This article inform about creating a new variant of humidity to electricity converter (HEC) based on different types of zirconia powders-double-layer HEC. The powders that were used in the work differ in chemical composition (Y-and Mg-stabilized ZrO2) and surface properties (positive and negative charged) and allow realizing the charge separation of moving water ions and generate the electric power under ion gradient diffusion in the presence of water molecules in the atmosphere without humidity gradient. Due to the opposite ionic conductivity with respect to protons and OH groups, this HEC separate charges more efficiently compared with converters operating only by the streaming potential mechanism under humidity gradient conditions. The resulting humidity to electricity converter can generate, for a long time, an open-circuit voltage of up to 120 mV combined with a power density of 2.2 mu W on the optimal load resistance. Reducing the internal resistance of the converter by adding graphite particles to both parts of the converter and creating a network of percolation paths for water ions and electrons made it possible to increase the open-circuit voltage to 0.16 V, reduce the internal resistance to 120 Ohm and increase the power to 56 mu W (4.7 mu W/cm2).

In this work, the influence of additives of rare earth and transition metals on the process of formation of the structure, mechanical and electrical properties of the SOFC electrolyte material based on zirconia was studied in order to identify the key technological and physical parameters affecting this process.A strong influence of the type of doping impurity on the lattice parameter of synthesized particles and sintered ceramics, on the strength and density of ceramics, and on the activation energy of ionic conductivity along grain boundaries was found. The effect of the type of additive on the value of ionic conductivity by grain volume in sintered ceramics was not detected.It was shown that the dopants effects on the ionic conductivity of zirconia electrolyte material in the indirect mode. The ionic radius of the dopants are determines the level of stability of the substitutional solid solution, and the diffusion of the impurity to the grain boundaries during sintering. It has been established that the more the ionic radius of the impurity differs from the equivalent ionic radius of the cation, the greater the activation energy of ionic conductivity along grain boundaries is observed. This depends on the degree of contamination of the grain boundaries with various impurities, which can diffuse to the grain boundaries and segregate there due to a violation of the Hume-Rothery rule. At the same time, the activation energy of ionic conductivity over the grain volume changes insignificantly, which indicates that the conductivity over the grain volume depends strongly on the number of oxygen vacancies, the concentration of which weakly depends on the ionic radius of the impurity.

It was shown the forming of Ag-contained ZnO-CeO2 composites occurs due to the complex decomposition and structure transformation of oxide materials and Ag-complexes. It allows us to realise one synthesised approach for obtaining photosensitive materials with different particle sizes, defects and kinds of architecture. The possible mechanisms of photosensitivity of these materials are determined. For composite nanoparticles (NP) with sizes up to 30 nm, the photosensitivity is connected with an abnormal decrease of bandgap energies at reducing NP sizes and an effective charge separation due to electron stocks on [& Scy;& iecy;3+...O2] centres and surface [Ce4+...O2- ] oxidative centres formation. The appearance of the hyperfine structure pattern of six lines centred at g =2.002 and split by 93-94 G in the ESR spectra of the composite structure confirms the realization of this mechanism. For more big NP sizes of this composite, the surface plasmon resonance plays a more significant role in the material's photosensitive properties. The position of surface plasmon resonance depends on the kind of realised structure. The phase composition, temperature and reduction determine the type of structure (NPs/AgNPs ore core/Ag shell) that will be recognised in the Ag-contained CeO2-ZnO system.

The oxidation state of Fe, Cu, Eu, Ce, etc. in minerals is an important indicator of redox conditions for their formation and evolution. In this work, the features of X-ray emission Fe Lα,β spectra (XES) obtained by Cameca SX100 microprobe, as well as the Mössbauer spectra of Cr-spinels of various compositions from a number of the Urals ultramafic massifs, have been studied. Using microprobe data on the composition and homogeneity of the grains, as well as the Fe3+/\({\text{Fe}}_{{{\text{tot}}}}^{{{\text{M\"o ssb}}}},\) 19 intralaboratory reference samples have been selected from a large number of the Urals Cr-spinels. Based on the analysis of BSE images and maps of the distribution of elements in Cr-spinel grains, the most homogeneous ones were identified. It was shown that, up to the determination error, Fe3+/\({\text{Fe}}_{{{\text{tot}}}}^{{{\text{M\"o ssb}}}}\) coincides with that obtained in the framework for calculation approach based on microprobe data on the composition and assumptions about the mineral stoichiometry. For determination of Fe oxidation state by XES data, it has been proposed to use as a calibration dependence for intralaboratory reference samples the position of the maximum of Fe Lα line on the content of Fe2+; the latter is satisfactorily approximated by a linear function (rxy = 0.96); the relative error of Fe2+ determination is 2%. Approbation of the developed approach was carried out on a series of control samples of Cr-spinels; the obtained values of Fe2+ and Fe3+/Fetot agree satisfactorily with the Mössbauer and calculated data in the stoichiometric approximation.

The oxidation state of Fe, Cu, Eu, Ce, etc. in minerals is an important indicator of redox conditions for their formation and evolution. In this work, the features of X-ray emission Fe Lα,β spectra (XES) obtained by Cameca SX100 microprobe, as well as the Mössbauer spectra of Cr-spinels of various compositions from a number of the Urals ultramafic massifs, have been studied. Using microprobe data on the composition and homogeneity of the grains, as well as the Fe3+/\({\text{Fe}}_{{{\text{tot}}}}^{{{\text{M\"o ssb}}}},\) 19 intralaboratory reference samples have been selected from a large number of the Urals Cr-spinels. Based on the analysis of BSE images and maps of the distribution of elements in Cr-spinel grains, the most homogeneous ones were identified. It was shown that, up to the determination error, Fe3+/\({\text{Fe}}_{{{\text{tot}}}}^{{{\text{M\"o ssb}}}}\) coincides with that obtained in the framework for calculation approach based on microprobe data on the composition and assumptions about the mineral stoichiometry. For determination of Fe oxidation state by XES data, it has been proposed to use as a calibration dependence for intralaboratory reference samples the position of the maximum of Fe Lα line on the content of Fe2+; the latter is satisfactorily approximated by a linear function (rxy = 0.96); the relative error of Fe2+ determination is 2%. Approbation of the developed approach was carried out on a series of control samples of Cr-spinels; the obtained values of Fe2+ and Fe3+/Fetot agree satisfactorily with the Mössbauer and calculated data in the stoichiometric approximation.

We study the microstructure, strength, and micromechanisms of fracture of 50

This study is devoted to the development of new oxide materials and devices based on them for direct long-term production of electricity from ambient humidity, which can be used as an auxiliary power supply system for self-sufficient buildings. The simplest device, a tablet pressed from these powders, generates an electrical potential in the presence of a moisture gradient inside the sample. The output voltage level of the converter depends on the type of material and the porous structure of the converter. There is a dependence of the sign of the output voltage on the type of material, which can be related to the type and sign of the surface centers of the converter material particles. The main mechanism of the converter operation is the generation of the streaming potential during the movement of adsorbed moisture (water molecules) in the porous structure of the converter under the influence of the ambient air humidity gradient. An increase in converter thickness increases the generation time of the output voltage by up to several tens of hours, both with an increase and a decrease in the humidity level in the compartment. The results of this study will help to use a huge reservoir of low-potential energy contained in gaseous water molecules to generate "green" electricity.

The present contribution is aimed to identify the microstructure of zirconia ceramics possessing the higher fracture toughness. 3D-FE-simulations of indentation testing with taking into account damage evolution in the cut-out of a microstructure have been performed in ZrO 2 -ceramics by using the FEM-Software ABAQUS CAE. We have performed the simulation of failure behavior of ZrO 2 -ceramics, considering the crack propagation both in the interior of grains (with Element Elimination Technique) as well as in grain boundaries (with Cohesive Zone Modeling approach of two different micro-structures. The constitutive behavior of the grains has been considered to be orthotropic elastic. The performed simulations could serve as an example of the solution of specific multiscale fracture mechanical problem and its application to design of materials.

This study is devoted to creating media for the accumulation of electrical energy based on zirconia nanoparticles. The effect of charge accumulation by compacted zirconia nanoparticles, the manifestation of which depends on the size of the particles and the degree of hydration of their surface, was found. It is shown that for the system of hydrated nanoparticles, the formation of the dielectric constant of the entire structure as a whole is influenced by the dielectric properties of the nanoparticle materials and water on its surface. The difference in the dielectric properties of the filler (water) and the matrix (material of zirconia nanoparticles) leads to a strong increase in the dielectric constant of hydrated compacted nanoparticles due to the Maxwell–Wagner effect, which is a promising application in the development of energy storage media. Graphical abstract

The current transfer through a two-layer structure saturated with absorbed water, each layer of which consists of pressed ZrO2 nanoparticles with two sizes (10 and 20 nm), has been studied. The structure was obtained using the isostatic pressing the ZrO2 + H2O powders. The form of current–voltage characteristics inherent to the studied structure, that has diode properties with the rectification coefficient close to 3, has been explained by the appearance of a potential barrier at the interlayer boundary.

The effect of particle size on the dominant densification mechanism at the initial stage of sintering of tetragonal zirconia nanoparticles was investigated. It has been found that a decrease in the particle size of zirconia leads to a change in the diffusion mechanism. The volume diffusion mechanism identified by the value of densification parameter n = 0.5 was dominant in zirconia nanoparticles with the average particle size 32 and 26.2 nm. The grain-boundary diffusion mechanism (n = 0.3) dominated during the sintering zirconia nanoparticles with the average particle size 21.7 nm. It was established that the change in densification parameter n from 0.5 to 0.3 caused by the increase in the value of particle surface to volume ratio due to the particles size decrease from 32 to 21 nm. A further decrease in the particle size to 17–12 nm led to a decrease in the densification parameter n to 0.17–0.11, respectively. This may be due to an increase in the influence of the particle surface on the sintering process (large values of particle surface to volume ratio) and, accordingly, the action of the surface diffusion mechanism.

The engineering of doped zirconia nanoparticles (NPs) for energy application is realized in concept Research Smart Laboratory. To improve nanomaterials’ engineering, correlations of “salt concentration—powder dispersity” and “calcined temperature—particle’s sizes” were built. The correlation of “materials structure—materials functionality” is made. The technology forming ceramics with varying grain sizes and densities under the same thermodynamic conditions (1350 °C) from NPs with different sizes is developed. The impedance spectroscopy with the distribution of relaxation time analysis is used for ionic conductivity ceramic investigation in range 240–900 °C. The activation energies of the grain and grain boundary oxygen diffusion are calculated. It was shown that the energy activation of bulk oxygen diffusion does not depend on ceramic grain size (Ea = 0.9 eV). The energies activation of grain boundary oxygen diffusion estimated in the framework of the bricklayer model show a weak growth with the rising of ceramic grains sizes. The values of the volume activation energy are close to the grain-boundary activation energy for ceramics obtained from nanoparticles smaller than 18 nm. It was found that the grain boundary space contains two types of elements with different geometries. The size of NPs used for ceramic determines the size of grain boundaries elements. It was shown that the density of sintered ceramic has a more substantial effect on its electrophysical properties than grain size. The NPs sizes of 18–24 nm are optimal for forming pressed powder compacts and sintered ceramics with high density.

Two series of ZrO2 samples—pure ZrO2 and ZrO2 doped by 3% of Y2O3—prepared at 400, 500, and 600 °C were studied. The samples were characterized by powder XRD, TEM, SANS, IR spectroscopy, and nitrogen adsorption at 77 K. Monoclinic ZrO2 was the dominating phase in the samples of pure zirconia, while Y-doped zirconia mainly consisted of tetragonal ZrO2. An increase in the calcination temperature led to the growth of the zirconia nanoparticle (NP) size and a decrease of the specific surface SBET. The size of Y-doped zirconia NPs (9–16 nm by XRD) was smaller compared to pure ZrO2 (12–19 nm), synthesized at the same temperatures. The content of the surface defects in the tetragonal Y-doped ZrO2 was estimated by analysis of IR spectra and other indicators and grew with the increase of the calcination temperature. The strength and content of the acidic surface sites were determined by potentiometric titration. The doping of ZrO2 by Y3+ led to the formation of the sites with lower pKa. The catalytic activity of ZrO2 and Y-doped ZrO2 in the reaction of α-tetralol oxidation by m-chloroperoxobenzoic acid was studied, and it was found that α-tetralone was the main product. The catalytic activity of the Y-doped zirconia samples in α-tetralol oxidation, expressed as conversion or turnover frequency (TOF) per 1 m2 or ZrO2, increased with the increase of the total concentration of the surface acidic centers.

This work is devoted to the demonstration of a real multifunctional material -zirconia based nanopowders, which can be used in the manufacture of various types of devices that convert natural energy sources into electricity (electrolyte and anode for SOFC, moisture-to-electricity converter). It was shown that such characteristics of nanopowders as parti-cle size, specific surface area, and type of surface centers, which depend on the temper-ature of nanopowder synthesis, could play both a positive and a negative role in the formation of the functional properties of a device. It was found that the synthesis of 8YSZ nanopowders at 700 degrees C is optimal for the manufacture of a dense electrolyte material and a porous SOFC anode material during sintering at 1400-1450 degrees C. The addition of a small amount of Al2O3 at the synthesis stage accelerates the sintering of the SOFC electrolyte material by 120 degrees C and leads to increasing the density to 97% of the theoretical value. The strength of the sintered anode material practically does not change after reduction in an atmosphere of N2-10% H2-5% CO2 and the value is 100 MPa. The synthesis temperature of 8YSZ nanopowder at 700 degrees C is also optimal for the manufacture of porous converters of ambient humidity into electricity. The formation of particles with a given size and type of surface centers allows generating an electric po- tential (100-200 mV) for hundreds of hours, which is 2-3 times higher than that of larger and smaller powders. The result of the work show that there are optimal conditions for the synthesis of powders (synthesis method, additives, synthesis temperature), as a result of which nanopowders are formed with characteristics (particle size, specific surface area, morphology) necessary and sufficient for the manufacture of several types of materials for devices of alternative energy. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

For the first time, shear-induced metallization on the (001) face of diamond single crystals of types Ib, IIa and IIb during hardness tests is studied. The tests are performed using the Vickers and Berkovich indenters on diamond single crystals grown by the temperature gradient method. In the Raman spectra of imprints obtained on the (001) face of diamond, intense photoluminescence bands with a complex shape are found, which complicates the identification of the phonon bands of the sp(2) phase of carbon. The sp(2) phase of carbon in the imprints on the (001) face is reliably revealed only for diamonds of type IIb and only in the case of using the Berkovich indenter. It is found that graphitization during hardness tests on the (001) face of diamond of type IIb is much less than on the (111) face. The recorded photoluminescence with a maximum at about 510 nm can be considered as evidence of the formation of the mixed sp(2)/sp(3) phase of amorphous carbon in the imprints on the (001) face of diamond in the initial stages of graphitization.

The properties of nanocrystalline powders of compositions (mol.%) 97 ZrO2–Y2O3, 95 ZrO2–3 Y2O3–2 CeO2, 92.5 ZrO2–2.5 Y2O3–5 CeO2, 90 ZrO2–2 Y2O3–8 CeO2, and 88 ZrO2–12 CeO2 were studied. The powders were produced by hydrothermal synthesis in an alkaline environment from a coprecipitated hydroxide mixture with a residual moisture of 15–20%. The powder properties were determined by X-ray diffraction (XRD), electron microscopy, BET, and petrography. Metastable F-ZrO2 was found to form in the hydrothermally synthesized powders. According to XRD, the F-ZrO2 → T-ZrO2 phase transformation began at 700°C and finished at 850–1000°C. The crystal optical characteristics of the powders indicate that the F-ZrO2 → T-ZrO2 phase transformation started at 400°C. The variations in F-ZrO2 and T-ZrO2 unit cell volumes are associated with lattice distortions under the action of different mechanisms in costabilization of the zirconia-based solid solution and with the ratio of Y2O3 and CeO2 in the solid solution. The tetragonality of the powders increases in the ZrO2 costabilization. The transformation strengthening mechanism for ceramics based on ZrO2 (Y2O3, CeO2) solid solutions becomes more effective with the formation of T-ZrO2, whose capability to the T-ZrO2 → M-ZrO2 phase transformation increases. The morphology of the powders varies topologically continuously, and the sizes of their primary particles hardly increase up to 1150°C. The variation in the specific surface area (from 153 to 2 m2/g) of the powders is determined by the F-ZrO2 → T-ZrO2 phase transformation and their sintering activity above 1000°C.

We study the influence of one-time reduction and redox cycling at 600°С in different hydrogencontaining media in the absence and in the presence of carbon dioxide on the strength and electric conductivity of ceramics of the ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 –NiO–CuO system with lowered Y 2 O 3 content and various ratios of the amounts of the ceramic and metallic phases. It is shown that cermets with different mass fractions of the nickel phase after reduction in pure hydrogen have high electric conductivity, which meets the requirements imposed on the anode materials. However, even in the absence of bulk microcracking, their strength after reduction becomes twice lower. The investigated ceramics in the initial state and cermets subjected to reduction at 600°С in different working media are characterized by the quasibrittle micromechanism of fracture. The redox treatment of cermets causes an insignificant increase in their electric conductivity but guarantees the level of strength close to the strength of the original ceramics, i.e., proves to be an efficient technology for improving the physicomechanical properties of Ni-containing anodes of solid-oxide fuel cells, including the case where CO 2 impurities are present in the working medium.

We report structural and luminescence properties of the spinel MgAl2O4:Sm3+ nanophosphors (with Sm3+ content of 0.03, 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, and 3.0 wt%.) synthesized by a co-precipitation method. The X-ray phase analysis and transmission electron microscopy show that the size of the MgAl2O4:Sm3+ nanoparticles varies from 5 nm to 6 nm at a synthesis temperature of 700 degrees C and from 7 nm to 15 nm at 1000 degrees C. We demonstrate that the samples synthesized at 700 degrees C with a samarium content of 1.5 wt% are the most promising candidates for use as orange phosphors. We show that near-surface rare-earth ion segregation arises in the nanoparticles with an average size of 10 nm and the Sm concentrations of 1.0 wt% and 1.5 wt%. Simulation of the MgAl2O4:Sm3+ luminescence spectrum by the modified crystal field theory (MCFT) indicates that Sm ions occupy both octahedral and tetrahedral positions. Complexes with broken bonds, non-equivalent bonds, and complexes with vacancies are revealed and confirmed by EPR studies and theoretical calculations. We demonstrate that the most intense transitions arise in tetrahedral and octahedral complexes with vacancies. The enhancement of the emission efficiency caused by the distortions of the Sm3+ coordination complexes competes with the luminescence quenching caused by surface segregation.

Small‐scaled non‐standard specimens with chevron notch (CN) from Zirconia ceramics are probed both numerically and experimentally by wedging. The original construction in the form of double cantilever beam (DCB) with CN is considered for the fracture toughness determination of ZrO2 specimens. The fracture toughness is determined in experiment on wedging of DCB with CN, with application of analytical formula derived by one of the authors and maximum force, bending the cantilever's arm. The 3D finite‐element simulations of wedge splitting test are performed using two approaches: cohesive zone modeling (CZM) approach and element elimination technique (EET). The specific fracture energy defined in experiments is taken as the input parameter for CZM simulations of crack propagation. The effect of parameters, namely, cohesive strength, and friction coefficient, between ceramic wedge and ceramic cantilever, is considered. Different traction–separation laws are implemented, and the resulting force–displacement curves are compared with experimentally obtained ones. In the CZM approach, considering the fracture energy and the predefined crack path, matching of experimental and numerical results is not achieved. In EET, in which the restrictions on the crack paths and the requirements for inputting the fracture energy are not imposed, a good match with the experimental results is achieved.

We study the regularities of changes in the microstructure, strength, electric conductivity, and micromechanism of fracture of 50% (ZrO2–8 mole% Y2O3–2 wt.% Al2O3) + 50% (NiO–5 wt.% CuO) ceramics and the corresponding cermet [intended for manufacturing of the anodes (substrates) in solid-oxide fuel cells] caused by reduction in high-temperature (600°С) Ar–5% H2 and N2–10% H2–5% CO2 gas mixtures. It is shown that the investigated cermet has a higher strength and electric conductivity if the calcination temperature of the initial powders is lowered from 900°С to 700°С and their sintering temperature is lowered from 1450°С to 1400°С. The signs of pollution of this material with carbon compounds were not detected. We also did not reveal any decrease in its strength and electric conductivity after reduction carried out at 600°С in a N2–10% H2–5% CO2 gas mixture as compared to the characteristics of the same material reduced in an Ar–5% H2 mixture.