Two-phase Ceramics Research Articles

Optical properties of crystals and two-phase ceramics of the AgCl0.25Br0.75 – AgI system

Research of materials’ optical properties is critical for further development and manufacturing of optical products. While recently, single crystals and two-phase ceramics of the AgCl0.25Br0.75 – AgI system have been developed by the authors. This work is focused on studying the transmission ranges, refractive index dispersion, optical losses, and photoresistance of materials in the AgCl0.25Br0.75 – AgI system, as well as comparing the properties of single-crystals and ceramics. The materials are transparent in the visible and IR regions from 0.49 to 54 um, as well as in the terahertz (far IR and millimeter regions) of 300–1500 um (0.3–1.0 THz). For all compositions, the refractive index in the IR varied from 2.107 to 2.436. The materials’ absorption coefficients were (0.06–6.67) ∙ 10-4 in the middle IR, which is lower compared to other halide materials known and indicates low optical loss. Finally, both single-crystals and two-phase ceramics showed a trend towards an increase in photoresistance with a rise of the AgI content in the AgCl0.25Br0.75 solid solution. After UV irradiation, the materials showed a decrease in transmission in the visible and middle IR (to 10 µm) with negligible loss at a wavelength of 10 µm or more. For a single crystal and two samples of ceramics with a composition of 20 mol. % AgI in AgCl0.25Br0.75, a comparison of properties was conducted in this study. Based on the comparison results, close but not identical values of the refractive indices, an increase in the absorption coefficient for ceramic materials, and a low photoresistance of the sample obtained from the mechanical mixture were revealed. The last two characteristics are associated with the high heterogeneity of two-phase ceramics based on a mechanical mixture, which leads to a deterioration in functional properties. These results prove high prospects for the use of these materials in fiber optics and photonics for medical technologies, thermography, and optoelectronics.

The connection between the accumulation of structural defects caused by proton irradiation and the destruction of the near-surface layer of Li4SiO4 – Li2TiO3 ceramics

The key problem of using lithium-containing ceramics as materials of breeders for the propagation of tritium in thermonuclear reactors is phase stability, as well as the preservation of strength and thermophysical parameters of ceramics during their operation, which is accompanied by the accumulation of fission products in the near-surface layers, alongside mechanical influences from the outside. Moreover, in contrast to other types of ceramics, the presence of lithium in the composition of the samples under study leads to limitations in the use of classical analysis methods (scanning electron microscopy, energy dispersive analysis or optical spectroscopy) of structural changes caused by the accumulation of radiation damage, which requires the use of more complex methods for the assessment of the defect concentration in the structure, as well as establishing their relationship with the deterioration of strength and thermophysical parameters, playing a key role in determining the stability mechanisms and further exploitation of ceramics for tritium production. In this regard, the aim of the study is to determine the kinetics of changes in the near-surface layer of two-phase Li4SiO4 – Li2TiO3 ceramics associated with the accumulation of structural distortions caused by irradiation, as well as their relationship with strain embrittlement and disorder. During the studies, it was found that the accumulation of implanted hydrogen in the near-surface layer under high-dose irradiation initiates deformation distortion processes, the intensity of which depends on the ratio of components in the ceramics, according to which the optimal compositions of two-phase ceramics are ratios of components from 0.3 to 0.6. Determination of the type of defects in the composition of the damaged layer, as well as their concentration, was carried out using the electron spin resonance (ESP) method. During the studies, it was found that at low irradiation fluences, the dominant role in the accumulation of structural defects is played by vacancy defects associated with E′-centers, the formation of which is associated with structural distortions, while as the fluence grows, the structure is dominated by deformation disordering caused by the accumulation of Ti3+ defects and HC2 centers (SiO43-), the concentrations of which have a clear dependence on the phase composition of the ceramics.

Effect of low-energy ion modification of microcomposite (1-x)WO3 – xZnO ceramics on improved photocatalytic decomposition efficiency

The main purpose of this work is to study the possibility of using ionic modification of (1-x)WO3 – xZnO microcomposite ceramics in order to elevate their photocatalytic activity, as well as enhance stability to degradation during long-term use and exposure to aggressive environments. The objects of study were (1-x)WO3 – xZnO ceramics obtained by solid-phase synthesis from tungsten and zinc oxides. Moreover, according to X-ray phase analysis data, it was found that variations in the ratio of oxide components during their mechanical activation and subsequent thermal annealing result in the formation of two-phase ceramics with different contents of the zinc tungstate phase. The results of experiments on the photocatalytic decomposition of the organic dye Rhodamine B revealed that two-phase WO3/ZnWO4 ceramics have the greatest efficiency, for which ion irradiation with fluences of 1015 ––5 × 1015 leads to a growth in the decomposition efficiency from 80 to 95 %. At the same time, the dominant effect influencing the photocatalytic decomposition efficiency growth is the change in the band gap of the ceramics, associated with the accumulation of the athermal effect of energy dissipation of incident ions on the change in electron density. The results of assessment of changes in the strength and structural parameters of (1-x)WO3 – xZnO ceramics depending on the time spent in model solutions (to simulate the effects of environments with different acidity levels) indicate a positive effect of ionic modification on enhancing stability to degradation and softening as a result of the accumulation of amorphous inclusions.

STUDY OF THE EFFECT OF THE FORMATION OF TWO-PHASE CERAMICS BASED ON NEODYMIUM ZIRCONATE DUE TO DOPING WITH MGO AND Y2O5 ON THE STABILITY OF STRENGTH AND THERMOPHYSICAL PARAMETERS UNDER IRRADIATION

The work presents the study results of the determination of the resistance of neodymium zirconate doped with MgO and Y2O5 to radiation damage stemming from irradiation with heavy ions akin to nuclear fuel fission fragments. The attraction towards this type of ceramics stems from its potential to raise the operational temperatures within the core of next-generation nuclear reactors. This is owed to its superior thermal conductivity when compared to zirconium dioxide, coupled with the heightened strength parameters that signify the ceramics' resistance against external factors. The main results of this study are to determine the influence of the formation of substitution or interstitial phases when adding magnesium and yttrium oxides to the composition, on increasing the stability of the strength and thermophysical parameters of neodymium zirconate to the radiation defects accumulation in the damaged surface layer. During the studies, it was found that the formation of impurity phases in the form of MgO inclusions (when it is added to the composition) and a substitution phase of the Y2Zr2O7 type (with the addition of Y2O5) results in an elevation in the hardness and crack resistance stability of neodymium zirconate ceramics, which indicates the positive effect of doping linked to the formation of additional interphase boundaries that prevent strain embrittlement of the damaged layer under high-dose irradiation. During determination of the thermophysical parameters of the studied neodymium zirconate ceramics, it was observed that the formation of interphase boundaries during doping not only enhances thermal conductivity but also mitigates the decline in the thermal conductivity coefficient during irradiation for two-phase ceramics in comparison with undoped neodymium zirconate ceramics.

Optical properties of crystalline materials based on AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems

For the development of optical technologies aimed at research, diagnostics and operation in a wide spectral range, the creation of new materials capable of being highly transparent and effective for transmitting electromagnetic waves in the visible, IR and THz regions is required. This article studies the properties of single crystals and two-phase ceramics based on solid solutions of the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems. The materials showed transparency in the range of 0.4–60.0 and 350–1500 μm (0.20–0.86 THz). With an increase in the proportion of thallium halides in the AgCl0.25Br0.75 solid solutions, a shift and the transmission spectrum broadening to longer wavelengths was observed. These effects are typical for compounds with both Fm3m and Pm3 m type cubic crystal lattice. The refractive indices of the developed materials have normal wavelength dispersion and vary from 2.107 to 2.539 depending on the system and composition. The indicators for solid solutions with an intermediate composition of homogeneity regions lie within the values characteristic of boundary compositions. Based on this data a description of the index dependence by the Sellmeier equation, adapted by Fleming, was obtained. The refractive indices imaginary parts of all developed materials were 0.11*10−4–3.55*10−4, which was 2–4 times lower in comparison with other substances based on silver and thallium halides. The materials were characterized by a photostability improvement with an increase in the part of thallium halides in the solid solution, as well as with a growth in the amount of the orthorhombic phase in the case of two-phase ceramics. The materials showed low values of optical losses, as well as high functional properties. This makes single crystals and ceramics promising for transmission and fiber optics designed to operate in a wide spectral range.

Studies of irradiated two-phase lithium ceramics Li4SiO4/Li2TiO3 by thermal desorption spectroscopy

Two-phase ceramics Li2TiO3-Li4SiO4 are one of the potentially promising materials for creating a ceramic blanket for DEMO reactor. However, until now, a limited number of studies have been carried out on the release of tritium from this material under the influence of neutron irradiation, which poses fundamental problems for its application.In this work, the pebbles of two-phase lithium ceramics consisting of 25 mol% Li2TiO3 and 75 mol% Li4SiO4 were studied using thermal desorption spectroscopy (TDS) after their irradiation with neutrons at the WWR-K research reactor. Under the conditions of the irradiation experiment, which lasted 21.5 days at a reactor power of 6 MW, the samples were exposed to thermal neutrons with a flux density of 2·1013n/(cm2 × s). The thermal neutron fluence accumulated as a result of irradiation was 3.7·1019 cm−2.It has been established that tritium comes out mainly in the form of HT molecules and has three visible TDS peaks, which can be described by three rates of the first-order desorption reaction with an activation energy of 90 kJ/mol. Experiments have shown that the main amount of tritium is evenly distributed throughout the pebble’s pores and voids. Its yield is determined by desorption and transfer from inner voids to the boundaries that communicate with the outer surface of the sample. The kinetics of tritium release depends on the number, size and depth of the exit paths of such areas inside the ceramic.

Effects of Composition Variations on Mechanochemically Synthesized Lithium Metazirconate-Based Ceramics and Their Resistance to External Influences

The study examines the influence of variations in the compositions of components for the production of lithium-containing ceramics based on lithium metazirconate obtained by the method of mechanochemical grinding and subsequent thermal sintering. For component variation, two compositions were used, consisting of zirconium dioxide (ZrO2) and two distinct types of lithium-containing materials: lithium perchlorate (LiClO4·3H2O) and lithium carbonate (Li2CO3). Adjusting the concentration of these components allowed for the production of two-phase ceramics with varying levels of impurity phases. Using X-ray phase analysis methods, it was determined that the use of LiClO4·3H2O results in the formation of a monoclinic phase, Li2ZrO3, with impurity inclusions in the orthorhombic phase, LiO2. On the other hand, when Li2CO3 is used, the resulting ceramics comprise a mixture of two phases, Li2ZrO3 and Li6Zr2O7. During the studies, it was established that the formation of impurity inclusions in the composition of ceramics leads to an increase in the stability of strength properties with varying mechanical test conditions, as well as stabilization of thermophysical parameters and a decrease in thermal expansion during long-term high-temperature tests. It has been established that in the case of two-phase ceramics Li2ZrO3/Li6Zr2O7 in which the dominance of the Li6Zr2O7 phase is observed during high-temperature mechanical tests, a more pronounced decrease in resistance to cracking is observed, due to thermal expansion of the crystal lattice.

Study of the Effect of Adding Nb2O5 on Calcium Titanate-Based Ferroelectric Ceramics

This paper considers the effect of adding niobium oxide (Nb2O5) to ferroelectric ceramics based on calcium titanate (CaTiO3), and establishes a connection between the observed alterations in strength and dielectric properties and the variation in the Nb2O5 dopant concentration in the ceramics’ composition. The method of mechanochemical solid-phase synthesis was used as the main method for obtaining the ceramics, followed by thermal sintering under specified conditions in order to form a stable phase composition of the ceramics, and to initialize phase transformations in the composition. Based on the assessment of the phase composition of the resulting ceramics, it was determined that a growth in the Nb2O5 dopant concentration beyond 0.10 mol results in the formation of an orthorhombic-phase CaNb2O4 of the Pbcm(57) spatial system, the weight contribution of which grows. A growth in the Nb2O5 additive concentration results in the formation of two-phase ceramics, the formation of which allows for an enhancement in the mechanical strength of ceramics and resistance to external influences. During the study of the dependence of the strength properties on the dopant concentration alteration, a three-stage change in hardness and crack resistance was established, regarding both structural ordering and phase transformations. The measurement of dielectric characteristics showed the direct dependence of dielectric losses and the dielectric constant on the phase composition of ceramics.

Study of Gas Swelling Processes under Irradiation with Protons and He2+ Ions in Li4SiO4–Li2TiO3 Ceramics

One of the important areas of research in the energy sector is the study of the prospects for using new types of nuclear fuel, including tritium, which is one of the most promising types of fuel for thermonuclear energy. At the same time, for the production of tritium in the required quantities, the one that is the most optimal is the use of blanket materials based on lithium-containing ceramics. This is where tritium is released from lithium under the influence of neutron irradiation. The paper presents the results of an investigation of the influence of two-phase ceramics based on Li4SiO4–Li2TiO3 compounds on the resistance to external influences (mechanical loads) during the accumulation of hydrogen and helium (He2+) in the near-surface layer. The interest in such studies is primarily related to the search for solutions in the field of creating high-strength materials for tritium generation for its further use as nuclear fuel for thermonuclear fusion, as well as to the study of the mechanisms of the influence of different phases on the changes in the strength properties of ceramics, which provides an opportunity to expand fundamental knowledge in this area. The proposed method of obtaining two-phase ceramics by mechanical-chemical mixing and subsequent sintering into spherical particles enables the production of well-structured, high-strength ceramics of specified geometric dimensions (limited only by the dimensions of the mold) with a controlled phase ratio. During the experiments, it was found that increasing the content of Li4SiO4 phase in ceramics leads to an increase in strength characteristics (hardness, resistance to cracking) by 15–20% compared to single-phase ceramics. The most optimal composition of two-phase ceramics with high resistance to destructive embrittlement is the ratio of phases 0.75Li4SiO4–0.25Li2TiO3. One of the factors explaining the increase in resistance to destructive embrittlement under high-dose irradiation for two-phase ceramics is the increased dislocation density and the presence of interphase or intergranular boundaries, the high concentration of which leads to the creation of additional obstacles to the agglomeration of hydrogen and helium in the near-surface layer.

The Effect of the Addition of Aluminum Nitride to the Composition of NiAl2O4 Ceramics on Hydrogenation Processes and the Increase in Resistance to Swelling and Degradation

This work examines the effects of the formation of impurity inclusions in the structure of NiAl2O4 ceramics when aluminum nitride is added to them and the occurrence of a reinforcement effect that prevents hydrogenation processes and the subsequent destruction of conductive and thermophysical characteristics. The appeal of ceramics possessing a spinel crystal structure lies in their potential use as ceramic fuel cells for both hydrogen generation and storage. Simultaneously, addressing the challenges related to ceramic degradation during hydrogenation, a critical aspect of hydrogen production, can enhance the efficiency of these ceramics while lowering electricity production costs. The selection of aluminum nitride as an additive for ceramic modification is based on its remarkable resistance to structural damage accumulation, its potential to enhance resistance to high-temperature degradation, and its ability to bolster strength properties. Moreover, an examination of the alterations in the strength characteristics of the examined samples subjected to hydrogenation reveals that the stability of two-phase ceramics is enhanced by more than three to five times compared to the initial ceramics (those without the addition of AlN). Additionally, it was noted that the most significant alterations in both structure and strength become apparent at irradiation fluences exceeding 1014 proton/cm2, where atomic displacements in the damaged ceramic layer reach over 5 dpa. During the evaluation of thermophysical properties, it was discerned that ceramics featuring an impurity phase in their composition exhibit the highest stability. These ceramics demonstrated a reduction in the thermal conductivity coefficient of less than 1% at the peak irradiation fluence.

STUDY OF THE INFLUENCE OF MgO DOPING ON THE THERMOPHYSICAL PROPERTIES OF CERAMICS BASED ON LITHIUM METAZIRCONATE

The paper presents the results of studying the effect of doping with magnesium oxide (MgO) of lithium-containing ceramics based on lithium metazirconate (Li2ZrO3) on the change in the thermophysical parameters of ceramics. The method of mechanochemical synthesis followed by high-temperature annealing at a temperature of 1300 °C, used to initiate the processes of phase transformations from structural ordering, was chosen as the main method for obtaining ceramics, as well as for performing MgO doping processes. In the course of the studies, it was found that an increase in the concentration of the MgO dopant above 0.10 mol leads to the formation of impurity inclusions in the structure of ceramics in the form of a tetragonal phase MgLi2ZrO4, the content of which increases with an increase in the concentration of the dopant. In the case of a dopant concentration of 0.25 mol, the phase composition of ceramics is an equiprobable distribution of two phases, monoclinic Li2ZrO3 and tetragonal MgLi2ZrO4. In the course of measuring thermophysical parameters, it was found that the formation of the MgLi2ZrO4 phase in the composition of ceramics leads to an increase in the thermal conductivity by 5–10%, and in the case of an equiprobable distribution of phases in two-phase MgLi2ZrO4– Li2ZrO3 ceramics, the increase in thermal conductivity is more than 25% in comparison with undoped ceramics. An increase in the efficiency of heat-conducting properties for two-phase ceramics is due to an increase in the rate of phonon heat transfer due to additional interfacial boundaries, as well as an increase in the degree of structural ordering and density of ceramics.

Optical materials for IR fiber optics based on solid solutions of AgCl0.25Br0.75 – TlCl0.74Br0.26, AgCl0.25Br0.75 – TlBr0.46I0.54 systems

The development of optical materials, that are transparent from the visible to the far IR without absorption windows, including fiber optics materials, continues to be an urgent scientific problem, which is associated with high prospects for their application in wide-spectrum systems, IR and THz technology. This article is devoted to the development of materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems from constructing phase diagrams to synthesis of single crystals and optical ceramics and their transmission properties investigation. According to the results of studying the phase diagram of the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, homogeneity regions of 0–7 mol. % and 95–100 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75, in which there are single-phase solid solutions with the structure Fm3m and Pm3 m, respectively, were obtained. In this diagram, regions of heterogeneity with a composition of 7–79 mol. % and 79–95 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and a mixture of two phases in the first region Fm3m and R-3, and in the second region Pm3 m and R-3 were found. Within the AgCl0.25Br0.75 – TlBr0.46I0.54 system's phase diagram, homogeneity regions with compositions of 0–15 mol. % and 92–100 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and similar structures Fm3m and Pm3 m, respectively, were determined. This system also contains regions of heterogeneity with compositions of 15–36 mol. %. and 69–92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 with phase composition Fm3m and R-3, and Pm3 m and R-3. In each system, compositions were selected from the homogeneity and heterogeneity regions, and samples of single crystals and two-phase ceramics were synthesized. For the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, a single crystal with a composition of 3 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and two-phase ceramics of 7, 31, 86, 92 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 were obtained. Single crystals 3, 6, 9, 92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and ceramics 32, 76 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 were synthesized in AgCl0.25Br0.75 – TlBr0.46I0.54 system. The samples are 35 ± 5 mm high and 10 ± 0.1 mm in diameter, and their color varies from yellow to orange depending on the composition. The transmittance ranges of all synthesized samples were investigated. The study was carried out on polycrystalline plates with a diameter of 15 ± 5 mm, thickness of 400 ± 5 μm, and surface roughness Ra = 0.2 μm. The crystallite size of the alloying phase R-3 in the optical ceramics was less than 100 nm. For AgCl0.25Br0.75 – TlCl0.74Br0.26 system materials, the transmission spectra covered the region from 0.4 to 55.0 μm. Materials based on the AgCl0.25Br0.75 – TlBr0.46I0.54 system showed transmission in the wavelength range of 0.49–60.0 μm. All materials are transparent in the wide region without absorption windows with a transparency level up to 79%. Thus, new optical materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems have been developed, which have a wide transmission range from the visible to the IR. This opens broad prospects for their use as an optical material for wide-spectrum devices, as well as IR fiber optics.

Optical properties of single crystals and ceramics based on silver and thallium (I) halides in the range of 0.3–30.0 THz

This paper is devoted to single crystals and two-phase ceramics based on the TlBr0.46I0.54 – AgI, TlCl0.74Br0.26 – AgI, AgBr – AgI systems' properties study in the THz range of 0.3–30.0 THz. Plane-parallel windows were manufactured based on single crystals of composition 6, 13 mol.% AgI in TlBr0.46I0.54 and 3, 13, 25 mol.% AgI in AgBr, as well as based on two-phase ceramic composition 19, 25 mol.% AgI in TlBr0.46I0.54, 7, 14, 20, 27 mol.% AgI in TlCl0.74Br0.26 and 36 mol.% AgI in AgBr. The materials showed high transmission in the THz with an absorption band. Single crystals and ceramics of the TlBr0.46I0.54 – AgI system are transparent in the ranges 0.3–0.67 and 5–30 THz, which corresponds to wavelengths 447–1000 μm and 10–60 μm. The maximum transparency of the materials in the 5–30 THz range is 70 %, in the other ranges it reaches 40 %. Ceramics of the TlCl0.74Br0.26 – AgI system transmit THz radiation in the 0.3–0.85 and 6–30 THz (353–1000 μm and 10–50 μm) regions. The transparency reaches 60 % in the frequency range of 0.3–0.85 THz and 77 % in the range of 6–30 THz. In the case of AgBr – AgI system, the samples were transparent from 0.3 to 1 THz (300–1000 μm) with a maximum transparency of 77 % and from 5.55 to 30 THz (10–54 μm) with transparency up to 60 %. The attenuation coefficients for each system were quite low 0.03–0.8 cm−1 depending on the composition and system. The value of the coefficients decreased with decreasing emission frequency. The paper also compares the developed THz materials with known materials. A multiple characterization of each class of THz optical materials is given. As a result of the studies, it is found that the set of obtained properties makes the developed THz materials based on silver halides and monovalent thallium halides promising potential materials for application in THz devices and devices for a wide range of purposes.

Synthesis and Structural and Strength Properties of xLi2ZrO3-(1-x)MgO Ceramics-Materials for Blankets.

The article considers the effect of doping with magnesium oxide (MgO) on changes in the properties of lithium-containing ceramics based on lithium metazirconate (Li2ZrO3). There is interest in this type of ceramics on account of their prospects for application in tritium production in thermonuclear power engineering, as well as several other applications related to alternative energy sources. During the investigations undertaken, it was found that variation in the MgO dopant concentration above 0.10-0.15 mol resulted in the formation of impurity inclusions in the ceramic structure in the form of a MgLi2ZrO4 phase, the presence of which resulted in a rise in the density of the ceramics, along with elevation in resistance to external influences. Moreover, during experimental work on the study of the thermal stability of the ceramics to external influences, it was found that the formation of two-phase ceramics resulted in growth in the preservation of stable strength properties during high-temperature cyclic tests. The decrease in strength characteristics was observed to be less than 1%.

Synthesis, Structural Properties, and Resistance to High-Temperature Degradation of Perovskite Ceramics Based on Lanthanum–Strontium Ferrite

This work is dedicated to the study of the properties of perovskite ceramics based on lanthanum–strontium ferrite, and to the evaluation of their resistance to long-term thermal aging. As a method for obtaining perovskite ceramics, the method of solid-phase mechanochemical grinding and consequent thermal annealing of the resulting mixtures was chosen. The novelty of the study consists in the assessment of the phase transformation dynamics in lanthanum–strontium ferrite-based ceramics in relation to the annealing temperature, alongside the study of the effect of the phase composition of ceramics on the resistance to high-temperature aging, which is characteristic of the operating modes of these ceramics as materials for solid oxide fuel cells. To study the properties, the methods of scanning electron microscopy, energy dispersive analysis, and scanning electron microscopy were applied. Pursuant to the outcome of elemental analysis, it was established that no impurity inclusions appear in the ceramic structure during the synthesis, and a growth in the annealing temperature results into a decline in the grain size and a growth in their density. During the analysis of the acquired X-ray diffraction patterns, it was found that a growth in the annealing temperature above 500 °C results in phase transformations of the LaFeO3/SrFe2O4 → La0.3Sr0.7FeO3/LaSr2FeO8/La3FeO6 type, followed by structural ordering and a decline in deformation distortions with a growth in the annealing temperature. An analysis of the conductive properties of ceramics has established that the dominance of the La0.3Sr0.7FeO3 phase in the structure results in a growth in conductivity and a decline in resistance. Life tests for degradation resistance have shown that for three-phase ceramics, the rate of degradation and amorphization is significantly lower than for two-phase ceramics.

Magnocolumbites Mg1–xMxNb2O6−δ (x = 0, 0.1, and 0.2; M = Li and Cu) as New Oxygen Ion Conductors: Theoretical Assessment and Experiment

MgNb2O6 with a columbite structure was theoretically predicted as a prospective oxygen ion conductor. This compound was successfully synthesized by the Pechini method. The Li- and Cu-doped samples Mg1–xMxNb2O6−δ (x = 0.1 and 0.2; M = Li and Cu) were prepared in the same way. The columbite structure (Sp.gr. Pbcn) was formed for the samples with x = 0 and x(Cu) = 0.1 and 0.2, while Li-doping led to the formation of two-phase ceramics with Mg1–xLixNb2O6−δ and LiNbO3 components. The lithium and copper doping led to a decreasing sintering temperature by 100–200 °C down to ∼1050 °C. For Mg1–xLixNb2O6−δ (x = 0, 0.1, and 0.2), the experiments revealed pure oxygen ion conductivity of σ ∼10–5 Scm–1 at 800 °C, an activation energy Ea,σ of 0.86 eV, and good stability in a wide range of temperature, oxygen partial pressure, and in an atmosphere of carbon dioxide. For the Cu-doped samples, mixed n-type electronic and oxygen ion (T > 400 °C) conductivity was determined up to 2 × 10–3 Scm–1 at 800 °C with Ea,σ = 0.21 eV at x(Cu) = 0.2.

Study of Radiation-Induced Damage Processes in CeZrO4–YZrO3 Ceramics Caused by Helium Irradiation

Composite oxide ceramics CeZrO4-YZrO3 obtained by mechanochemical synthesis were chosen as objects of study. The most dangerous type of radiation defect in structural materials is associated with helium accumulation in the structure of the near-surface layer. This can lead to the destruction and swelling of the material, resulting in a decrease in its strength and thermal characteristics. During the studies, it was found that the most significant structural changes (deformation of the crystal lattice, the magnitude of microdistortions of the crystal lattice) are observed with irradiation fluence above 5×1016 ion/cm2, while the nature of the changes is exponential. X-ray diffraction analysis found that the nature of the crystal structure deformation has a pronounced type of stretching due to the accumulation of implanted helium and its subsequent agglomeration. A comparative analysis with data on microdistortions of the crystal lattice and the values of microhardness and softening of ZrO2 and CeO2 showed that two-phase ceramics of the cubic type CeZrO4-YZrO3 are more resistant to radiation-induced degradation than single-phase ZrO2 and CeO2. Results of strength and thermophysical characteristics showed that the presence of two phases increases resistance to destruction and disorder, leading to a decrease in strength and thermal conductivity.

Synthesis of optical materials based on the TlBr0.46I0.54 – AgI system and investigation of their optical properties

In order to obtain optical materials for operation in the visible, infrared and terahertz regions with high functional properties and suitable for the manufacture of optical fibers, technologies were developed and the properties of single crystals and ceramics based on the TlBr0.46I0.54 – AgI system were studied. According to the phase diagram of the system TlBr0.46I0.54 – AgI, it is possible to synthesize single crystals with a content of up to 18 mol. % AgI in TlBr0.46I0.54, as well as two-phase ceramics with a content from 18 to 43 mol. % AgI in TlBr0.46I0.54. Two compositions of each of the material types were synthesized by the directed crystallization method: single crystals of 6 and 13 mol. % composition AgI in TlBr0.46I0.54 and optical ceramics of compositions 19 and 25 mol. % AgI in TlBr0.46I0.54. It was possible to achieve an increase in the transmission range from 0.495 to 55.0 µm and to 0.504–60.0 µm with a lower refractive index: from 2.203 to 2.363 in the wavelength range of 0.5–14.0 µm, depending on the composition, by introducing AgI into the solid solution TlBr0.46I0.54. The developed materials showed resistance to ultraviolet, as well as radiation resistance under β-irradiation with doses up to 1000 kGy.

STUDY OF THE MICROSTRUCTURE AND PHASE FORMATION IN CERAMICS BASED ON Zn, Sn AND Ti OXIDES

Ceramics was obtained from the mixture of ZnO, SnO2 and TiO2 nanopowders by the method of solid-state sintering at 1123 K and 1443 K. The indicated nanopowders are used as components in arc dampers and for dispersion-strengthening in silver-based electrical contact materials. The phase formation and microstructure of the obtained material were studied by the methods of scanning electron microscopy, energy dispersive microanalysis and X-ray phase analysis. It is shown that at a sintering temperature of 1123 K a dispersed structure was formed, with the size of the Zn2TiO4 and ZnO phases being 0.5 – 1.0 µm. The solid phase reactions in the system ZnO/TiO2 at Тsint = 1123 K resulted in the formation of two-phase ceramics ZnO/Zn2TiO4 with the residual amounts of the phases of zinc and tin oxides. At Тsint = 1443 K there occurred the grain growth, Zn2SnO4 became the predominant phase and there remained a certain amount of the zinc and tin oxide phases.

Study of the Effect of Two Phases in Li4SiO4-Li2SiO3 Ceramics on the Strength and Thermophysical Parameters.

The paper studies the effect of Li2SiO3/Li4SiO4 phase formation in lithium-containing ceramics on the strength and thermophysical characteristics of lithium-containing ceramics, which have great prospects for use as blanket materials for tritium propagation. During the phase composition analysis of the studied ceramics using the X-ray diffraction method, it was found that an increase in the lithium component during synthesis leads to the formation of an additional orthorhombic Li2SiO3 phase, and the main phase in ceramics is the monoclinic Li4SiO4 phase. An analysis of the morphological features of the synthesized ceramics showed that an increase in the Li2SiO3 impurity phase leads to ceramic densification and the formation of impurity grains near grain boundaries and joints. During determination of the strength characteristics of the studied ceramics, a positive effect of an increase in the Li2SiO3 impurity phase and dimensional factors on the strengthening and increase in the resistance to external influences during compression of ceramics was established. During tests for resistance to long-term thermal heating, it was found that for two-phase ceramics, the decrease in strength and thermophysical characteristics after 500 h of annealing was less than 5%, which indicates a high resistance and stability of these ceramics in comparison with single-phase orthosilicate ceramics.