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A quantum theory of spin dynamics in the rare-earth orthoferrites excited by terahertz laser pulses is developed. The study demonstrates that dynamic magnetic configurations, triggered by a light pulse, exhibit stability even after the excitation source is ceased. The magnitude of post-excitation oscillations is linked to the ratio between the frequency of rare-earth ion excitations and the frequency of the external source. According to the analysis presented, dynamic response is significantly amplified when the system is exposed to ultrashort terahertz pulses. The physical characteristics of the oscillations emerging after the pulse are determined, and the factors governing their amplitude and phase are identified. The response signal is found to be dependent on the initial part of the pulse, specifically the half-period of the ultrashort light wave, while the subsequent part of the pulse contributes minimally to post-pulse magnetization dynamics. The findings highlight that in DyFeO 3 , terahertz dynamics primarily result from the influence of the magnetic field of the light, leading to excitations of electrons from the ground state to low-lying electronic levels of Dy 3+ ions. Additionally, the dynamic magnetoelectric effect excited by the electric field of the pulse is explored, revealing the emergence of odd magnetic modes., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

We report the results of synthesis of zinc selenide (ZnSe) nanocrystals into SiO 2 /Si track templates formed by irradiation with 200 MeV Xe ions up to a fluence of 10 7 ions/cm 2 . Zinc selenide nanocrystals were obtained by chemical deposition from the alkaline aqueous solution. Scanning electron microscopy, X-ray diffractometry, Raman and photoluminescence spectroscopy, and electrical measurements were used for characterization of synthesized ZnSe/SiO 2nanoporous /Si nanocomposites. XRD data for as-deposited precipitates revealed the formation of ZnSe nanocrystals with cubic crystal structure, spatial syngony F-43m (216). According to non-empirical calculations using GGA-PBE and HSE06 functionals, ZnSe crystal is a direct-zone crystal with a minimum bandgap width of 2.36 eV and anisotropic electronic distribution. It was found that a thermal treatment of synthesized nanocomposites at 800 °C results in an increase in ZnSe nanocrystallites size as well as an increase in emission intensity of created precipitates in a broad UV-VIS spectra range. However, vacuum conditions of annealing still do not completely prevent the oxidation of zinc selenide, and a formation of hexagonal ZnO phase is registered in the annealed samples. The current-voltage characteristics of the synthesized nanocomposites proved to have n-type conductivity, as well as increased conductivity after annealing.

This study presents theoretical and experimental investigations into the electron and hole color centers in BaFBr crystals, characterizing their electronic and optical properties. Stoichiometric BaFBr crystals grown by the Steber method were used in the experiments. Radiation defects in BaFBr crystals were created by irradiation with 147 MeV 84 Kr ions with up to fluences of 10 10 -10 14 ions/cm 2 . The formation of electron color centers (F(F - ), F 2 (F - ), F 2 (Br - )) and hole aggregates was experimentally established by optical absorption spectroscopy. Performed measurements are compared with theoretical calculations. It allows us to determine the electron transition mechanisms and investigate the processes involved in photoluminescence emission in Eu-doped BaFBr materials to enhance the understanding of the fundamental electronic structure and properties of electron and hole color centers formed in BaFBr crystals.

By using DFT simulations employing the GGA/PBE and LDA/CA-PZ approximations, the effects of the Hubbard U correction on the crystal structure, electronic properties, and chemical bands of the cubic phase ( P m3¯m) of STO were investigated. Our findings showed that the cubic phase ( P m3¯m) STO's band gaps and lattice parameters/volume are in reasonably good accordance with the experimental data, supporting the accuracy of our model. By applying the DFT + U method, we were able to obtain band gaps that were in reasonably good agreement with the most widely used experimental band gaps of the cubic ( P m3¯m) phase of STO, which are 3.20 eV, 3.24 eV, and 3.25 eV. This proves that the Hubbard U correction can overcome the underestimation of the band gaps induced by both GGA/PBE and LDA/CA-PZ approximations. On the other hand, the Sr-O and Ti-O bindings appear predominantly ionic and covalent, respectively, based on the effective valence charges, electron density distribution, and partial density of states analyses. In an attempt to enhance the performance of STO for new applications, these results might also be utilized as theoretical guidance, benefitting from our precise predicted values of the gap energies of the cubic phase ( P m3¯m).

We investigated the electronic structure of Mg-, Si-, and Zn-doped four-faceted [001]- and [110]-oriented SnO 2 nanowires using first-principles calculations based on the linear combination of atomic orbitals (LCAO) method. This approach, employing atomic-centered Gaussian-type functions as a basis set, was combined with hybrid density functional theory (DFT). Our results show qualitative agreement in predicting the formation of stable point defects due to atom substitutions on the surface of the SnO 2 nanowire. Doping induces substantial atomic relaxation in the nanowires, changes in the covalency of the dopant-oxygen bond, and additional charge redistribution between the dopant and nanowire. Furthermore, our calculations reveal a narrowing of the band gap resulting from the emergence of midgap states induced by the incorporated defects. This study provides insights into the altered electronic properties caused by Mg, Si, and Zn doping, contributing to the further design of SnO 2 nanowires for advanced electronic, optoelectronic, photovoltaic, and photocatalytic applications.

This study introduces an innovative method for synthesizing Cadmium Oxide /Cadmium Sulfide/Zinc Oxide heterostructures (CdO/CdS/ZnO), emphasizing their potential application in solar energy. Utilizing a combination of electrochemical deposition and oxygen annealing, the research provides a thorough analysis of the heterostructures through scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) spectroscopy. The findings reveal a complex surface morphology and a composite structure with significant contributions from hexagonal CdS and cubic CdO phases. The study highlights the uniformity in the distribution of luminescent centers and the crystalline quality of the heterostructures, which is evident from the PL analysis. The redshift observed in the emission peak and the additional peaks in the excitation spectrum indicate intricate optical properties influenced by various factors, including quantum confinement and lattice strain. The research demonstrates these heterostructures' potential in enhancing solar cells' efficiency and applicability in optoelectronic devices. This comprehensive characterization and analysis pave the way for future optimization and application in efficient and sustainable solar energy solutions.

Samples of ZrO 2 ceramics with different concentrations of impurity titanium ions were synthesized by mixing zirconium and titanium oxide powders in different mass ratios. The X-ray diffraction analysis was used to determine the phase composition, lattice parameters, and crystallite size of the ceramics with varying dopant concentrations. Upon irradiation of the samples with 220 MeV Xe ions to a fluence of 10 10 ions/cm 2 , a decrease in the intensity of the pulsed cathodoluminescence band at 2.5 eV was observed. Additionally, ion irradiation resulted in the emergence of a new thermoluminescence peak at 450-650 K attributed to radiation-induced traps of charge carriers. Further analysis revealed that the thermoluminescence curves of samples irradiated with electrons and ions comprise a superposition of several elementary peaks. Notably, a complex non-monotonic dependence of cathodo- and thermoluminescence intensity on titanium concentration was observed, suggesting the influence of concentration quenching and the presence of tunneling transitions.

Electrochemical deposition into a prepared SiO 2 /Si-p ion track template was used to make orthorhombic SnO 2 vertical nanowires (NWs) for this study. As a result, a SnO 2 -NWs/SiO 2 /Si nanoheterostructure with an orthorhombic crystal structure of SnO 2 nanowires was obtained. Photoluminescence excited by light with a wavelength of 240 nm has a low intensity, arising mainly due to defects such as oxygen vacancies and interstitial tin or tin with damaged bonds. The current-voltage characteristic measurement showed that the SnO 2 -NWs/SiO 2 /Si nanoheterostructure made this way has many p-n junctions.

The aim of this study is to comprehensively examine the structural composition and properties of the AgAlS 2 crystal during its high-pressure phase. This analysis delves into the second coordination environment of the crystal structure and elucidates the distinct transformations it undergoes during the phase transition. The band energy structure was calculated, and the origin of electronic levels was clarified. It is shown that the crystal becomes non-stratified during the phase transition. This study also determined the values of the crystal's carrier effective masses, underscoring its spatial anisotropy. It was found that the calculated optical functions are similar to the crystal in the chalcopyrite structure, and their differences are shown. Further, this study involved the calculation of the crystal's phonon spectrum, revealing the spectrum's transformation during the phase transition. The vibrational frequencies were also obtained, with a symmetrical classification of vibrational modes. Finally, this study derived the infrared and Raman spectra of the AgAlS 2 crystal, thereby providing a comprehensive picture of the crystal during its high-pressure phase.

The synthesis of β-Ga 2 O 3 ceramic was achieved using high-energy electron beams for the first time. The irradiation of gallium oxide powder in a copper crucible using a 1.4 MeV electron beam resulted in a monolithic ceramic structure, eliminating powder particles and imperfections. The synthesized β-Ga 2 O 3 ceramic exhibited a close-to-ideal composition of O/Ga in a 3:2 ratio. X-ray diffraction analysis confirmed a monoclinic structure (space group C2/m) that matched the reference diagram before and after annealing. Photoluminescence spectra revealed multiple luminescence peaks at blue (~2.7 eV) and UV (3.3, 3.4, 3.8 eV) wavelengths for the synthesized ceramic and commercial crystals. Raman spectroscopy confirmed the bonding modes in the synthesized ceramic. The electron beam-assisted method offers a rapid and cost-effective approach for β-Ga 2 O 3 ceramic production without requiring additional equipment or complex manipulations. This method holds promise for fabricating refractory ceramics with high melting points, both doped and undoped.

In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: transmission spectra in the IR region (190-7000) nm, optical absorption spectra in the range (1.2-6.5) eV, and Raman spectra were measured along the depth of ion penetration from the surface to 30 µm. A peak with a broad shape at approximately 5.3 eV can be observed in the optical absorption spectrum of irradiated spinel crystals. This band is linked to the electronic color centers of F + and F. Meanwhile, the band with a maximum at ~(3-4) eV is attributed to hole color centers. Apart from the typical Raman modes of an unirradiated crystal, additional modes, A1g* (720 cm -1 ), and Eg* (385 cm -1 ), manifested mainly as an asymmetric shoulder of the main Eg mode, are also observed. In addition, the Raman spectroscopy method showed that the greatest disordering of crystallinity occurs in the near-surface layer up to 4 μm thick. At the same time, Raman scattering spectroscopy is sensitive to structural changes almost up to the simulated value of the modified layer, which is an excellent express method for certifying the structural properties of crystals modified by swift heavy ions.

The purpose of this study is to comprehensively analyze the influence of different fluences of irradiation with Xe 23+ heavy ions on alterations in the structural, optical, and strength properties of AlN ceramics and to establish a connection between structural distortions and alterations in the optical and mechanical properties of the ceramics. X-ray diffraction, UV-Vis and Raman spectroscopy, and indentation and single-compression methods were used as research methods. During the study, it was demonstrated that at low irradiation fluences, the main role in the changes in the properties of the AlN ceramics is played by effects related to changes in their optical properties and a fundamental absorption edge shift, which characterizes changes in the electronic properties of the ceramics (changes in the distribution of electron density). A study of the variations in the optical properties of the examined samples in relation to the irradiation fluence showed that when the fluence surpasses 5 × 10 11 ion/cm 2 , an extra-spectral absorption band emerges within the range of 3.38-3.40 eV. This band is distinctive for the creation of vacancy O N - V Al complexes within the damaged layer's structure. The presence of these complexes signifies structural deformations and the accumulation of defective inclusions within the damaged layer. An analysis of changes in the parameters of the crystal lattice showed that structural distortions in the damaged layer are due to the accumulation of tensile residual mechanical stresses, an increase in the concentration of which leads to the swelling and destruction of the damaged layer. Some correlations between the mechanical properties of ceramics and the irradiation fluence indicate the ceramics' remarkable resistance to radiation-induced brittleness and weakening. These effects become apparent only when structural damage accumulates, resulting in the swelling of the crystal lattice exceeding 2.5-3%., Competing Interests: The authors declare no conflict of interest.

Overweight and obesity is a multifactorial, multisystem disease declared a global epidemic by the World Health Organization (WHO) as early as in 1997. At least 30% of the working-age population in Russia is overweight. Only the use of physical activity as an integral (basic) part of obesity treatment and maintenance of the body weight achieved in the course of treatment can achieve durable and long-lasting treatment results as well as significant changes in the body structure (fat/non-fat body weight ratio). Terrainkur (therapeutic walking) is a method of spa treatment that combines climatotherapy and physical therapy. One of the problems in physical activity in obese people is the difficulty they experience in exercising due to the impaired walking pattern caused by imbalances in the muscle chains, including pelvic region, cervical region, which reduces endurance and commitment to physical activity. The study found that the exposure group (Terrainkur) showed lower values of "total fat", "metabolic age", "basic caloric value" compared to initial results and the control group; the exposure group (Terrainkur) showed a decrease in the deviation of the centre of body axis projection from the proper axis, the percentage of non-compliance with the proper fluctuations of the foot underextension. These changes contributed to the elimination of terrainkur restrictions and, as a result, improved the patient compliance during the terrainkur exercises.

The aim of this paper is to test the previously stated hypothesis and several experimental facts about the effect of the ion flux or ion beam current under irradiation with heavy ions on the radiation damage formation in the ceramic near-surface layer and their concentration. The hypothesis is that, when considering the possibilities of using ion irradiation (usually with heavy ions) for radiation damage simulation at a given depth, comparable to neutron irradiation, it is necessary to consider the rate factor for the set of atomic displacements and their accumulation. Using the methods of X-ray diffraction analysis, Raman and UV-Vis spectroscopy, alongside photoluminescence, the mechanisms of defect formation in the damaged layer were studied by varying the current of the Xe 23+ ion beam with an energy of 230 MeV. As a result of the experimental data obtained, it was found that, with the ion beam current elevation upon the irradiation of nitride ceramics (AlN) with heavy Xe 23+ ions, structural changes have a pronounced dependence on the damage accumulation rate. At the same time, the variation of the ion beam current affects the main mechanisms of defect formation in the near-surface layer. It has been found that at high values of flux ions, the dominant mechanism in damage to the surface layer is the mechanism of the formation of vacancy defects associated with the replacement of nitrogen atoms by oxygen atoms, as well as the formation of ON-VAl complexes.

Bronchial asthma (BA) is a common disease that contributes significantly to the incidence rate and death rate worldwide. A widespread treatment method is the use of inhalations of mineral waters, with conflicting information about their effectiveness. Purpose of the study was to assess the generalized effect power of the course of inhalations of mineral waters on the disease progress in patients with BA. A search of randomized clinical studies in data bases Pubmed, EMBASE, ELibrary, MedPilot amd CyberLeninka, according to PRISMA strategy, published between 1986 and July 2021. Standardized difference of mean values and their 95% of CI were employed for calculation using the random effects model. The meta-analysis drawing on 1266 sources included 14 studies, with 2 of them being randomized controlled clinical studies, including the results of the treatment of 525 patients. All 14 articles contain a conclusion that the inhalation of mineral water has a positive effect on the course of the disease in patients with BA. The analysis demonstrated that the group of patients after mineral water inhalations, compared with the control group, showed improvement of forced expiratory volume (FEV1), expressed both in % of the norm and in liters. The standardized difference of mean values FEV1 (%) (Hedge's g) was 8.2 (95% CI: 5.87 - 10.59; 100%), FEV1 values (liter.) (Hedge's g) was 0.69 (95% CI: -0.33-1.05). A significant heterogeneity of the results of individual studies was found (Q=124.96; tau2 = 14.55, I2 = 69.13%, p<0.0001 and Q=2.35; tau2 = 0, I2 = 0%, p<0.0001). Patients with mild, moderate, and hormone-dependent BA with a controlled and partially controlled disease course, after mineral water inhalations, compared with the control group, demonstrated a statistically significant decrease in the frequency and intensity of the cardinal symptoms of BA and improvement of FEV1.

We have performed a systematic study resulting in detailed information on the structural, electronic and optical properties of the cubic ( P m3¯m) and tetragonal ( P 4mm) phases of PbTiO 3 applying the GGA/PBE approximation with and without the Hubbard U potential correction. Through the variation in Hubbard potential values, we establish band gap predictions for the tetragonal phase of PbTiO 3 that are in rather good agreement with experimental data. Furthermore, the bond lengths for both phases of PbTiO 3 were assessed with experimental measurements, confirming the validity of our model, while chemical bond analysis highlights the covalent nature of the Ti-O and Pb-O bonds. In addition, the study of the optical properties of the two phases of PbTiO 3 , by applying Hubbard' U potential, corrects the systematic inaccuracy of the GGA approximation, as well as validating the electronic analysis and offering excellent concordance with the experimental results. Therefore, our results underline that the GGA/PBE approximation with the Hubbard U potential correction could be an effective method for obtaining reliable band gap predictions with moderate computational cost. Therefore, these findings will enable theorists to make use of the precise values of these two phases' gap energies to enhance PbTiO 3 's performance for new applications.

In this work, we present the results of the structure and luminescence properties of YAG:Ce (Y 3 Al 5 O 12 doped with Ce 3+ ions) ceramic samples. Their synthesis was carried out by sintering samples from the initial oxide powders under the powerful action of a high-energy electron beam with an energy of 1.4 MeV and a power density of 22-25 kW/cm 2 . The measured diffraction patterns of the synthesized ceramics are in good agreement with the standard for YAG. Luminescence characteristics at stationary/time-resolved regimes were studied. It is shown that under the influence of a high-power electron beam on a mixture of powders, it is possible to synthesize YAG:Ce luminescent ceramics with characteristics close to the well-known YAG:Ce phosphor ceramics obtained by traditional methods of solid-state synthesis. Thus, it has been demonstrated that the technology of radiation synthesis of luminescent ceramics is very promising.

Recently gallium oxide ([Formula: see text]) has become one of the most actively studied materials due to its competitive electronic properties such as wide bandgap, high breakdown field, simple control of carrier concentration, and high thermal stability. These properties make gallium oxide a promising candidate for potential applications in high-power electronic devices. [Formula: see text]-[Formula: see text] crystals are commonly grown by the Czochralski method in an iridium (Ir) crucible. For this reason, Ir is often present in [Formula: see text] crystals as an unintentional dopant. In this work the impact of Ir incorporation defects on potential p-type conductivity in [Formula: see text]-[Formula: see text] is studied by means of density functional theory. The metastable [Formula: see text]-[Formula: see text] phase was investigated as the model object to understand the processes caused by iridium doping in gallium oxide-based systems. Obtained results allow us to understand better the influence of Ir on [Formula: see text] electronic structure, as well as provide interpretation for optical transitions reported in recent experiments., (© 2023. The Author(s).)

The purpose of this paper is to study the effect of PbO doping of multicomponent composite glass-like ceramics based on TeO 2 , WO 3 , Bi 2 O 3 , MoO 3 , and SiO 2 , which are one of the promising materials for gamma radiation shielding. According to X-ray diffraction data, it was found that the PbO dopant concentration increase from 0.10 to 0.20-0.25 mol results in the initialization of the phase transformation and structural ordering processes, which are expressed in the formation of SiO 2 and PbWO 4 phases, and the crystallinity degree growth. An analysis of the optical properties showed that a change in the ratio of the contributions of the amorphous and ordered fractions leads to the optical density increase and the band gap alteration, as well as a variation in the optical characteristics. During the study of the strength and mechanical properties of the synthesized ceramics, depending on the dopant concentration, it was found that when inclusions in the form of PbWO 4 are formed in the structure, the strength characteristics increase by 70-80% compared to the initial data, which indicates the doping efficiency and a rise in the mechanical strength of ceramics to external influences. During evaluation of the shielding protective characteristics of the synthesized ceramics, it was revealed that the formation of PbWO 4 in the structure results in a rise in the high-energy gamma ray absorption efficiency.

Indium tin oxide thin films were deposited by magnetron sputtering on ceramic aluminum nitride substrates and were annealed at temperatures of 500 °C and 600 °C. The structural, optical, electrically conductive and gas-sensitive properties of indium tin oxide thin films were studied. The possibility of developing sensors with low nominal resistance and relatively high sensitivity to gases was shown. The resistance of indium tin oxide thin films annealed at 500 °C in pure dry air did not exceed 350 Ohms and dropped by about 2 times when increasing the annealing temperature to 100 °C. Indium tin oxide thin films annealed at 500 °C were characterized by high sensitivity to gases. The maximum responses to 2000 ppm hydrogen, 1000 ppm ammonia and 100 ppm nitrogen dioxide for these films were 2.21 arbitrary units, 2.39 arbitrary units and 2.14 arbitrary units at operating temperatures of 400 °C, 350 °C and 350 °C, respectively. These films were characterized by short response and recovery times. The drift of indium tin oxide thin-film gas-sensitive characteristics during cyclic exposure to reducing gases did not exceed 1%. A qualitative model of the sensory effect is proposed.

The ESR spectra of nanostructured samples of monoclinic ZrO 2 irradiated by electrons with energies of 130 keV, 10 MeV, and by a beam of Xe ions (220 MeV) have been studied. It has been established that irradiation of samples with electrons (10 MeV) and ions leads to the formation of radiation-induced F + centers in them. Thermal destruction of these centers is observed in the temperature range of 375-550 K for electron-irradiated and 500-700 K for ion-irradiated samples. It is shown that the decrease in the concentration of F + centers is associated with the emptying of traps responsible for thermoluminescence (TL) peaks in the specified temperature range. In the samples irradiated with an ion beam, previously unidentified paramagnetic centers with g = 1.963 and 1.986 were found, the formation of which is likely to involve Zr 3+ ions and oxygen vacancies. Thermal destruction of these centers occurs in the temperature range from 500 to 873 K., Competing Interests: The authors declare no conflict of interest

The paper studies the effect of Li 2 SiO 3 /Li 4 SiO 4 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 Li 2 SiO 3 phase, and the main phase in ceramics is the monoclinic Li 4 SiO 4 phase. An analysis of the morphological features of the synthesized ceramics showed that an increase in the Li 2 SiO 3 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 Li 2 SiO 3 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.

This article considers the effect of MoO 3 and SiO additives in telluride glasses on the shielding characteristics and protection of electronic microcircuits operating under conditions of increased radiation background or cosmic radiation. MoO 3 and SiO dopants were chosen because their properties, including their insulating characteristics, make it possible to avoid breakdown processes caused by radiation damage. The relevance of the study consists in the proposed method of using protective glasses to protect the most important components of electronic circuits from the negative effects of ionizing radiation, which can cause failures or lead to destabilization of the electronics. Evaluation of the shielding efficiency of gamma and electron radiation was carried out using a standard method for determining the change in the threshold voltage (∆U) value of microcircuits placed behind the shield and subjected to irradiation with various doses. It was established that an increase in the content of MoO 3 and SiO in the glass structure led to an increase of up to 90% in the gamma radiation shielding efficiency, while maintaining the stability of microcircuit performance under prolonged exposure to ionizing radiation. The results obtained allow us to conclude that the use of protective glasses based on TeO 2 -WO 3 -Bi 2 O 3 -MoO 3 -SiO is highly promising for creating local protection for the main components of microcircuits and semiconductor devices operating under conditions of increased background radiation or cosmic radiation.

The atomic structure of antiphase boundaries in Sr-doped lanthanum scandate (La 1- x Sr x ScO 3- δ ) perovskite, promising as the proton conductor, was modelled by means of DFT method. Two structural types of interfaces formed by structural octahedral coupling were constructed: edge- and face-shared. The energetic stability of these two interfaces was investigated. The mechanisms of oxygen vacancy formation and migration in both types of interfaces were modelled. It was shown that both interfaces are structurally stable and facilitate oxygen ionic migration. Oxygen vacancy formation energy in interfaces is lower than that in the regular structure, which favours the oxygen vacancy segregation within such interfaces. The calculated energy profile suggests that both types of interfaces are advantageous for oxygen ion migration in the material.

Herein we demonstrate the specifics of using the positron annihilation lifetime spectroscopy (PALS) method for the study of free volume changes in functional ceramic materials. Choosing technological modification of nanostructured MgAl 2 O 4 spinel as an example, we show that for ceramics with well-developed porosity positron annihilation is revealed through two channels: positron trapping channel and ortho-positronium decay. Positron trapping in free-volume defects is described by the second component of spectra and ortho-positronium decay process by single or multiple components, depending on how well porosity is developed and on the experimental configuration. When using proposed positron annihilation lifetime spectroscopy approaches, three components are the most suitable fit in the case of MgAl 2 O 4 ceramics. In the analysis of the second component, it is shown that technological modification (increasing sintering temperature) leads to volume shrinking and decreases the number of defect-related voids. This process is also accompanied by the decrease of the size of nanopores (described by the third component), while the overall number of nanopores is not affected. The approach to the analysis of positron annihilation lifetime spectra presented here can be applied to a wide range of functional nanomaterials with pronounced porosity.

First-principles density functional theory (DFT) is employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga 2 O 3 crystals. Hybrid exchange-correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga 2 O 3 . Based on the results of our calculations, we predict that an oxygen vacancy in β-Ga 2 O 3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga 2 O 3 . On the other hand, all types of charge states of gallium vacancies are sufficiently deep acceptors with transition levels more than 1.5 eV above the valence band of the crystal. Due to high formation energy of above 10 eV, they cannot be considered as a source of p-type conductivity in β-Ga 2 O 3 .