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Cationic ion-conductors have found wide practical application as electric batteries. Among them the lithium-ion batteries are the most common commercially used. However, research is being actively carried out to improve the safety of these batteries. Among the possible compounds, silver-containing phases are attractive, since silver-ions, along with high values of ionic conductivity in solid-state, haven’t high chemical activity like the same alkali metal-ions. Realization of the crystal structure necessary for effective ion transport is observed in compounds of the argyrodite structure - a group of ternary chalcogenides and quaternary chalcohalogenides of multi-charged cations (Ge4+, Si4+, P5+). In this work, a study of heterovalent cationic P5+→Ge4+ substitution in the Ag8GeS6 enriched region was carried out. Single crystals of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions were grown by the method of directional crystallization using a solution-melt technique. The grown single crystals are characterized by the absence of macrodefects, a dark gray color with a metallic luster, and dimensions of l = ~3 cm and d = 1.2 cm. Using the Rietveld refinement method, the crystal structure was established and the lattice parameters of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions were determined. Established, that single crystals of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions crystallize in the orthorhombic crystal system in a primitive cell with space group Pna21. Keywords: argyrodites; single crystals; directional crystallization; phase analysis.

Ternary silver argyrodites exhibit a wide range of properties and are classified as promising solid-state conductors, thermoelectrics, photovoltaic and nonlinear optical materials. This is ensured by the peculiarity of the crystal structure of argyrodites, which combines a rigid anionic and a disordered cationic sublattice. This work is devoted to the development of a technological regime for growing high-quality single-crystalline samples of Ag7+x(P1-xGex)S6 (x = 0.1; 0.25; 0.33) solid solutions by the method of directed crystallization from the melt. Polycrystalline alloys of Ag7+x(P1-xGex)S6 (x = 0.1; 0.25; 0.33) solid solution were obtained from previously synthesized ternary Ag7PS6 and Ag8GeS6. The synthesis was carried out by a single-stage and single-temperature method at a maximum temperature of 1010°C. The phase composition of the synthesized alloys was determined by the XRD method. Phase analysis of the obtained polycrystalline alloys did not reveal reflections of impurity phases. The results of thermal studies of Ag7+x(P1-xGex)S6 alloys were used to develop a technological regime for single crystals growth. Ag7+x(P1-xGex)S6 single crystal was grown from the melt by the directional crystallization method. As a result of the research, high-quality single crystals of Ag7+x(P1-xGex)S6 solid solutions (x = 0.1; 0.25; 0.33) were obtained. According to the results of X-ray diffraction, it was established that the solid solution of the composition Ag7.1(P0.9Ge0.1)S6 crystallizes in the primitive cubic cell of SG P213, and the solid solutions Ag7.25(P0.75Ge0.25)S6 and Ag7.33(P0.67Ge0.33)S6 crystallizes in a metastable at room temperature high-temperature modification with SG F-43m. Keywords: argyrodites; single crystals; directional crystallization; phase analysis.

This work is devoted to the preparation of dense Ag+ conductive ceramic solid electrolytes in the Ag6PS5I‒Ag7GeS5I system and to the study of their electrical and optical properties. Using the non-destructive and simple method of optical diffuse reflectance spectroscopy, the value of the optical pseudogap energy of the Ag6+x(P1-xGex)S5I (x=0, 0.25, 0.5, 0.75, 1.0) solid solutions was obtained using the Kubelka-Munk function with the application of Tauc's graphic method. As a result of the performed mathematical analysis and graphic processing, it was established that the quaternary chalcohalogenides Ag6PS5I, Ag7GeS5I and solid solutions Ag6+x(P1-xGex)S5I (x=0.25, 0.5, 0.75) belong to direct-band semiconductors characterized by a forbidden optical transition . The study of electrical conductivity of Ag6+x(P1-xGex)S5I solid solutions (x=0, 0.25, 0.5, 0.75, 1.0) was carried out by the method of impedance spectroscopy, in the frequency 1×101–3×105 Hz and temperature 293–383 K ranges. For all ceramic materials prepared on the basis of Ag6+x(P1-xGex)S5I (x=0, 0.25, 0.5, 0.75, 1.0) solid solutions, an increase in the values of total electrical conductivity was observed, which is characteristic of materials with ionic electrical conductivity in the solid state. Keywords: argyrodites; solid solutions; ceramic; impedance spectroscopy; conductivity; optical properties; optical pseudogap.

Argyrodites are a class of compounds united by a similar structural motif. Typical for argyrodites is the coexistence of rigid anionic and disordered cationic sublattices. Due to this, argyrodites exhibit a wide range of properties. This work is devoted to the development of the single crystal growth regime of high-quality single-crystalline samples of Ag7PS6, which belongs to the compounds with argyrodite structure. The initial Ag7PS6 alloy is obtained from high purity elementary components by a two-step and one-temperature method. The maximum synthesis temperature was 850°C. The obtained alloy was investigated by DTA and XRD methods. The congruent melting of Ag7PS6 (Tmelt = 801°C) and the structural phase transition P213 → F-43m at a temperature of 271°C was confirmed. The study of the phase composition established the synthesized alloy is single-phase. The growth of Ag7PS6 was carried out by the directional crystallization method from the melt. The growth regime of Ag7PS6 was selected taking into account the nature of the thermal behavior of the compound based on DTA data. As a result, the grown Ag7PS6 single crystal of ~ 40 mm long and 12 mm in diameter was obtained. According to the results of XRD, it has been established that the grown Ag7PS6 single crystal is single-phase and crystallizes in a primitive cubic cell with lattice parameters of 10.3917 Å.

The possibility of combining different properties of materials within Ag – Sb – P – Se system prompted the study of the nature of physicochemical interactions in it. The main attention was paid to systems based on AgSbP2Se6 with the participation of stable binary and ternary compounds. It was assumed that the cross sections involving stable compounds would be quasi-binary. However, the nonquasibinarity of the sections Ag2Se – AgSbP2Se6 and Ag7PSe6– AgSbP2Se6 was proved, which indicated a complex interaction in the Ag – Sb – P – Se system. Difficulties were caused by the formation in the process of synthesis of multicomponent mixtures, the determination of the phase composition of which was complicated by the presence of reflexes on the powder patterns of different phases at the same angles. In this regard, it was expedient to summarize the experimental data on the nature of physicochemical interactions in the cross sections of the Ag – Sb – P – Se system. This would allow the establishment of quasi-binary, quasi-ternary and quasi-quaternary systems within the Ag – Sb – P – Se system, which was the aim of this work. It was established the nonquasibinarity of Ag7PSe6 – AgSbP2Se6 system. It intersects two quasi-ternary systems Ag4P2Se6 – AgSbSe2 – Se and Ag4P2Se6 – Sb2Se3 – Se. Other samples consist four-phases, in each of which, in addition to three complex compounds, selenium was detected. The quasiternary and quasiquaternary systems were formed by following quasibinaries: Ag7PSe6 – Ag4P2Se6, Ag7PSe6 – AgSbSe2, Ag7PSe6 – Se, Ag4P2Se6 – AgSbSe2, Ag4P2Se6 – Se, AgSbSe2 – Se, Ag4P2Se6 – Sb2Se3, AgSbSe2 – Sb2Se3, Sb2Se3 – Se, AgSbP2Se6 – Ag4P2Se6, AgSbP2Se6 – Sb2Se3, AgSbP2Se6 – Se. In the study of the cross section Ag2Se – AgSbP2Se6 it was found that it is also not quasi-binary and intersects one quasi-ternary (Ag7PSe6 – AgSbSe2 – Ag) and one quasi-binary system (Ag4P2Se6 - AgSbSe2). However, it is not taken into account that the Ag2Se – AgSbP2Se6 system also intersects the Ag4P2Se6 – Sb2Se3 system, which is quasi-binary. A refining analysis of the data confirmed that the cross section of Ag2Se - AgSbP2Se6 intersects the above quasi-ternary and two quasi-binary systems. In addition to the identified twelve, the study of the nature of the interaction in the cross sectionAg2Se – AgSbP2Se6 confirmed the quasibinarity of four systems (Ag7PSe6 – Ag2Se, Ag2Se – Ag, Ag2Se – AgSbSe2 and Ag – AgSbSe2) and additionally a system AgSbP2Se6 – Sb4(P2Se6)3. Thus, were established seventeen quasi-binary sections. It should be noted that some of them were known in the literature. Ag2Se – Ag and Sb2Se3 – Se systems are partial of the Ag – Se and Sb – Se systems, respectively, the Ag2Se – AgSbSe2 and AgSbSe2 – Sb2Se3 systems are subsystems of the quasi-binary Ag2Se – Sb2Se3 system. So, by fact thirteen quasi-binary systems in the quaternary system are established. It is noteworthy that the quaternary compound AgSbP2Se6 does not form quasi-binary systems with silver-containing complex compounds. The exception is Ag4P2Se6, which is often the final, occasionally intermediate product of the interaction of AgSbP2Se6 with other silver-containing compounds.

The mineral Ag8GeS6 is the first compound of a wide class of tetrahedrally close packed phases united by the common name argyrodites. Ternary argyrodites are complex chalcogenides formed on the basis of multi- and single-charged cations. Structural polyhedrons are tetrahedra formed on the basis of a multicharged cation and chalcogens, and the single-charged cations occupy the formed voids. Argyrodites belong to promising solid-state conductors and thermoelectric materials. This work is aimed to develop close to optimal conditions for single crystals growth of Ag8GeS6 by the method of directional crystallization from the melt. The initial Ag8GeS6 alloy was obtained using high purity elementary components by a two-stage single-temperature method. The congruent nature of the melting of Ag8GeS6 (Tmelt = 958°C) and the passage of the structural phase transition Pna21 → F-43m at a temperature of 227 ° C was confirmed by the DTA method. The Ag8GeS6 single crystal was grown from the melt by directional crystallization method. The growth regime of Ag8GeS6 was selected taking into account the nature of the thermal behavior of the compound based on DTA data. The grown single crystal of Ag8GeS6 is ~ 30 mm long and 12 mm in diameter and has a medium degree of cleavage. According to the results of XRD analysis, it was established that the obtained single crystalline sample of Ag8GeS6 is single-phase and crystallizes by low-temperature modification SG Pna21 with following lattice parameters: a = 15.147 Å, b = 7.469 Å, c = 10.584 Å.

This paper is aimed to the determination of the optical pseudogap values in phases with argyrodite structure by a simple method of diffuse reflectance spectroscopy. Samples of (Cu1-xAgx)7PSe6 (x = 0, 0.2, 0.3, 0.4, 0.6, 0.7, 0.9, 1.0) solid solutions were obtained in the form of microcrystalline powders by grinding in agate mortar. The diffuse reflectance spectra of the obtained (Cu1-xAgx)7PSe6 samples were studied in the spectral range 220–1400 nm (293 K) and analyzed using the Kubelka-Munk function. It was found that for (Cu1-xAgx)7PSe6 solid solutions the increase in the copper amount causes a shift of the beginning of the absorption edge to the region of higher energies. The optical pseudogap of (Cu1-xAgx)7PSe6 solid solutions was estimated by combining the Kubelka-Munch theory and the Tauc equation. It is established that the isovalent cationic substitution of Ag+ → Cu+ leads to a monotonic decrease in the values of the optical pseudogap, as a result, the compositional dependence of which is close to linear. This behavior of the optical pseudogap can only be associated with a decrease in the lattice parameters and characterizes the formation of solid solutions.

The present paper is devoted to the comparison of the determination methods of the optical pseudogap values of Ag7(Si1-xGex)S5I (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions by means of two optical spectroscopy techniques: optical absorption and diffuse reflection. Optical absorption spectroscopy was performed on thin single crystalline plane-parallel samples. Diffuse reflectance spectra were obtained on samples in the form of microcrystalline powders (~ 10–20 μm). The optical pseudogap values of Ag7(Si1-xGex)S5I solid solutions, determined on the basis of the logarithmic dependence of the absorption coefficient according to Urbach’s tail range and on the basis of the dependence of the Kubelka-Munk function using the Tauc method. It has been established that the pseudogap energies of the Ag7(Si1-xGex)S5I (x = 0; 0.2; 0.4; 0.6; 0.8; 1) solid solutions obtained by the analyzing the diffuse reflectance spectra of microcrystalline powders and spectral dependences of the absorption index for single crystals do not differ by more than 5% Therefore, it is correct to use a non-destructive and simple method of diffuse reflectance spectroscopy, to estimate the values of the optical pseudogap of porous, poly-, micro- and nanocrystalline objects.

Copper-containing compounds exhibit a wide range of properties, including thermoelectric, photoelectric, optical magnetic, superionic, superconducting, etc., which determines the areas of their practical use. In recent years, studies of complex copper selenides as promising thermoelectric (TE) materials have been actively carried out due to their advantages over traditional TE materials. Like binary Cu2Se, ternary selenides have low phonon thermal conductivity and high electrical conductivity and thermoelectric quality factor. Typically, copper-containing compounds belong to the p-type conductors and crystallize in four main structural types, among which phases with a diamond-like structure should be distinguished. Data on the nature of physicochemical interaction in the Cu – Sn – Se system are limited and contradictory. In view of this, it is important to carry out the triangulation of the ternary system Cu–Sn–Se, which is the first stage of the study of multicomponent systems. The investigated alloys of the Cu – Sn – Se system were obtained by fusing elementary components of high purity in vacuum quartz ampoules. The obtained alloys were investigated using X-ray powder diffraction (XRD) and differential thermal (DTA) analyzes. At the temperature of homogenizing annealing (170 ° С) there are seven binary Cu2Se, CuSe, CuSe2, Cu6Sn5, Cu3Sn, SnSe, SnSe2 and one ternary phase Cu2SnSe3 stable in the Cu – Sn – Se ternary system. The existence of the ternary phase of Cu2SnSe4 has not been confirmed, because the alloy corresponding to its stoichiometric composition is a mixture of Cu2SnSe3 and Se. To establish quasibinary sections of the Cu – Sn – Se system were performed the synthesis and phase analysis of only the significant points in the most informative areas. This ensures the establishment of the nature of the maximum number of quasibinary sections with a minimum number of syntheses. According to the results of phase analysis in combination with the literature data the triangulation of the Cu – Sn – Se system was carried out at 170 ° С. The quasibinarity of the Cu2Se – SnSe, Cu2Se – SnSe2, Cu2SnSe3 – Se, Cu2SnSe3 – SnSe, Cu6Sn5 – SnSe, Cu3Sn – SnSe, and Cu3Sn – Cu2Se sections was confirmed, and the quasibinarity of the Cu3Sn – Cu2Se was established at first. Keywords: triangulation; quasibinary section; phase analysis.

The study of physicochemical interaction was carried out by investigation of 12 samples within the Ag7PSe6 – AgSbP2Se6 system by DTA and XRD methods. The starting materials: Ag7PSe6 and AgSbP2Se6 were pre-synthesized from the elementary components of high purity. The thermal effects temperatures on the thermograms and X-ray diffraction data of compounds are in good agreement with the literature data. It was found that a cubic (SG P213) low-temperature modification of Ag7PSe6 and a trigonal (SG R3) modification of AgSbP2Se6, was obtained. A large number of effects appeared on the heating and cooling curves of the system samples, indicated that the physicochemical interaction in the Ag7PSe6 – AgSbP2Se6 system is complex. The thermograms show that the system consists of three distinct parts. X-ray diffraction results are in good agreement with DTA data. According to the results it is established: In the concentration range 100 – 44mol.% Ag7PSe6, up to the Ag4P2Se6–AgSbSe2–Se ternary system intersection the following reaction occurs: хAg7PSe6+(1-х)AgSbP2Se6=(7-7х)/5Ag4P2Se6+(1-х)AgSbSe2+(9х-4)/5Ag7PSe6+(2-2х)/5Se, where 0.44 ˂ x ˂ 1.00. 2. In the concentrations range 44 – 37.5 mol.% Ag7PSe6, from Ag4P2Se6–AgSbSe2–Se ternary system to Ag4P2Se6 –Sb2Se3 – Se ternary system intersections, the following reaction occurs: хAg7PSe6+(1-х) AgSbP2Se6=(2-х)/2Ag4P2Se6+(8х-3)AgSbSe2+(2-3.5х)Sb2Se3+2.5Se, where 0.375 ˂ x ˂ 0.44. In the concentrations range 37.5 – 0 mol.% Ag7PSe6, from the Ag4P2Se6 –Sb2Se3 – Se ternary system intersection with to AgSbP2Se6 the interaction is described by the equation: хAg7PSe6+(1-х)AgSbP2Se6=(3-8х)/3AgSbP2Se6+7х/4Ag4P2Se6+(1-х)/2Sb2Se3+(9-18х)/2Se, where 0˂ x ˂ 0.375. At the intersection points with the ternary systems the following chemical reactions take: 4Ag7PSe6 + 5AgSbP2Se6 = 7Ag4P2Se6 + 5AgSbSe2 + 2Se 6Ag7PSe6 + 10AgSbP2Se6 = 13Ag4P2Se6 + 5Sb2Se3 + 3Se. To clarify the nature of the interaction, 3 samples were additionally synthesized, with 30, 37.5, and 44.4 mol.% Ag7PSe6. The obtained samples were investigated by DTA, MSA and XRD. In the thermograms the absence of Ag7PSe6 polymorphic transformation effect and the presence of the selenium melting thermal effect were established. The study of the microstructure proved that all samples are multiphase. In the powder patterns of the sample with 30 mol.% Ag7PSe6 reflexes of Ag4P2Se6, AgSbP2Se6 and Sb2Se3 also. Diffractograms of samples with 37.5 and 44.4 mol% Ag7PSe6, which correspond to the intersection points of Ag7PSe6–AgSbP2Se6 with ternary systems Ag4P2Se6–Sb2Se3–Se and Ag4P2Se6–AgSbSe2–Se, were compared with the calculated for three-component mixtures in appropriate ratios. The calculated diffractograms are completely consistent with the experimental ones, which proves that the cross section Ag7PSe6–AgSbP2Se6 intersects Ag4P2Se6–Sb2Se3–Se and Ag4P2Se6–AgSbSe2–Se ternary, and Ag7PSe6–Ag4P2Se6–AgSbSe2–Se, Ag4P2Se6–AgSbSe2–Sb2Se3–Se, AgSbP2Se6–Ag4P2Se6–Sb2Se3–Se quaternary systems. Keywords: physic-chemical interaction; DTA; XRD; phase composition.

Cu1–xAgx)7GeSe5I-based ceramics were prepared by pressing and sintering from the micro- and nanopowders. The ceramic samples were investigated using microstructural analysis. The microhardness was measured applying the indentation method with use of the Vickers pyramid. It has been shown that the microhardness of (Cu1–xAgx)7GeSe5I-based ceramics decreases with copper content decrease at Cu+→Ag+cationic substitution. The compositional dependences and size effects of microhardness inherent to (Cu1–xAgx)7GeSe5I-based ceramics have been analyzed. The size effects of microindentation have been interpreted within the framework of the gradient theory of plasticity.

High-quality single crystals of Ag7(Si1–xGex)S5I (x = 0.2, 0.4, 0.6, 0.8) solid solutions are grown from the solution–melt by vertical zone crystallization method. The measurements of electrical conductivity of Ag7(Si1–xGex)S5I solid solutions were performed using the impedance spectroscopy method within the frequency range from 10 Hz up to 2·106 Hz and temperature interval 293–383 K. Ionic and electronic components of electrical conductivity, as well as their ratios, were determined using the Nyquist plots.

Searching for novel low-cost and eco-friendly materials for energy conversion is a good way to provide widespread utilization of thermoelectric technologies. Herein, we report the thermal behavior, phase equilibria data, and thermoelectric properties for the promising argyrodite-based Cu7P(SxSe1-x)6 thermoelectrics. Alloying of Cu7PSe6 with Cu7PS6 provides a continuous solid solution over the whole compositional range, as shown in the proposed phase diagram for the Cu7PS6-Cu7PSe6 system. As a member of liquid-like materials, the investigated Cu7P(SxSe1-x)6 solid solutions possess a dramatically low lattice thermal conductivity, as low as ∼0.2-0.3 W m-1 K-1, over the entire temperature range. Engineering the configurational entropy of the material by introducing more elements stabilizes the thermoelectrically beneficial high-symmetry γ-phase and promotes the multivalley electronic structure of the valence band. As a result, a remarkable improvement of the Seebeck coefficient and a reduction of electrical resistivity were observed for the investigated alloys. The combined effect of the extremely low lattice thermal conductivity and enhanced power factor leads to the significant enhancement of the thermoelectric figure of merit ZT up to ∼0.75 at 673 K for the Cu7P(SxSe1-x)6 (x = 0.5) sample with the highest configurational entropy, which is around twice higher compared with the pure selenide and almost four times higher than sulfide. This work not only demonstrates the large potential of Cu7P(SxSe1-x)6 materials for energy conversion but also promotes sulfide argyrodites as earth-abundant and environmentally friendly materials for energy conversion.

Ceramic samples based on the microcrystalline powders (Cu1–хAgx)7GeSe5I (x = 0, 0.25, 0.5, 0.75, 1) were prepared by pressing them at the pressure close to 400 MPa and subsequent annealing at 873 K for 36 hours. Using the microstructural analysis, the average size of microcrystallites of these samples was determined. Investigation of electrical conductivity of ceramics based on (Cu1 хAgx)7GeSe5I solid solutions was carried out using the method of impedance spectroscopy in the frequency range from 10 Hz to 3×105 Hz and within the temperature range 293...383 K. Analysis of the Nyquist plots allowed determining the contributions of ionic and electronic components to the total electrical conductivity. The temperature dependence of ionic and electronic conductivity in Arrhenius coordinates is linear, which indicates their thermoactivation character. The compositional behaviour of ionic and electronic conductivity, as well as their activation energies have been studied. Their nonlinear character can be explained by the complex process of recrystallization and Cu+ ↔ Ag+ cation substitution within the cationic sublattice.

In the frequency range of 6–106 Hz at a temperature of 293 K, the influence of (Cu6PS5I)0.5(Cu7PS6)0.5 superionic nanoparticles on electrical conductivity and dielectric properties of 6CB liquid cr...

The single crystals of quaternary halogen Ag6PS5I were grown from the solution–melt by means of a vertical zone crystallization method. The crystal structure has been ascertained using the Rietveld method. Investigation of electrical conductivity was carried out using the impedance spectroscopy technique within the frequency range 1·101 – 3·105 Hz and temperature interval 293–383 K on gold contacts applied by chemical deposition from solution. Ionic (1.79·10-3 S/cm) and electronic (1.64·10-6 S/cm) components of electrical conductivity have been determined using the Nyquist plots. The mechanism of ionic conductivity for Ag6PS5I single crystal has been proposed which can be considered as ion diffusion through “channels” Ag2–Ag2.

Cs- and Rb-containing halide double perovskites of A 2 B1B2X 6 type and vacant-ordered perovskites of A 2 B□X 6 type (where □ vacancy) are potential compounds for photovoltaic materials. Phase equilibria in the reciprocal Cs 3 Sb 2 Br 9 –Cs 2 TeI 6 « Cs 3 Sb 2 I 9 –Cs 2 TeBr 6 system were studied by methods of physicochemical analysis (DTA, X-ray, MSA) with the involvement of mathematical modeling. The Cs 3 Sb 2 Br 9 , Cs 3 Sb 2 I 9 , Cs 2 TeBr 6 , Cs 2 TeI 6 ternary compounds melts congruently at 864 K, 1019 K, 806 K, 876 K, respectively. The compound Cs 3 Sb 2 Br 9 has a polymorphic transformation at 791 K. Limited solid solutions are formed in the Cs 3 Sb 2 Br 9 –Cs 2 TeI 6 « Cs 3 Sb 2 I 9 –Cs 2 TeBr 6 system: a based on Cs 2 TeBr 6– х I х , b and b’ based on the low- and high-temperature modification of Cs 3 Sb 2 Br 9 , respectively, and g based on Cs 3 Sb 2 I 9 . Due to the formation an unlimited solid solution in the Cs 2 TeB 6 –Cs 2 TeI 6 system (can be considered as one component Cs 2 TeBr 6– х I х ) the investigated system may be presented as the Cs 3 Sb 2 Br 9 –Cs 3 Sb 2 I 9 –Cs 2 TeBr 6– х I х quasiternary system (characterized be eutectic invariant process L«a+b’+g at 737 K, 26 mol.% Cs 3 Sb 2 Br 9 , 32 mol.% Cs 3 Sb 2 I 9 , 19 mol.% Cs 2 TeB 6 , mol.% Cs 2 TeI 6 ). Consider the structure of octahedral [SbX 6 ] 3– complex ions within ligand field theory (LFT) and the molecular orbital (MO) method are detected. The structure of octahedral [SbX 6 ] 3– complex ions are characterized by sp 3 d 2 hybridization. Ab initio quantum-mechanical calculations of the electronic structure by DFT method were showed that all investigated compounds (except Cs 3 Sb 2 Br 9 ) belongs to indirect type semiconductors with band gaps E g = 2.24 eV (Cs 2 TeBr 6 ), E g = 1.43 eV (Cs 2 TeI 6 ), E g = 2.18 eV (direct type semiconductor Cs 3 Sb 2 Br 9 ), E g = 1.87 eV (Cs 3 Sb 2 I 9 ) and E g = 1.35 eV (Cs 2 TeBr 3 I 3 ). Optical studies of the fluorescence spectra of perovskite compounds of the Cs 3 Sb 2 X 9 type indicate the possibility of their use as promising functional photovoltaic materials for solar cell elements.

Thermoelectric technologies allow the direct conversion of waste heat into electricity. A new strategy for finding promising thermoelectric materials is to study the phase diagrams of multicomponent systems. Analysis of recent investigations indicates high perceptivity of Cu 2 Se phase, due to abnormally low values of the thermal conductivity and high values of electrical conductivity. Other thermoelectric materials based on copper have attractive properties, such as: diamond-like compounds, argyrodites, oxiselenides, tetrahedron-type compounds and others. Due to this a more detailed investiation of the Cu–Sb–Se system are actually. An important step in the study of the system is the determination of quasi-binary sections by carrying out the triangulation. For this purpose, the quasi-binarity of sections in the ternary Cu–Sb–Se system at a temperature of 523 K was determined by X-ray diffraction analysis. Since the annealing temperature in the synthesis process is 523 K, six binary Cu 2 Se, CuSe, CuSe 2 , Cu1 .6 Sb 0.4 , Cu 2 Sb, Sb 2 Se 3 and three ternary compounds CuSbSe 2 , Cu 3 SbSe 3 , Cu 3 SbSe 4 took part in the triangulation of the system. Analysis of the early studies showed the presence of three quasi-binary sections in the Cu–Sb–Se system: Cu 2 Se – Cu 3 SbSe 3 , Cu 3 SbSe 3 – CuSbSe 2 and CuSbSe 2 – Sb 2 Se 3 , and the character of the remaining 12 sections requires experimental studies. The quasi-binary section of Cu 2 Se-Sb 2 Se 3 divides the general system of Cu-Sb-Se into two subsystems: Cu 2 Se-Sb 2 Se 3 -Se (30 intersection points) and Cu-Sb-Sb 2 Se 3 -Cu 2 Se (13 intersection points). To optimize the process of triangulation, it was decided to carry out it in stages: synthesis and study of the point in the most informative phase field with following separation and exclusion of quasi-binary and non-quasi-binary sections. Such approach makes it possible to reduce the number of syntheses and the number of used substances. Phase analysis was performed by comparing experimental and calculated from the literature powder patterns of phases present in the systems Cu 2 Se-Sb 2 Se 3 -Se and Cu-Sb-Sb 2 Se 3 -Cu 2 Se. The obtained results indicate that in the subsystem Cu 2 Se-Sb 2 Se 3 -Se has seven stable sections, all of which are based on the ternary compound Cu 3 SbSe 4 . In the Cu-Sb-Sb 2 Se 3 -Cu 2 Se subsystem, 5 quasi-binary sections are stable: three based on binary Cu 2 Se and two sections based on ternary compounds CuSbSe 2 and Cu 3 SbSe 3 .

Copper-enriched (Cu0.75Ag0.25)7SiS5I-based ceramics were prepared from the micro- and nanopowders by pressing and sintering under developed technological conditions. Structural studies at different process step stages of ceramic samples preparation were performed using the XRD technique and microstructural analysis. The frequency and temperature dependences of the total electrical conductivity for (Cu0.75Ag0.25)7SiS5I-based ceramics were investigated by the impedance measurements. From the Nyquist plots, by using the electrode equivalent circuits the ionic and electronic components of the total electrical conductivity were determined. It has been shown that both ionic and electronic conductivity nonlinearly depend on the average crystallites size of (Cu0.75Ag0.25)7SiS5I-based ceramics.

The influence of Ag7GeS5I nanoparticles on dielectric properties of planar-oriented 6CB liquid crystal was investigated at 293 K within the frequency range from 6 to 106 Hz. The concentration of na...

Microhardness of (Cu1–xAgx)7GeSe5I mixed crystals and composites on their base was investigated using the Vickers indenter at room temperature. (Cu1–xAgx)7GeSe5I mixed crystals were obtained using the Bridgman–Stockbarger method. Composites on their base were prepared as a pressed mixture of (Cu1–xAgx)7GeSe5I micropowder and ethylene-vinyl acetate polymer in 90:10 concentration ratio, respectively. Dependences of microhardness versus the indenter penetration depth have been analyzed. Influence of Cu+→Ag+ isovalent cation substitution on the microhardness of (Cu1–xAgx)7GeSe5I mixed crystals and composites on their base have been studied.

Ceramic samples on the basis of nanocrystalline powders $\mathrm{c}_{\mathrm{u}1-\mathrm{x}} A \mathrm{g}_{\mathrm{x}})_{7}$GeSe5I(x=0,0.25,0.5,0.75,1) were made by cold pressing technique at a pressure of $\sim$0.4 GPa with further annealing during 36 hours at 873 K. The size of ceramic materials crystallites is determined by the method of microstructural analysis. Investigation of electrical properties of ceramics based on (Cu1-xA$\mathrm{g}_{\mathrm{x}})_{7}$GeSe5I mixed crystals were carried out by the method of impedance spectroscopy in the temperature range 293-383K and in the frequency range from 10 Hz to 300 kHz. Analysis of Nyquist plots allowed to determine the ionic and electronic components of electrical conductivity, the temperature dependence of which in Arrhenius coordinates has a linear character, which indicates their thermoactivation mechanism. Compositional behaviour of both components of electrical conductivity (ionic and electronic) and their activation energies were estimated. Their nonlinear character is explained by both the complex process of recrystallization and Cu+$\leftrightarrow$ Ag+ cationic substitution.

Галогенідні вакантно-впорядковані подвійні перовскіти типу A2B1B2X6 та типу A3B2X9 можуть бути використані в якості недорогих і високоефективних фотоелектричних перетворювачів сонячних елементів. Введення до структури тернарних сполук Диспрозію (Dy), повинно приводити до покращення оптичних, особливо люмінесцентних, властивостей. Згідно літературних даних у бінарній системі CsBr–SbBr3 утворюється сполука Cs3Sb2Br9 з конгруентним характером плавлення при 864 К, в системі CsBr–DyBr3 сполуки Cs3DyBr6 (плавиться конгруентно при 1086 K) та Cs3Dy2Br9 (інконгруентний характер плавлення 891 K).Для синтезу Cs3Sb2Br9 та (ТР) (Cs3Sb2Br9)1–х(DyBr3)х використовували стехіометричні кількості Sb, Br, Dy та додатково очищеного вакуумною переплавкою CsBr у спеціальних двохсекційних ампулах. Термічні дослідження показали, що між Cs3Sb2Br9 та DyBr3 утворюються граничні тверді розчини (до 3 мол.% DyBr3). Рентгеноструктурні дослідження показали, що сполука Cs3Sb2Br9 та ТР (Cs3Sb2Br9)0.97(DyBr3)0.03 кристалізуються у тригональній сингонії (P -3m1), параметри кристалічної гратки a=7.9061(5), c=9.7173(6) Å, V=526.02 Å3 та a=7.9150(6), с=9.7214(7) Å, V=527.43 Å3, відповідно. Твердий розчин утворюється внаслідок кратного заміщення атомів/йонів (3Cs+ + Sb3+) на атоми/йони 2Dy3+. Атоми Dy1, ймовірно, статистично розміщуються з атомами Cs2 у положеннях (1/3, 2/3, 0.6836), атоми Dy2 з атомами Sb у положеннях (1/3, 2/3, 0.1874). З позицій кристалохімічних формульних складів вивчено механізм утворення граничних твердих розчинів на основі сполуки Cs3Sb2Br9. У катіонній підгратці ТР (Cs3Sb2Br9)0.97(DyBr3)0.03 (кристалохімічний склад Cs294Sb197Dy5[.]4Br900) утворюються вакансії (4) за рахунок ізо- (3Dy®3Sb) та гетеровалентного (2Dy®6Cs) заміщення. В аніонній підгратці, яку формують іони Br–, їх кількість залишається сталою (900). Це вказує на формування твердого розчину за механізмом заміщення та віднімання (катіонна підгратка), заміщення (аніонна підгратка).Монокристали тернарної сполуки Cs3Sb2Br9 та твердого розчину (Cs3Sb2Br9)0.97(DyBr3)0.03 (діаметром 10 мм та довжиною 50 мм) вирощено методом Бріджмена. Вивчення залежності дифузійного відбиття від довжини хвилі R=f(λ) показало, що сполука Cs3Sb2Br9 та твердий розчин (Cs3Sb2Br9)0.97(DyBr3)0.03 відносяться до прямозонних напівпровідників, ширина забороненої зони Eg = 2.55 еВ (λ = 486 нм) та Eg = 2.59 еВ (λ = 479 нм), відповідно., Halogen vacant-ordered double perovskite type A2B1B2X6 and A3B2X9 compounds can be used as inexpensive and highly efficient photoelectric converters of solar cells. Introduction of Dysprosium (Dy) to the structure of ternary compounds should lead to improvement of optical, especially luminescent, properties. According to the literature data, the only compound Cs3Sb2Br9 (melts congruently at 864 K) is formed in the CsBr–SbBr3 binary system, while in the CsBr–DyBr3 system two compounds Cs3DyBr6 (melts congruently at 1086 K) and Cs3Dy2Br9 (melts incongruently at 891 K) are formed.The stoichiometric amounts of Sb, Br, Dy and additionally purified by vacuum melting of CsBr were used for syntheses of Cs3Sb2Br9 and solid solutions (Cs3Sb2Br9)1-x(DyBr3)x in special two-section ampoules. Thermal studies indicated the formation of boundary solid solutions between Cs3Sb2Br9 and DyBr3 (up to 3 mol.% DyBr3). According to X-ray diffraction studies compound Cs3Sb2Br9 and solid solution (Cs3Sb2Br9)0.97(DyBr3)0.03 crystallized in trigonal singony (P-3m1), lattice parameters are a=7.9061(5), c=9.7173(6) Å, V=526.02 Å3 and a=7.9150(6), с=9.7214(7) Å, V=527.43 Å3, respectively. The solid solution is formed by the multiple substitution of atoms / ions (3Cs+ + Sb3+) by atoms/ions 2Dy3+. Dy1 atoms are probably statistically located with Cs2 atoms in positions (1/3, 2/3, 0.6836), Dy2 atoms with Sb atoms in positions (1/3, 2/3, 0.1874). The formation mechanism of boundary solid solutions based on Cs3Sb2Br9 compound has been studied from the standpoint of crystal-chemical formulas. Vacancies (4) are formed in the cationic lattice of solid solutions (Cs3Sb2Br9)0.97(DyBr3)0.03 (crystallographic composition of (Cs294Sb197Dy5[ ]4Br900) due to iso- (3Dy®3Sb) and heterovalent (2Dy®6Cs) substitution. In the anionic lattice formed by Br– ions and their number remains constant (900). This indicates the formation of solid solution by the mechanism of substitution and subtraction (cationic sublattice), substitution (anionic sublattice).The single crystals of the ternary compound Cs3Sb2Br9 and solid solution (Cs3Sb2Br9)0.97(DyBr3)0.03 (diameter 10 mm and length 50 mm) were grown by the Bridgman method. The study of the dependence of the diffusion reflection on the wavelength R = f (λ) showed that the compound Cs3Sb2Br9 and solid solution (Cs3Sb2Br9)0.97(DyBr3)0.03 belong to direct-gap semiconductors, band-gap Eg = 2.55 eV (λ = 486 nm), Eg = 2.59 eV (λ = 479 nm), respectively.

Тернарні сполуки типу Tl4SnX3 (X–Se,Te) володіють низькою фононною теплопровідністю та високими значеннями ZT. Це обумовлює можливість їх використання у якості термоелектричних елементів. Для розширення області використання даних матеріалів актуальними є дослідження фізико-хімічної взаємодії у системах на основі фаз Tl4SnX3.Сполуки Tl4SnX3 утворюються у четверній системі Tl–Sn–Se–Te. Взаємодія сполук Tl4SnSe3 та Tl4SnТe3 здійснюється у межах потрійної взаємної системи Tl2Se+SnTe↔Tl2Te+SnSe. Бінарні фази Tl2Se, Tl2Te, SnSe та SnTe, які знаходяться в кутах концентраційного чотирикутника, плавляться конгруентно. Сполука SnSe зазнає поліморфне перетворення при 807K. Квазібінарні перерізи Tl2Se – Tl2Te та SnSe – SnTe відносяться до систем евтектичного типу. Системи Tl2Se–SnSe та Tl2Te–SnTe характеризуються утворенням тернарних сполук з конгруентним характером плавлення: Tl4SnSe3 (706K) та Tl4SnTe3 (817K); і фази Tl2Sn2Se3 (683K) з інконгруентним характером плавлення. Фаза Tl2Sn2Se3 існує лише у вузькому температурному інтервалі (640–683K). Кристалічна структура Tl2Sn2Se3 не відома. Тернарні Tl4SnSe3 і Tl4SnTe3 володіють широкими областями гомогенності. Існування тетрарної фази Tl2SnSeTe не підтверджено.Оскільки визначення квазібінарних перерізів проводиться нижче температурного інтервалу існування фази Tl2Sn2Se3, то вона не враховувалась при подальших дослідженнях. Таким чином, концентраційний чотирикутник системи Tl2Se+SnTe↔Tl2Te+SnSe характеризується наявністю 4 бінарних фаз (у вершинах) та двох тернарних фаз (на сторонах). Це обумовлює те, що система Tl2Sе+SnTe↔Tl2Te+SnSе може ділитися трьома квазібінарними перерізами на чотири квазіпотрійні системи. Всередині однієї з них реалізується один частково квазібінарний переріз на основі перитектичної фази Tl2Sn2Se3. Усі можливі перерізи перетинаються у 9 точках. Для визначення квазібінарних перерізів використовується експериментальний спосіб, який полягає у дослідженні фазового складу сплаву, що знаходиться на перетині можливих квазібінарних перерізів.Бінарні фази одержували сплавленням елементарних компонентів (чистота не менше 99.99 мас.%). Потрійні сполуки та сплави всередині системи Tl2Se+SnTe↔Tl2Te+SnSe здійснювали із попередньо синтезованих бінарних та тернарних халькогенідів у відповідних молярних співвідношеннях. Всі синтезовані сплави досліджували за допомогою аналізу ДТА, РФА і МСА.В результаті проведеного дослідження встановлено існування трьох квазіподвійних перерізів у потрійній взаємній системі Tl2Sе+SnTe↔Tl2Te+SnSе. Всі вони формуються на основі Tl4SnTе3 Квазіподвійний переріз Tl4SnSе3–Tl4SnTе3 поділяє загальну систему на дві вторинні: Tl2Se+Tl4SnTe3↔Tl2Te+Tl4SnSe3 та Tl4SnSe3+SnTe↔Tl4SnTe3+SnSe всередині яких реалізується стабільні перерізи Tl2Sе–Tl4SnTе3 та SnSе–Tl4SnTе3відповідно., The compounds of Tl4SnX3 (X – Se, Te) formula show low thermal conductivity and relatively high thermoelectric figure of merit ZT. Therefore compounds Tl4SnX3 can be used as perspective materials for thermoelectric devices. To increase the scope of use an investigation of the physico-chemical interaction in the systems based on the compounds Tl4SnX3 is promising.The Tl4SnX3 compounds are formed in the in quaternary Tl–Sn–Se–Te system and could be presented as ternary reciprocal system Tl2Se+SnTe↔Tl2Te+SnSe. The binary phases Tl2Se, Tl2Te, SnSe and SnTe, which are located in the corners of concentration quadrangle, melts congruently. The compound SnSe have a polymorphic transformation at 807 K. The Tl2Se–Tl2Te and SnSe–SnTe quasi binary sections refer to the eutectic type system. The quasi binary section Tl2Se–SnSe and Tl2Te–SnTe are characterized by the formation of several congruently melting ternary compounds: Tl4SnSe3 (706 K) and Tl4SnTe3 (817 K); and incongruently melting compound Tl2Sn2Se3 (683 K). The Tl2Sn2Se3 compound exists only in narrow temperature range (640–683 K), because of solid-state decomposing and its crystal structure is unknown. The ternary Tl4SnSe3 and Tl4SnTe3 have a wide homogeneity area. The existences of quaternary compound Tl2SnSeTe are not confirmed.Since the determinations of quasi binary sections are carried out below the temperature interval of the existence of the Tl2Sn2Se3 phase, it was not taken into account in further investigations. Thus, the concentration quadrangle of the Tl2Se+SnTe↔Tl2Te+SnSe system is characterized by the presence of 4 binary phases (at vertices) and two ternary phases (on the sides). This occurs that the Tl2Se+SnTe↔Tl2Te+SnSe system will be divided by three quasi binary sections on four quasi ternary systems. Inside one of them the partially quasi binary section, based on the incongruently melting phase Tl2Sn2Se3, will be realized. All possible sections intersect at 9 points.For determination of the quasi binary sections the experimental method was, which consists in investigation of the phase compositions of the alloy, which are at the intersection of possible quasi binary sections. The binary compounds were synthesized using high purity (99.99% mas.) elemental components. The ternary compounds and investigated alloys were obtained using the pre-synthesized binary compounds by one temperature method. All synthesized alloys were investigated by DTA, XRD and MSA analysis.Used the XRD method existence of three quasi binary sections Tl4SnSе3–Tl4SnTе3 Tl2Sе–Tl4SnTе3 and SnSе–Tl4SnTе3 were determined.

Використовуючи сучасні методи дослідження (диференційно-термічний ДТА, рентгенівський фазовий РФА аналізи та метод математичного моделювання) вивчено характер фізико-хімічної взаємодії в квазіпотрійній системі на основі складних телуридів талію(І) Tl4PbТe3–Tl9BiTe6–TlBiTe2, побудовано ізотермічний переріз при температурі 473 K, проекцію поверхні ліквідусу на концентраційний трикутник та просторову діаграму стану системи, встановлено детальний хід ліній моноваріантних рівноваг. Утворення нових складних сполук в системі Tl4PbТe3–Tl9BiTe6–TlBiTe2 не зафіксовано.Встановлення можливості модифікації складу вихідних тернарних сполук талію(І) Tl4PbTe3, Tl9BiTe6 та TlBiTe2 шляхом експериментального дослідження характеру фізико-хімічної взаємодії на їх основі є основною метою даної наукової роботи.Дана квазіпотрійна система утворена трьома квазіподвійними, дві з яких евтектичного типу Tl4PbТe3–TlBiTe2 (евтектика е2 відповідає 36 мол.% TlBiТe2, 756 K) та Tl9BiTe6–TlBiTe2 (евтектика е1 відповідає 52 мол.% Tl9BiTe6, 775 K), а також перерізом Tl4PbТe3–Tl9BiTe6, що характеризується утворенням неперервного ряду твердих розчинів без екстремальних точок на кривих ліквідуса і солідуса.Для дослідження фізико-хімічної взаємодії в системі Tl4PbТe3–Tl9BiTe6–TlBiTe2 було синтезовано ряд точок. Синтез бінарних, тернарних сполук та ряду сплавів здійснювався у вакуумних (0.13 Па) кварцових ампулах прямим однотемпературним методом. Максимальна температура синтезу на 50-70 K перевищувала температуру плавлення найбільш тугоплавкого компонента. Відпал проводили протягом 480 год при температурі 473 К. Охолодження до кімнатної температури - в режимі виключеної печі.На підставі результатів ДТА та РФА встановлено фізико-хімічну взаємодію в системі Tl4PbТe3–Tl9BiTe6–TlBiTe2 та побудовано ізотермічний переріз. За допомогою температур первинної кристалізації сплавів методом математичного моделювання вперше вивчено та побудовано проекцію поверхні ліквідусу системи Tl4PbТe3–Tl9BiTe6–TlBiTe2 на концентраційний трикутник. Встановлено, що поля первинних кристалізацій перетинаються вздовж лінії моноваріантної евтектичної рівноваги е1–е2. Даний моноваріантний евтектичний процес L«(Tl4PbTe3)х(Tl9BiTe6)1–х+(TlBiTe2) відбувається в інтервалі температур від 778 К (евтектика е1) до 763 К (евтектика е2). Характер фізико-хімічної взаємодії в квазіпотрійній системі Tl4PbТe3–Tl9BiTe6–TlBiTe2 добре описує побудована просторова діаграма стану., Using DTA, XRD and mathematical modelling methods the character of physicochemical interaction in the Tl4PbТe3–Tl9BiTe6–TlBiTe2 quasiternary system was studied, the isothermal section at the temperature of 473 K, projection of the liquidus surface and 3D state phase diagram was investigated. The detailed course of the lines of monovariant equilibria is established by the using of polynomial analysis. Formation of the new compounds in the Tl4PbТe3–Tl9BiTe6–TlBiTe2 system is not found.The main purpose of this scientific work was to establish the possibility of modifying the composition of the initial ternary compounds of thallium (I) Tl4PbTe3, Tl9BiTe6 та TlBiTe2, by experimentally studying of physico-chemical interaction on the basis of their.This quasiternary system is formed by three quasibinary sections, two of which belong to eutectic type Tl4PbТe3–TlBiTe2 (the eutectic е2 – 36 mol.% TlBiТe2, 756 К) and Tl9BiTe6–TlBiTe2 (the eutectic е1 – 52 mol.% Tl9BiTe6, 775 К), and the Tl4PbТe3–Tl9BiTe6 system, which is characterized by the formation of unlimited solid solutions without extreme points on the liquidus and solidus curves.To study the physico-chemical interaction in the Tl4PbТe3–Tl9BiTe6–TlBiTe2 system was synthesed a number of points. The synthesis of binary, ternary compounds and the number of alloys was carried out in evacuated (0.13 Pa) quartz ampoules using a direct one-temperature method. The maximum synthesis temperature on 50-70 K exceeds the melting point of the most initial component. Annealing was performed for 480 hours at a temperature of 473 K. Cooling to room temperature – in the mode of the off oven.On the basis of the obtained results it was established that the fields of primary crystallization intersect along the line of monovariant eutectic equilibrium e1-e2. This monovariant eutectic process L«(Tl4PbTe3)х(Tl9BiTe6)1–х+(TlBiTe2) takes place in the temperature range from 778 K (eutectic e1) to 763 K (eutectic e2). The character of the physico-chemical interaction in the quasiternary system Tl4PbТe3–Tl9BiTe6–TlBiTe2 describes well the plot space phase diagram.

The purpose of the study was to determine the interaction in the systems based on the compounds AgSbP 2 Se 6 and AgSbSe 2 (Sb 4 (P 2 Se 6 ) 3 ). To achieve the goal, 13 samples were synthesized in the AgSbP 2 Se 6 – AgSbSe 2 (Sb 4 (P 2 Se 6 ) 3 ) systems. Synthesis was carried out in evacuated up to 0.13 Pa quartz ampoules. The initial materials were pre-synthesized AgSbP 2 Se6, AgSbSe 2 and Sb 4 (P 2 Se 6 ) 3 . Their synthesis was carried out from high purity elementary components taken in a stoichiometric ratio. The maximum temperature of synthesis was 40-50 K above the melting point of components, including the products of interaction. Homogenizing annealing was conducting at the temperature 573 K for 120 hours. The identification was carried out by differential thermal analysis (DTA) and X-ray powder diffraction (XRD) (DRON 4.07, Cu Kα radiation). Synthesis of alloys was carried out in a similar way. The maximum temperature of the synthesis was 900 K. Annealing was carried out at 573 K for 240 hours. The obtained samples were investigated by DTA and XRD methods. The AgSbP 2 Se 6 – AgSbSe 2 system belongs to the eutectic type with boundary solid solutions based on the starting components. The solubility on the AgSbP 2 Se 6 side is about 5 mol.%, and on AgSbSe 2 – about 8 mol.%. The primary crystallization lines in the system intersect at the eutectic point with coordinates 724 K, ~ 33 mol.% AgSbSe 2 . The homogeneity region of AgSbSe 2 with increasing temperature is strongly expanding and at an eutectic temperature up to 30 mol.%, whereas this is not observed for AgSbP 2 Se 6 . The synthesized samples in AgSbP 2 Se 6 – Sb 4 (P 2 Se 6 ) 3 system were compact ingots with a rather dim metallic shine. The indexing of the X-ray powder diffractograms show that two phases AgSbP 2 Se 6 and Sb 4 (P 2 Se 6 ) 3 are exist in the system. On the thermograms of samples two endothermic effects were observed. The temperature of the low-temperature endothermic effect practically did not change in the whole concentration range (5 – 95 mol.%), which indicated the eutectic interaction. Invariant eutectic point is located on the side of Sb 4 (P 2 Se 6 ) 3 , its coordinates are 646 K, ~ 96 mol.% Sb 4 (P 2 Se 6 ) 3 . The solubility areas based on the initial components at annealing temperature do not exceed 5 mol%.

Complex chalcogenide compound are widely used as working elements for semiconductor optical technology, thermal generation, solar power. Special attention is paid to compounds of the M2P2Se6 type (M – Ag, Cu) which due to its layer crystal structure possess promising ferroelectric, thermoelectric and electro-optical properties. Heterovalent substitutions of cations 2М2+ ® 4M1+ in the composition of M2P2Se6 type compounds must leads to deformation of the crystal structure, changing in the value of the dipole moment and, accordingly, to change the electro-physical properties. The Tl2Se–In2Se3–“P2Se4” system characterized by the formation of intermediate complex compounds which melts congruently TlInSe2 (1023 К), Tl4P2Se6 (758 К), TlInP2Se6 (875 К) and TlIn5Se8 (melts incongruently L+In2Se3«TlIn5Se8 at 1029 К), In4(P2Se6)3 (formed by syntactic reaction at 880 К). Triangulation of the Tl2Se–In2Se3–“P2Se4” system was shown that then divided on secondary quasiternary systems, one of them is Tl2Se–TlInSe2–Tl4P2Se6. Phase equilibria in the Tl2Se – TlInSe2 – Tl4P2Se6 quasiternary system were studied using classical methods of physicochemical analysis DTA (chromel-alumel thermocouple, with an accuracy of ±5 K), XRD (DRON-3-13 diffractometer, Cu Ka radiation, Ni filter, Guinier Huber G670 diffractometer, CuKα1 radiation), MSA (metallographic microscope Lomo Metam R1) in combination with the simplex method of mathematical modeling of phase equilibria in multi-component systems. Crystal structure calculation was carried out with program WinCSD. Investigation of physical-chemical interaction allowed to constructed perspective view of phase state diagram and liquidus surface projection of the Tl2Se–TlInSe2–Tl4P2Se6 ternary system. In the ternary system formed the boundary solid solution: a- on the basis of Tl2Se, b- on the basis of TlInSe2, g-, d-, e- on the basis of ltm-, mtm- and htm-Tl4P2Se6 (ltm, mtm, htm – low, middle and high temperature modification, respectively). The liquidus of the ternary system consists of primary crystallization areas: Tl2Se-е1-Е1-е2-Tl2Se (a phase), TlInSe2-е3-U2-U1-E1-TlInSe2 (b phase), m1-U1-E1-e2-m1 (g phase), m2-U2-U1-m1-m2 (d phase) and Tl4P2Se6-e5-U2-m2-Tl4P2Se6 (ε phase). The Tl2Se–TlInSe2–Tl4P2Se6 quasiternary system is characterized by the processes: monovariant eutectic L«htmTl4P2Se6+TlInSe2 (e5-U2, 776-693 К), monovariant eutectic L«Tl2Se+TlInSe2 (e1-Е1, 614-539 К), monovariant eutectic L«Tl2Sе+ltmTl4P2Se6 (e2-Е1, 610-539 К); monovariant peritectic L+mtmTl4P2Se6«ltmTl4P2Se6 (m1-U1, 640-620 К); monovariant peritectic L+htmTl4P2Se6« mtmTl4P2Se6 (m2-U2, 747-693 К); monovariant peritectic L+mtmTl4P2Se6«TlInSe2 (U2-U1, 693-620 К); monovariant peritectic L+ltmTl4P2Se6«TlInSe2 (U1-E1, 620-539 К). Lines of the monovariant equilibria are crossed in three point: U2 – invariant peritectic process L+htmTl4P2Se6«TlInSe2+mtmTl4P2Se6 (12 mol.% Tl2Se, 20 mol.% TlInSe2, 68 mol.% Tl4P2Se6, 693 К), U1 – invariant peritectic process L+mtmTl4P2Se6«TlInSe2+ltmTl4P2Se6 (38 mol.% Tl2Se, 9 mol.% TlInSe2, 53 mol.% Tl4P2Se6, 620 К), E1 – invariant eutectic process L « Tl2Se+TlInSe2+ltmTl4P2Se6 (47 mol.% Tl2Se, 7 mol.% TlInSe2, 46 mol.% Tl4P2Se6, 539 К). New complex compounds were not observed in the ternary system. Limited solid solutions on the basis of TlInSe2, Tl4P2Se6 initial compounds are not up to 5–8 mol%. Crystal-structure studies of Tl2Se, TlInSe2 and Tl4P2Se6 complex chalcogenides were carried out by a powder method, refinement of the structural parameters – by the Rietveld method. The lattice parameters are: Tl2Se – Р4/n, а=8,540; с=12,380 Å, TlInSe2 – I4/mcm, a=8.064, c=6.833 Å, Tl4P2Se6 – P121/c1, a=12.239, b=9.055, c=12.328 Å, b=98.83. Crystal-chemical analysis of the compounds showed that they are characterized by a mixed ion-covalent type of chemical bond. During the transition from the binary Tl2Se to TlInSe2 ternary compound the covalent component of the In–Se bond is enhanced, the opposite change is observed for Tl4P2Se6, an increase in the ion component of the Tl–Se bond. The study of the mechanisms of formation of solid solutions showed that with the reciprocal solubility of the TlInSe2, Tl4P2Se6 ternary compounds characterized by the formation of substitution structure, the dissolution of Tl2Se in ternary selenides follows the substitution and subtraction mechanism.

The structure and optical properties of Bridgman-grown (Cu6PS5Br)1-x(Cu7PS6)x mixed crystals are reported. X-ray diffraction data reveal a face-centred cubic lattice ( F 4 ¯ 3 m space group) for Cu6PS5Br-rich crystals (0

(Cu0.25Ag0.75)7SiS5I-based superionic ceramics were fabricated by using the micro- and nanopowders. The XRD technique and microstructural analysis are applied for the structural studies of powders and ceramic samples. The impedance measurements of ceramic samples are carried out in the frequency range from 10Hz to 2 × 106 Hz and temperature interval from 292 K to 383 K. The contributions of ionic and electronic conductivities into the total electrical conductivity are determined, and their temperature dependences are investigated. The influence of the size effect on ionic and electronic conductivities and their activation energies in (Cu0.25Ag0.75)7SiS5I-based ceramics is studied., Отримано суперiоннi керамiчнi зразки на основi твердого розчину (Cu0.25Ag0.75)7SiS5I з використанням мiкро- та нанопорошкiв. Для структурних дослiджень порошкiв та керамiчних зразкiв використано методи РФА та мiкроструктурного аналiзу. Iмпеданснi вимiрювання керамiчних зразкiв проводилися в частотному дiапазонi вiд 10 до 2 · 106 Гц та температурному iнтервалi 292–383 K. Визначено внески iонної та електронної провiдностей у загальну електропровiднiсть, дослiджено їх температурнi залежностi. Вивчено вплив розмiрного ефекту на iонну та електронну провiднiсть та розраховано енергiї активацiї керамiчних зразкiв.

The system Ag(2-х)SbхP2хSe(1+5х) (0˂х˂1), based on Ag2Se and AgSbP2Se6 is realized in the quaternary system Ag – Sb – P – Se. Pre-synthesized Ag2Se and AgSbP2Se6 were the starting components for the synthesis of samples in the system. The initial components were synthesized from elementary components of high purity taken in stoichiometric ratios by the direct single-temperature method in evacuated up to 0.13 Pa quartz ampoules. The synthesis temperature was 40-50 K higher than the melting points of the components, including intermediates. The compounds were identified by differential thermal (DTA) and X-ray powder diffraction (XRD) analyzes. Two endothermic effects were observed on the thermogram of the Ag2Se compound: at 402 ± 5 K, which corresponds to the polymorphic transformation of Ag2Se, and at 1165 K, which corresponds to the melting of Ag2Se. One endothermic effect was observed on the AgSbP2Se6 thermogram at 740 ± 5 K. The DTA data for both compounds were in good agreement with the literature and confirmed the congruent nature of their melting. According to the X-ray diffraction results, it was established that we obtained a trigonal modification of AgSbP2Se6 and a low-temperature modification of Ag2Se. The obtained powder patterns were completely consistent with the powder patterns calculated according to the literature data. The synthesis of nine samples (x = from 0.05, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 0.9, 0.95) was carried out by a method similar to the synthesis of the starting compounds from previously synthesized Ag2Se and AgSbP2Se6. The maximum synthesis temperature was 1250 K, and exposure at this temperature was 72 hours. To the annealing temperature (573 K) cooling was carried out at a rate of 70 K/h. The duration of annealing was 240 hours. The obtained samples were investigated by DTA and XRD methods (DRON 4.07, Cu Kα radiation). Thermograms of samples of the Ag(2-х)SbхP2хSe(1+5х) (0˂х˂1) system was characterized by a significant number of thermal effects, which is evidence of a complex physicochemical interaction in the studied system. The X-ray diffraction results showed that the powder patterns of the samples are characterized by the presence of reflexes that do not belong to the original components. To clarify the nature of the interaction in the system Ag(2-х)SbхP2хSe(1+5х), samples with x = 0.11 and x = 0.33 were additionally synthesized. By comparing the experimental powder patterns with the calculated for the compounds realized in the quaternary Ag – Sb – P – Se system by literature data and for the corresponding phase mixtures, the phase composition was established and the mechanism of interaction during synthesis with Ag2Se and AgSbP2Se6 in the Ag(2-х)SbхP2хSe(1+5х) (0˂х˂1) system was proposed. According to the obtained data in the system Ag(2-х)SbхP2хSe(1+5х) (0˂х˂1) five phase regions are realized: one two-phase (Ag4P2Se6 and AgSbSe2, at x = 0.33), two three-phase (Ag, Ag7PSe6 and AgSbSe2, at x = 0.11 and Ag4P2Se6, AgSbSe2 and AgSbP2Se6, at 0.33˂x˂1), two four-phase (Ag, Ag2Se, Ag7PSe6 and AgSbSe2, at 0˂x˂0.11 and Ag, Ag7PSe6, Ag4P2Se6 and AgSbSe2, at 0.11˂х˂0.33).

The results of microhardness studies of $\mathbf{Ag}_{6+\mathbf{x}}(\mathbf{P}_{1-\mathrm{x}}\mathbf{Ge}_{\mathbf{x}})\mathbf{S}_{5}\mathbf{I}$ single crystals are presented. Established that with increasing the depth of the imprint of the Vickers indenter, a direct indentation size effect (ISE) is observed. Approximation and interpretation of the obtained results within the gradient theory of plasticity are carried out. The parameters of the geometrically necessary dislocations (GNDs) model are determined.

This work investigates band structure, total and partial densities of states, and full complex of optical functions of Ag 7 GeS 5 I crystal belongs to the family of compounds with an argyrodite structure using the density functional theory (DFT) improved by an on-site Coulomb self-interaction potential $(\mathbf{DFT}+\boldsymbol{U})$ . The lowest energy electronic transition occurs at the center of the Brillouin zone. The band gap energy is estimated in the DFT-LDA+U approximation, which is $E_{\mathbf{gd}}=1.68\mathbf{eV}$ ·

Ceramic samples based on $(c_{u1-x}Ag_{x})_{7}SiS_{5}I$ nanocrystalline powders were manufactured by pressing them at $\sim 400$ MPa pressure and subsequent annealing at 973 K during 36 hours. Investigations of electrical conductivity of ceramics based on $(c_{u1-x}Ag_{x})_{7}SiS_{5}I$ solid solutions were carried out by the method of impedance spectroscopy in the frequency range from 10 Hz to $2\times 10^{6}$ Hz and in the temperature range 292-383 K. It is established that with increasing the content of silver atoms in ceramic samples based on $(c_{u1-x}Ag_{x})_{7}SiS_{5}I$, the ionic component of electrical conductivity increases nonlinearly, while electronic component decreases nonlinearly, and their ratio increases nonlinearly and for $Ag_{7}SiS_{5}I$ exceeds 60000.

(CuxAg1−x)7SiS5I mixed crystals were grown by the Bridgman–Stockbarger method. The microhardness measurements are carried out at room temperature using a Vickers indenter. The compositional dependence of the microhardness is studied. The dependence of the microhardness on the depth of imprint is analyzed in the model of geometrically necessary dislocations. The indentation size effect is observed. It is established that the microhardness of (CuxAg1−x)7SiS5I mixed crystals decreases at the substitution of Cu atoms by Ag atoms., Кристали твердих розчинiв (CuxAg1−x)7SiS5I вирощували методами Брiджмена–Стокбаргера. Вимiрювання мiкротвердостi проводили при кiмнатнiй температурi за допомогою iндентора Вiккерса. Дослiджено композицiйну залежнiсть мiкротвердостi кристалiв (CuxAg1−x)7SiS5I у залежностi вiд глибини занурення iндентора Вiккерса. Залежностi мiкротвердостi вiд глибини вiдбитка були проаналiзованi в рамках моделi градiєнта пластичної деформацiї. Виявлено розмiрнi ефекти при мiкроiндентуваннi кристалiв (CuxAg1−x)7SiS5I. Встановлено, що при замiщеннi атомiв Cu атомами Ag проходить зниження мiкротвердостi кристалiв (CuxAg1−x)7SiS5I.

Single crystals of (Cu1-хAgx)7GeS5I solid solutions were grown by vertical zone crystallization method. XRD studies have shown that they crystallize in face-centered cubic lattice of the argyrodite structure (space group F 4 ¯ 3 m , Z = 4). Structural studies were performed on the basis of original structure model by means of Rietveld refinement method. Electrical measurements were carried out in the temperature interval 300–360 K and in the range of frequencies 10 Hz–10 GHz. Temperature and frequency dependences of electrical conductivity were analyzed. Influence of cation substitution on the electrical conductivity as well as relationship between structural and electrical properties of (Cu1-хAgx)7GeS5I solid solutions were studied.

Polymer composites based on (Cu1−xAgx)7GeSe5I solid solutions are produced. The electrical conductivity of the composites is measured by impedance spectroscopy in the frequency range from 20 Hz to 2×106 Hz and in the temperature interval 292–338 K. The frequency dependences of the total electrical conductivity are obtained, the Nyquist plots are constructed, and their analysis is performed. The effect of Cu+ →Ag+ cationic substitution on the total electrical conductivity and the activation energy, as well as on the electronic and ionic components of the electrical conductivity of composites based on (Cu1−xAgx)7GeSe5I solid solutions is studied on the basis of compositional dependences., Виготовленi полiмернi композити на основi твердих розчинiв (Cu1−xAgx)7GeSe5I. Вимiряно їх провiднiсть методом iмпедансної спектроскопiї на частотах вiд 20 до 2·106 Гц при температурах 292–338 K. Отримано частотну залежнiсть загальної провiдностi, побудованi графiки Найквiста i дано їх аналiз. З урахуванням залежностi вiд композицiї вивчено дiю замiни Cu+ →Ag+ на загальну провiднiсть, енергiю активацiї i на електронну та iонну компоненти провiдностi композитiв на основi твердих розчинiв (Cu1−xAgx)7GeSe5I.