Growth of solid solutions of intermediate compositions of LiNb1–xTaxO3 (lithium niobate tantalate, LNT) crystals allows us to adjust the physical parameters of the material and obtain crystals with the required properties, which is why obtaining such crystals and studying their properties taking into account anisotropy is an urgent task. Crystals of solid solutions of LNT composed of LiNb0.88Ta0.12O3 and LiNb0.93Ta0.07O3 are grown in this study. Polished samples oriented in the standard installation were prepared from these crystals. The samples are subjected to monodomenization. The polarity of the piezoactive faces is determined. By optical microscopy in transmitted light, patterns in the form of a sponge-like structure are observed on all samples of Z-cuts, patterns in the form of vertical regions parallel to the optical axis (Z axis) are observed on samples of X- and Y-cuts. Taking into account anisotropy and polarity, measurements of the mechanical characteristics of the samples at a load of 25 Gs are carried out: the microhardness of the samples according to the Vickers hardness (HV) calculated on the Mohs scale HM and the brittleness score Zx. According to the obtained data, the parameters of the viscosity S according to the Palmquist method and the degree of ionic bonds are calculated. The effect of the Nb : Ta ratio on the microhardness of Z-cuts is ambiguous, this may be due to the significant heterogeneity of such samples. In the case of X-cut samples, the results of microhardness measurements are close to each other and within the error limits of the method. In the case of Y-cuts, there is a significant difference in the values of microhardness and brittleness of Y+ and Y– sections, while the microhardness of the sample with a higher Nb content is higher.

A large number of modern functional single crystals of the middle category belong to gyrotropic media. In these crystals, when light propagates along the optical axis, rotation of the plane of its polarization is observed. In this study a spectrophotometric method is used to obtain the dispersion dependences of the rotation angle of the polarization plane. This method is based on measuring the intensity of the light passing through the polarizer–crystal–analyzer system. The crystal is a polished plane-parallel plate of a uniaxial gyrotropic crystal cut perpendicularly to the optical axis. Measurements are carried out on a Cary-5000 UV-Vis-NIR spectrophotometer in the wavelength range of 200–1200 nm using polarizers Glan–Taylor prisms. Polished plane-parallel plates of known SiO2 and α-LiIO3 crystals are used as samples. The obtained dispersion dependences of the spectral transmission coefficients have an oscillating character. The discrete values of the specific angles of rotation of the plane of polarization of light are calculated from the extrema on these dependences. These discrete values can be approximated by the Drude, Chandrasekhar, and Vyshin formulas, depending on what determines the nature of the rotational ability of the plane of polarization of light in each particular material. For the studied crystals the dependences of the modified Drude formula of the form 1/ρ = f(λ2), which should have a linear character in the case of an ideal crystal, are plotted. The obtained experimental results are closely correlated to the available published data. The advantages of this method lie in its efficiency, the possibility of obtaining dispersion dependences of the specific rotation angle of the polarization plane, the need for a single sample, the possibility of assessing the nature of the rotational ability of specific crystals, and the possibility of evaluating the structural perfection of the studied crystals.

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca3TaGa3Si2O14 crystal samples of Z and X-cuts has been studied. Spectral dependences of transmission coefficients were measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed, in the visible region – two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm was observed on the X-cut samples. When the sample was rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands was observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect – an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum, and increases during annealing in air.

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca3TaGa3Si2O14 crystal samples of Z- and X-cuts is studied. The spectral dependences of the transmission coefficients are measured in the wavelength range (240-700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at lambda = 360 nm in the ultraviolet range is observed; in the visible region, there are two absorption bands at lambda = 460 nm and lambda = 605 nm. Additionally, a band at lambda = 290 nm is observed on the X-cut samples. When the sample is rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands is observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at lambda = 605 nm. Annealing in air leads to the opposite effect, i.e., an increase in the intensity of the absorption bands, except for the band lambda = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum and increases during annealing in air.

The effect of proton irradiation with a dose of 50 Mrad (Si) on the optical properties and defect formation in crystals of gadolinium-aluminum-gallium garnet is studied during the substitution of aluminum and gallium in the cation sublattice: Gd3Al2Ga3O12 (Al : Ga = 2 : 3) and Gd3Al3Ga2O12 (Al : Ga = 3 : 2). After irradiation with protons, the crystals change color: an additional absorption band appears in the spectrum of each crystal in the wavelength range of 400-500 nm. This is due to the formation of induced structural defects in the form of color centers. The refractive indices n(lambda) are determined by the Brewster spectrophotometric method and barely change for Al : Ga = 2 : 3 crystals, but largely increase for Al : Ga = 3 : 2. In the spectral dependences, there is a noticeable increase in the attenuation of light, which also indicates the formation of additional structural defects.

The spectra of transmisson coefficients and absorption indices of single-domain and multidomain LaBGeO5 samples have been measured. It is shown that, to measure more exactly the optical rotation ρ, it is necessary to use the spectra of transmission coefficients not only for the cases of parallel and crossed polarizers but also at other angles between them. The obtained ρ values for both samples are described quite well by only dispersion using the Drude formula. This is in agreement with the fact that the ρ value should not change during transition to the single-domain state of the crystal at a given symmetry (P31 in the ferroelectric phase and P3121 in the paraelectric phase). It is shown that the Cherenkov-type second harmonic generation (SHG) is observed only in a polydomain sample, while the second-harmonic radiation is not polarized. The domain structure of the samples was observed by scanning electron microscopy and piezoelectric force microscopy. The presence of a labyrinth-like domain structure was shown for the multidomain sample, whereas for a single-domain sample no changes in contrast were observed within the scanned region.

The influence of proton irradiation with a dose of 50 Mrad (Si) on the optical properties and defect formation in crystals of the gadolinium-aluminum-gallium garnet with the substitution of aluminumand gallium in the cationic sublattice: Gd3Al2Ga3O12 (Al: Ga = 2:3) and Gd3Al3Ga2O12 (Al: Ga = 3:2) was studied. After proton irradiation, color of crystals changes: an additional absorption band appears in the transmittance of each crystal in the wavelength range 400–500 nm. This occures due to the formation of induced structural defects as color centers. The refractive indices n(λ) were determined by the Brewster spectrophotometric method and practically did not change for Al:Ga = 2:3 crystals, but significantly increased for Al:Ga = 3:2. There is a noticeable increase in the attenuation of the light in spectral dependences, which also indicates the formation of additional structural defects.

The experience in developing and applying methods for measuring the refractive coefficients of high and middle category crystals based on multi-angle spectrophotometric reflectance methods (using the reflection spectrum from one face at a close-to-normal angle of incidence of light and the reflectance method where light falls at the Brewster angle) is peresented. Advantages and limitations of the methods and requirement to samples are described. It is shown that the reflectance method at a close-to-normal angle of incidence is applicable to optically isotropic media. The Brewster angle method is applicable to high and middle category crystals. The measurement accuracy is determined for both methods. Their applicability is verified for high- (Gd3Al2Ga3O12 : Ce) and middle category (La3Ga5.5Ta0.5O14) crystals.

Gadolinium‒aluminum‒gallium garnet crystals are grown with charge compositions Gd3AlxGa5 – xO12 (x = 1–3) and Gd3Al2Ga3O12:Ce3+. The effect high-temperature annealing in air has on the optical properties of these crystals is established. It is shown that annealing does not affect the state of cerium oxidation. X-ray fluorescence reveals a deficiency of gallium in all the investigated crystals.

The spectral dependences of transmission and absorption in the wavelength range of 200–2500 nm were measured for Ca3TaGa3Si2O14 crystals cut perpendicular to the optical axis in the initial state (without annealing) and after isothermal annealing in vacuum and in air. It was found that annealings in vacuum and air lead, respectively, to decrease and increase in the absorption band intensity. A spectrophotometric method for measuring and calculating the specific rotation angle ρ of the plane of polarization of light in gyrotropic crystals from the transmission coefficient spectra at different angles between the polarizer and analyzer is considered. The transmission spectra were normalized to eliminate the spectral shifts associated with measurement features. Spectral dependences of ρ, approximated by the extended Drude formula, were obtained for all three samples; the influence of the annealing atmosphere on the coefficients of this formula is established.

The structure and optical properties of crystals from the langasite family (La1 - xNdх)3Ga5SiO14 with different Nd content were investigated. The rotation of the light polarization plane, ρ, was calculated for these crystals from measured transmission spectra in polarized light. It is shown that for small values of ρ (~3-5 degrees/mm), it is necessary to use transmission spectra not with parallel and crossed polarizers, as is usually done, but at different angles between them, for example ±45°, to obtain better results. Circular dichroism measurements of these crystals were performed. Using Kramers-Kronig relations, the connection between the circular dichroism bands and the rotation of the light polarization plane in the absorption band region was determined. Dispersion curves of ρ values were calculated, taking into account absorption in the wavelength range of 400–1000 nm for crystals (La0.6Nd0.4)3Ga5SiO14, (La0.4Nd0.6)3Ga5SiO14, Nd3Ga5SiO14, and compared with the dispersion of ρ for langasite crystal La3Ga5SiO14. Average refractive indices and optical activity parameters of these crystals were calculated from structural data. It is shown that the dependence of the average refractive indices and ρ values on the parameters of the elementary cell, calculated under the assumption of no absorption, is linear. However, such a linear dependence is not observed for experimental ρ values, which is associated with the influence of absorption and the peculiarities of the structure (nonlinear change in the geometry of optically active regions of electron density upon replacing part of La with Nd).

В работе исследованы фотоэлектрохимические и фотокаталитические свойства пористых материалов на основе полых микросфер α-Fe 2 O 3 , характеризующихся наличием оборванных магнитных связей Fe–O–Fe, обусловленных повышенной концентрацией вакансий на границе стенка/закрытая пора. С использованием данного порошка шликерно-обжиговым методом при температуре изотермической выдержки 400°C были получены две серии пленочных образцов, нанесенных на стекло с токопроводящим слоем из суспензий двух составов: водный раствор Fe(NO 3 ) 3 + полые микросферы α-Fe 2 O 3 (серия 1 ) и водный раствор Fe(NO 3 ) 3 + полиэтиленгликоль + полые микросферы α‑Fe 2 O 3 (серия 2 ). Установлено, что пленки серии 2 имеют структуру с пространственно разделенными частицами различной дисперсности: наночастицы α-Fe 2 O 3 /полые микросферы α-Fe 2 O 3 , а пленки серии 1 преимущественно состоят из полых микросфер, объединенных "шейками", формирующимися в процессе термической обработки. Толщина пленок серии 2 составляла порядка 2 мкм, а серии 1 – 4 мкм. Структурные различия пленок двух серий оказывают существенное влияние на оптические свойства материала. Пленка серии 2 (3.50 × 10 5 м –1 ) имеет примерно в 2 раза больший коэффициент поглощения света в диапазоне длин волн 350–1500 нм в сравнении с пленкой серии 1 (1.75 × 10 5 м –1 ). Исследование фотоэлектрохимических свойств в водном растворе 0.1 M KOH показало, что потенциал начала анодной реакции для пленки серии 2 составил 0.87 В vs. Ag/AgCl, а для серии 1 – 0.97 В vs. Ag/AgCl. Для обеих пленок наблюдалось нетипичное увеличение плотности тока при длительном освещении светом при потенциале 1 В vs. Ag/AgCl, вызванное формированием на поверхности фотоанода Fe(IV). Фотокаталитические свойства материалов оценивались по скорости деградации метиленового синего. Константы скорости реакции ( k ) составили 0.015 и 0.018 мин –1 для пленок серий 1 и 2 соответственно против k для реакции без фотокатализатора 2.8 × 10 –4 мин –1 .

Представлены результаты комплексных исследований процессов дефектообразования и его влияния на оптические свойства кристаллов гадолиний-алюминий-галлиевых гранатов с частичным замещением галлия на алюминий в катионной подрешетке: Gd 3 AlGa 4 O 12 (Al : Ga = 1 : 4), Gd 3 Al 2 Ga 3 O 12 (Al : Ga = 2 : 3) и Gd 3 Al 3 Ga 2 O 12 (Al : Ga = 3 : 2), а также кристаллов Gd 3 Al 2 Ga 3 O 12 :Сe 3+ (Al : Ga = 2 : 3, легированных церием). Результаты, полученные методами рентгеновской фотоэлектронной спектроскопии и рентгенофлуоресцентного анализа, свидетельствуют о дефиците галлия по отношению к стехиометрическому составу во всех исследованных кристаллах. На основе результатов исследований рассматриваются процессы возникновения ростовых структурных точечных дефектов в кристаллах гадолиний-алюминий-галлиевого граната. Преобладающими точечными дефектами являются F -центры, также показано образование дефектов типа Шоттки и V -центров. Показано, что при легировании гранатов ионами церия также возможно образование дополнительных F ‑центров за счет введения церия. Установлено изменение коэффициентов преломления и показателей ослабления в зависимости от соотношения Al : Ga и легирования церием.

The growth system has been upgraded, technological growth parameters have been optimized, and a high-quality crystal has been grown from the LiNb 0.95 Ta 0.05 O 3 charge. Spectral dependences of the transmittance of a sample cut from this crystal have been measured before and after the transition to the single-domain state in the range of 300–700 nm with allowance for anisotropy and dichroism. Spectral dependences of the absorption coefficient α(λ) and degree of dichroism Δ(λ) have been obtained. The dependences α(λ) contain an absorption band at λ ~ 480 nm, regardless of the light propagation direction. When light propagates perpendicular to the optical axis, absorption bands at λ ~ 560, 608, 620, and 656 nm can additionally be observed. The transition to the single-domain state leads to sample bleaching. The dependences Δ(λ) for the X and Y cuts are characterized by identical extrema, whose positions correspond to the absorption bands in the dependences α(λ); additional extrema manifest themselves at λ ~ 400 and 445 nm. When light propagates along the optical axis, the dependences Δ(λ) are nonzero; they are characterized by much smaller values (in comparison with the directions perpendicular to the optical axis) and have extrema at λ ~ 440, 560, 600, 620, and 640 nm.

Optical properties of lanthanum-gallium silicate (La3Ga5SiO14), lanthanum-gallium tantalate (La3Ga5.5Ta0.5O14), calcium-tantalum-gallium silicate (Ca3TaGa3Si2O14) crystals in the near ultraviolet (UV) and visible wavelength ranges (200-800 nm) have been studied. For the first time the angles of deviation of the moments of the dipole transition spectral dependences theta(λ) were used to characterize the absorption processes in these crystals. These dependences make it possible to reveal absorption bands that are weakly noticeable on the transmission coefficients spectral dependences, and to estimate the degree of deviation of the dispersion dependence theta(λ) from the value theta=45o corresponding to an ideal ordered crystal. Analysis of theta(λ) dependencies showed that in the studied wavelength range, the lowest deviation from theta =45o is observed in Ca3TaGa3Si2O14, and the highest - in La3Ga5SiO14. The coefficients of the specific rotation angle of the polarization plane rho were obtained by the spectrophotometric interference method in polarized light. The measured values are best approximated by the Vyshin equation. For the first time, dependences of the modified Drude formula 1/rho=f(λ2) were calculated for these crystals. These dependences should be linear in case of an ideal crystal. The largest deviation from the linear dependence is observed for La3Ga5SiO14 crystals, and the lowest for Ca3TaGa3Si2O14. The discrete values of the refractive coefficients No and Ne were measured by the prism method. La3Ga5.5Ta0.5O14 crystals have the highest refractive coefficients, Ca3TaGa3Si2O14 crystals have the lowest. The obtained values are approximated by the Sellmeier equation.

— We have studied photoelectrochemical and photocatalytic properties of porous materials based on hollow α-Fe 2 O 3 microspheres, characterized by the presence of dangling magnetic Fe–O–Fe bonds due to an increased oxygen vacancy concentration on the wall/closed pore interface. Using such powder and firing slips at an isothermal holding temperature of 400°C, we obtained two series of thin-film samples on glass with a conductive layer from suspensions of two compositions: aqueous Fe(NO 3 ) 3 solution + hollow α-Fe 2 O 3 microspheres (series 1 ) and aqueous Fe(NO 3 ) 3 solution + polyethylene glycol + hollow α-Fe 2 O 3 microspheres (series 2 ). The films of series 2 were shown to have a structure with spatially separated particles differing in size: α-Fe 2 O 3 nanoparticles and hollow α-Fe 2 O 3 microspheres. The films of series 1 consisted predominantly of hollow microspheres connected by “necks” formed during heat treatment. The thickness of the films of series 2 was of order 2 μm and that of the films of series 1 was of order 4 μm. The structural distinctions between the films of the two series had a significant effect on the optical properties of the material. In the wavelength range 350–1500 nm, the absorption coefficient of the films of series 2 (3.50 × 10 5 m –1 ) was about twice that of the films of series 1 (1.75 × 10 5 m –1 ). Photoelectrochemical characterization in an aqueous 0.1 M KOH solution showed that the onset potential for the anodic reaction was 0.87 V vs. Ag/AgCl in the case of the films of series 2 and 0.97 V vs. Ag/AgCl in the case of series 1 . The films of both series showed an unusual increase in current density during prolonged illumination at a potential of 1 V vs. Ag/AgCl, due to Fe(IV) formation on the photoanode surface. Photocatalytic properties of the materials were assessed from the rate of methylene blue degradation. The reaction rate constant ( k ) was determined to be 0.015 and 0.018 min –1 for the films of series 1 and 2 , respectively, whereas the k of the photocatalyst-free reaction was 2.8 × 10 –4 min –1 .

Nominally pure lanthanum-gallium tantalate La3Ga5.5Ta0.5O14 crystals doped with aluminum, silicon and gallium oxide to above stoichiometric content have been grown by the Czochralski technique in iridium crucibles in argon and in agron with addition of oxygen atmospheres. The transmittance spectra of the crystals have been measured on a Cary-5000 UV-Vis-NIR spectrophotometer in the 200–800 nm range. Absorption spectra α(λ) have been plotted on the basis of the experimental data. The absorption spectra of the undoped crystals grown in an oxygen-free atmosphere have one weak absorption band at λ ~ 290 nm. The absorption spectra of the crystals grown in an agron with addition of oxygen have absorption bands at λ ~ 290, 360 and 480 nm. We show that for the crystals grown in an oxygen-free atmosphere, gallium doping to above stoichiometric content reduces the intensity of its only λ ~ 290 nm absorption band. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-free atmosphere significantly reduces the intensity of the λ ~ 290 nm absorption band and increases the intensity of the λ ~ 360 and 480 nm bands. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-containing atmosphere reduces the intensity of the λ ~ 360 and 480 nm bands and increases the intensity of the λ ~ 290 nm absorption band. Silicon doping of these crystals significantly reduces the intensity of the λ ~ 480 nm band and also reduces the intensity of the λ ~ 290 and 360 nm bands.

Coatings in the Ta-Si-N system were deposited by magnetron sputtering in the Ar, N-2 atmosphere and Ar+N-2 gas mixtures. Coatings have been studied in terms of structure and composition, optical characteristics, adhesion strength, fracture toughness, mechanical and tribological properties, as well as oxidation resistance. Nitrogen added to the coatings inhibits the columnar grain growth of the h-TaSi2 phase due to formation of amorphous nitrogen-containing interlayers. The coating deposited in an atmosphere of nitrogen was characterized by optical transmittance up to 90% and reflectivity up to 32% in the visible and infrared spectra. Extremal dependence of adhesion strength, fracture toughness and hardness on nitrogen concentration was observed, with the maximum (Lc(2) >31 N, L=20 N and H=26.7 GPa) corresponding to the Ar:N-2 gas ratio = 1:2. The coating fabricated in an atmosphere of Ar had the lowest friction coefficient (similar to 0.6) and wear rate (< 0.2 x 10(-4) mm(3)N(-1)m(-1)). The coatings with high nitrogen content were resistant to oxidation at temperatures up to 1200 degrees C because of the higher volume fraction of the amorphous phase with the composition close to Si3N4.

Single crystal calcium molybdate CaMoO 4 is a well-known material. However the interest to CaMoO 4 has recently grown due to a number of its important applications including as a working material in cryogenic scintillation bolometers. CaMoO 4 single crystals acquire blue color during growth due to the presence of color-center type defect centers which are unacceptable for optical applications. Color can be eliminated through annealing in an oxygen containing atmosphere, following which required optical components can be produced from the single crystals by mechanical treatment (cutting, polishing etc.). Therefore assessment of the mechanical properties of these single crystal materials is an important task for the optimal solution of issues occurring in the fabrication of optical components and their further practical application. There are but scarce data on the mechanical properties of CaMoO 4 , and the available ones have been reported without allowance for anisotropy. There is a significant scatter of data on the Mohs hardness of the single crystals, ranging from 3.3 to 6 in different publications. In this work we present data on calcium molybdate single crystals in the initial state and after high-temperature anneals of different durations in an oxygen containing atmosphere. We show that long-term annealing leads to decolorization of the crystals. Calcium molybdate single crystals prove to be quite brittle: the brittleness index Zp of the crystals in the initial state is the highest and equals 5, while annealing reduces the brittleness index to 4. The Palmqvist toughness factors S have been calculated The limit indentation destruction loads F lim have been determined and annealing in an oxygen containing atmosphere has been shown to increase F lim by 2.5 times for the Z cut and by 10 times for the X cut. The microhardness of the crystals has been shown to exhibit a II type anisotropy: the microhardness of all the specimens was higher for the Z cut than for the X cut. The microhardness anisotropy coefficients KH of the specimens have been evaluated. The bond ionicity degree I has been calculated on the basis of the experimentally measured microhardness.