the permittivity have the samples that have a dense, uniform grain structure not only on the surface, but also in the bulk of the samples. Increasing the sintering temperature of CSBN25 ceramics to1350 degrees C leads to the appearance of an amorphous state in the sample bulk and, as a result, to a decrease in the dielectric constant.

In this work, we studied the effect of a modifying additive of finely dispersed polystyrene (2 wt.%) on the dielectric and pyroelectric properties of the ceramic samples Ca0.3Ba0.7Nb2O6 (CBN30) and solid solutions based on it with the addition (5%) of SrTiO3 or LiTaO3, obtained by the solid-phase synthesis method. It is shown that the presence of polystyrene during the sintering of solid solution ceramics based on CBN30 leads to the formation of nanosized pores in the samples and, as a result, leads to a significant decrease in the dielectric losses and a change in the nature of the permittivity dispersion in a wide frequency range of fabricated samples. As a result, the shape of the dispersion diagrams of the ceramics based on CBN30 became similar to the dielectric dispersion of industrial samples of the piezoelectric ceramics of lead zirconate-titanate. The studies of the pyroelectric effect on polarized ceramic samples based on CBN30 revealed that the samples sintered with the presence of polystyrene, in contrast to the samples sintered without polystyrene, have a uniform polarization distribution over the thickness.

In this work, we carried out a comparative study of the surface structure of barium-strontium titanate Ba1-xSrxTiO3 ceramics of various compositions (x = 0,1; 0,2; 0,25; 0,3; 0,4 and 0,5) and the dielectric characteristics of samples in a wide temperature range. It has been found that with increasing the strontium content, a decrease in the density of ceramic samples is observed. An increase in the strontium concentration in the composition of the ceramics under study leads to a reduction in the average grain size by an order of magnitude, and fine grains from 2 mu m to 200 nm. For all ceramic samples of barium-strontium titanate, there is a deviation of the elemental composition from the stoichiometric at the nanoscale. The closest to the stoichiometric composition in terms of the molar content of elements is the composition of the Ba0,75Sr0,25TiO3 samples. It was found that the samples of this composition have the highest value of the permittivity at room temperature. Temperature studies of the dielectric permittivity showed the existence of two maxima: at a temperature of 130 degrees C, corresponding to the Curie temperature of pure barium titanate ceramics, and at lower temperatures in the range from 10 to 100 degrees C, the second depends on the strontium content. The low-temperature maximum for the epsilon value corresponds to the diffuse transition of the solid solution Ba1-xSrxTiO3, whose relaxor properties are confirmed by deviation of the temperature dependence from the Curie-Weiss law. The samples of Ba0,75Sr0,25TiO3 composition have the most pronounced relaxor behavior.

We have analyzed the complex permittivity of a porous (10 volume % of pores) sodium-lithium niobate ceramic with the results of computer simulation. The calculation was based on the Cole-Cole formula, which took into account the presence of various mechanisms of relaxation processes in the low-frequency (linear dispersion) and mid-frequency regions, an additional term from the Debye formula was added to take into account the mixed polarization, and a term taking into account the damping factor was added for resonant-type polarization. The simulation was carried out with and without the conductivity taken into account. To take into account the contribution of conductivity to the dynamic dielectric response, the expression sigma* = (epsilon '' + i epsilon ')epsilon(0)omega was used. It is shown that the linear part of the frequency dependence in the range from 50 Hz to 1 MHz is equally well described both with and without conductivity. At the same time, the behavior of the dielectric response of piezoelectric ceramics in the high-frequency region, where resonance effects are observed, and the low-frequency region, where volume-charge polarization predominates, is much better described taking into account the contribution of conductivity to the dielectric response of the system.

As a result of comparative studies of the electric and dielectric properties of sodium-lithium niobate ceramics with a percentage of Li equal to 10 and 40 mass %, it was found that both materials have a hopping conduction mechanism. At frequencies from 500 Hz to 100 kHz, thermal ionic polarization predominates. In the low-frequency region, migratory polarization predominates. The revealed difference in the temperature behavior of the complex conductivity of the studied samples made it possible to explain the presence of ferroelectric properties in the sample with 10% Li and their absence in the sample with 40% Li.

В работе методом твердофазного синтеза получены образцы керамики состава CaBaNbO чистого и с модифицирующими добавками (5%) SrTiO, KTaO или LiTaO. У всех исследуемых составов керамик выявлено наличие крупных и мелких зерен. Показано, что вхождение LiTaO в состав керамики CaBaNbO на порядок уменьшает размер зерен, а вхождение SrTiO приводит к удлинению формы зерна. На основе анализа элементного состава установлено, что введение модификаторов в состав CaBaNbOуменьшает избыток кислорода в структуре тетрагональной вольфрамовой бронзы, по сравнению с немодифицированной керамикой CaBaNbO. Максимум на температурной зависимости диэлектрической проницаемости практически не зависит от типа модификатора и лежит в интервале 279-285°С. Это на 60 градусов выше температуры Кюри монокристалла CaBaNbO. Независимо от температуры измерения, максимальное значение диэлектрической проницаемости имеет материал CaBaNbOO + 5%SrTiO. Тогда как минимальное значение диэлектрической проницаемости при комнатной температуре имеет образец CaBaNbO + 5%LiTaO, а в точке Кюри - образец CaBaNbO. In this work, the ceramic samples CaBaNbO pure and with modifying additives (5%) SrTiO, KTaO or LiTaO were obtained by solid-phase synthesis. All studied compositions of ceramics revealed the presence of large and small grains. It is shown that the addition of LiTa0 to the composition of CaBaNbO ceramics reduces the grain size by an order of magnitude, while the addition of SrTi0 leads to an elongation of the grain shape. Based on the analysis of the elemental composition, it was found that the introduction of modifiers into the composition of CaBaNbO reduces the excess of oxygen in the structure of tetragonal tungsten bronze, compared to unmodified CaBaNbO ceramics. The maximum on the temperature dependence of the permittivity is practically independent of the type of modifier and is located in the range of 279-285°C. This is 60 degrees higher than the Curie temperature of the CaBaNbO single crystal. Regardless of the measurement temperature, CaBaNbO + 5%SrTiO material has the maximum value of the permittivity. Whereas the minimum value of the permittivity at room temperature has the CaBaNbO + 5%LiTa0 sample, and at the Curie point, the CaBaNbO sample.

В работе представлены результаты исследования влияния постоянного магнитного поля на дисперсию комплексной диэлектрической проницаемости слоистого композита (связность 2-2) на основе титаната бария - феррита бария. Показано, что при изготовлении магнитоэлектрического композита титанат бария -феррит бария со связность 2-2 появляется сильная диффузия железа в слой керамики титаната бария на границе раздела двух материалов. Обнаружено, что железо проникает равномерно, со случайными отклонениями и экспоненциального спада по мере вхождения железа в титанат бария не наблюдается. Установлено, что постоянное магнитное поле не влияет на диэлектрические характеристики в переменном электрическом поле на частотах выше 1600 Гц. При более низких частотах, отжиг в параэлектрической фазе увеличивает сопротивление образца, а последующее воздействие постоянного магнитного поля приводит к его уменьшению. Выявлено, что изменение типа связности магнитоэлектрического композита от 0-3 к 2-2 добавляет дополнительные, более мелкие, резонансные и антирезонансные пики при исследовании пьезоэлектрических свойств методом резонанса - антирезонанса. При этом образцы имеют достаточные для практического применения величины пьезоэлектрического модуля (d > 40⋅10 Кл/Н; d > 120⋅10 Кл/Н). The paper presents the results of a study of the influence of a constant magnetic field on the dispersion of the complex permittivity of a layered composite (connectivity 2-2) based on barium titanate - barium ferrite. It is shown that in the manufacture of a magnetoelectric composite of barium titanate - barium ferrite with a connectivity of 2-2, a strong diffusion of iron appears into the barium titanate ceramic layer at the interface between the two materials. It was found that iron penetrates evenly, with random deviations, and no exponential decline as iron enters into barium titanate is observed. It has been established that a constant magnetic field does not affect the dielectric characteristics in an alternating electric field at frequencies above 1600 Hz. At lower frequencies, annealing in the paraelectric phase increases the resistance of the sample, and subsequent exposure to a constant magnetic field leads to its decrease. It was revealed that changing the type of connectivity of the magnetoelectric composite from 0-3 to 2-2 adds additional, smaller, resonance and antiresonance peaks in the study of piezoelectric properties by the resonance-antiresonance method. At the same time, the samples have sufficient values of the piezoelectric modulus for practical application (d > 40⋅10 C/N; d > 120⋅10 C/N).

Comparative studies of the temperature dependences and dispersion of the complex permittivity of sodium niobate and sodium-lithium niobate ceramics have been carried out. It is shown that the structural transition to the R phase (370°C) of sodium niobate ceramics is a ferroelectric phase transition. For sodium niobate ceramics, the existence of three fundamentally different mechanisms of relaxation processes has been established: classical (Debye type), linear, and relaxation (elastic ionic), the existence of which is determined by the structural phase. The addition of 10% lithium niobate to the sodium niobate ceramics not only increases the temperature of the structural phase transition, but also eliminates the mechanisms for the occurrence of relaxation polarization.

Using the method of solid-phase synthesis, we obtained ceramic samples with a structure like tetragonal tungsten bronzes, pure Ca 0.3 Ba 0.7 Nb 2 O 6 (CBN30) and with modifying additives SrTiO 3 , KTaO 3 , or LiTaO 3 . The dispersion of the permittivity in the frequency range from 1 Hz to 10 MHz, the temperature dependences of the permittivity (in the given frequency range) and the pyroelectric coefficient are studied. It is shown that if the introduction of the LiTaO 3 impurity into the composition of CBN30 destabilizes the dielectric characteristics at frequencies above 100 kHz, then the SrTiO 3 impurity increases both the permittivity and the pyroelectric coefficient, significantly reducing dielectric losses at low (1-10 Hz) frequencies. At the same time, both of these impurities (SrTiO 3 and LiTaO 3 ) lead to sample depolarization during heating above 150 o C, while the KTaO 3 impurity, which slightly increases the permittivity and pyroelectric coefficient, does not affect the stability of the polarized state during heating up to higher temperatures. Keywords: piezoelectric ceramics, barium-calcium niobate, lead-free materials, permittivity dispersion, pyroelectric effect.

Comparative studies of the pyroelectric properties and structural features of sodium niobate and sodium-potassium niobate ceramics obtained under different technological conditions for the synthesis of sodium niobate have been carried out. X-ray phase analysis revealed the existence of an additional phase with the chemical formula NaNb10O18 in sodium niobate ceramic samples that do not exhibit ferroelectric properties. It is shown that the temperature conditions for the synthesis of the sodium niobate material determine the nature of the macroscopic polarization of the samples of both pure sodium niobate and sodium-potassium niobate. Keywords: piezoelectric ceramics, lead-free materials, polarization, pyroelectric effect.