Enhancing the chemical vapor deposition with the aid of plasma (PECVD) supposes the formation of ions, radicals, and neutrals for film deposition and etching surfaces. The low operating temperatures of PECVD allows hydrogenation of amorphous solids to max out their semiconductor properties. In this work, X-ray amorphous PECVD Si-C-N-H films derived from the mixture of hexamethyldisilazane (HMDS), hydrogen, and argon were investigated. We explored the impact of the hydrogen flow rate (FH) supplied to the vacuum chamber separately and gases used in the HMDS delivery system on the photoluminescence (PL), chemical bond, structure, and morphology of the films. FH strongly affects the etching rate during deposition, altering the film thickness, size of grain-like agglomerations, concentrations of Si-C, Si-N, C-H bonds and defects, and consequently, affects the PL spectra. Replacing hydrogen with argon in the HMDS delivery system leads to a controversial trend in the dependencies of film properties on the FH. The low temperature (LT) PL has a narrow band at 419-428 nm that is quenched at room temperatures (RT). In contrast, an asymmetrical wide band with partial maxima at 435-458, 473-496, 520-551, 566-623, and 650-680 nm appears in both LT and RT PL. Possible mechanisms of the photoemission are suggested.

The films of the Ti-Nb-C system were deposited by direct current (DC) magnetron co-sputtering of composite Ti+Nb, and graphite targets onto Si substrates to which negative substrate bias in the range of -50÷-200 V was applied during film deposition. The microstructure, chemical bonds, and mechanical properties of films were comparatively investigated. The X-ray diffraction (XRD) analysis revealed that the peaks of the XRD spectra of the film obtained by co-spattering of the composite Ti+Nb and graphite targets are located in the intermediate region between the corresponding peaks of the Ti-C and Nb-C films. The X-ray photoelectron spectroscopy (XPS) showed that the Ti-C and Nb-C bonds prevail in the deposited Ti-Nb-C films. It was suggested that the Ti-Nb-C films are nanocomposite and consist of the crystallites of Ti1-xNbxCy solid solutions surrounded by amorphous carbon-based matrix. The Knoop hardness of the Ti-Nb-C film is highest (37.5 GPa) in the film deposited at -50 V substrate bias. The average friction coefficient determined before film delamination was the lowest (0.12) in that Ti-Nb-C film.

The (TiZrHfNbTa)B2 2 films were prepared by direct current magnetron sputtering of the target manufactured of TiB2, 2 , ZrB2, 2 , HfB2, 2 , NbB2, 2 , and TaB2 2 powders at different substrate biases (0,-50,-100,-150,-200 V). The structure, surface morphology, chemical bonding, Knoop hardness, and tribological properties were studied by Xray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic-force microscopy, Raman spectroscopy, Rutherford backscattering, indentation and tribological tests. The crystalline phase was observed in the film's structure. The XPS results point to the formation of the following bonds in films: Ti-B, Ti-B-O, Zr-B, Nb-B, Hf-B, Hf-O, Ta-B. The XRD and XPS results allowed the conclusion on formation of a solid solution of constituting diborides. The film hardness increased from 34.8 GPa (Ub b = 0 V) to maximum value of 38.3 GPa (Ub b =-150 V) and then decreased to 33.2 GPa (Ub= b =-200 V). The friction coefficient mu decreased with increasing substrate bias from 0.85 to 0.49 exhibiting the minimal value for the film with the smallest hardness. A comparative first-principles investigation of the stability, electronic structures and mechanical properties of the random high entropy diborides (TiZrHfMTa)B2 2 (M=Nb, Sc, V, Mo) and the constituting binary diborides was performed to interpret the properties of deposited films. The calculated elastic moduli, Vickers hardness, fracture toughness, and Debye temperature of (TiZrHfMTa)B2 2 alloys are close to the average values of the corresponding characteristics of constituting diborides. First-principles calculations show that the formation of quinary high entropy diborides, in which TiB2 2 is a constituent compound does not lead to an improvement in their mechanical characteristics compared to those of TiB2. 2 .

This study investigates the phase composition, microstructure, and their influence on the properties of Mo-W-C nanocomposite films deposited by dual-source magnetron sputtering. The synthesised films consist of metal carbide nanograins embedded in an amorphous carbon matrix. It has been found that nanograins are composed of the hexagonal β-(Mo2 + W2)C phase at a low carbon source power. An increase in the power results in the change in the structure of the carbide nanoparticles from a single-phase to a mixture of the β-(Mo2 + W2)C and NaCl-type α-(Mo + W)C(0.65≤k≤1) solid-solution phases. The analysis of electrical properties demonstrates that the nanograin structure of the films favours the occurrence of hopping conductivity. The double-phase structure leads to a twofold increase in the relaxation time compared to the single-phase one. Films with both types of nanograin structures exhibit tunnelling conductance without the need for thermal activation. The average distance between the potential wells produced by the carbide nanograins in nanocomposite films is approximately 3.4 ± 0.2 nm. A study of tribomechanical properties showed that Mo-W-C films composed of a mixture of the β-(Mo2 + W2)C and α-(Mo + W)C(0.65≤k≤1) phases have the highest hardness (19–22 GPa) and the lowest friction coefficient (0.15–0.24) and wear volume (0.00302–0.00381 mm2). Such a combination of electrical and tribomechanical properties demonstrates the suitability of Mo-W-C nanocomposite films for various micromechanical devices and power electronics.

First-principles investigations of the stability, mechanical properties, electronic and phonon structures, as well as molecular dynamics simulations of temperature- and pressure-induced phase transitions in boron carbonitrides, BC1-xNx, for x = 1.0 (C0), 0.75 (C1), 0.5 (C2), 0.25 (C3) and 0.0 (C4), were carried out. The plausible mechanisms of the phase transitions in BNs were proposed and the transformation paths were established for the h -> w, r -> c, c -> r and w -> h' transitions, where h' was the new hP4-187 phase (space group P-6m2, #187). The non-layered C0-C3 compounds transformed into the layered ones at 2000-3000 K. The new BC1-xNx structures are brittle materials and exhibit the best combination of hardness (23.1-60.8 GPa) and fracture toughness (4.03-5.23 MPa m1/2). The C1-C4 structures are metallic, except for three compounds: C1-oP8-25 and C4-tP8-136 are semimetals, and C4-mP8-10 is a semiconductor with a very narrow bandgap of 0.2 eV.

TiZrMoC coatings were deposited on Si(100) substrates using a DC dual magnetron sputtering. The composition was controlled by adjusting the sputtering parameters of the TiZrMo and graphite targets. The influence of graphite target current on the resulting coating properties was explored. TEM analysis revealed a single-phase structure with Ti/Mo/Zr substitutional elements, columnar grains, and a strong [111] texture. Nanotwins and stacking faults were prevalent within the nanocrystals. EDX, SIMS, XRD, and XPS analyses confirmed the elemental composition and nanostructure. Computational modeling was employed to investigate the mixing behavior of the quaternary solid solutions depending on the valency electron concentration. The films exhibited exceptional mechanical properties, including a maximum hardness of 35 GPa and a wear rate of 2.11 × 10−7 mm3N−1m−1, attributed to the presence of an amorphous carbon layer and optimized deposition parameters. These findings demonstrate the potential of TiZrMoC coatings for advanced applications requiring exceptional wear resistance and durability.

One of the fundamental goals of materials science is to understand and predict the formation of complex phases. In this study, FeSi2 is considered as an illustration of complex phase formation. Although Fe and Si both crystallize with a simple structure, namely, body-centered cubic (bcc A2) and diamond (A4) structures, respectively, it is rather intriguing to note the existence of two complex structures in the Si-rich part of the phase diagram around FeSi2: α-FeSi2 at high temperatures (HT) with a slight iron-deficient structure and β-FeSi2 (also referred to as Fe3Si7) at low temperatures (LT). We re-analyze the geometry of these two phases and rely on approximant phases that make the relationship between these two phases simple. To complete the analysis, we also introduce a surrogate of the C16 phase that is observed in FeGe2. We clearly identify the relationship that exists between these three approximant phases, corroborated by a ground-state analysis of the Ising model for describing ordering that takes place between the transition metal element and the “vacancies”. This work is further supported by ab initio electronic structure calculations based on density functional theory in order to investigate properties and transformation paths. Finally, extension to other alloys, including an entire class of alloys, is discussed.

Nanolayered Tі–B/C films are deposited by sequential DC magnetron sputtering of TіB2 and graphite targets. The Si(100) platelets preliminarily heated to 400°C are used as substrates to which negative bias voltage of 50 V is applied. The operating parameters remain unchanged for the TіB2 target, whereas the sputtering current is varied within 50–200 mA for the graphite target. The structure, chemical bonding, Knoop hardness, and friction coefficient as functions of the sputtering current (Is) at the graphite target are studied by the methods of XRD, XPS, indentation, and tribological testing. The crystalline phase is detected in the films structure, which differs from that for TіB2. The film deposited at Іs = 150 mA exhibits the maximum hardness, and the film deposited at Іs = 200 mA has the minimum friction coefficient.

The review presents the results of theoretical and experimental studies of the structure, bonding between atoms, mechanical properties, thermal stability, and oxidation and corrosion resistance of films based on ternary tran-sition metal borides.

First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (& epsilon; phase) to WC-type TaN (& theta; phase) and & epsilon; to NaCl type-TaN (& delta; phase) structural transformations that were observed in experiments and for the & theta; to hP4-194, & theta; to cP2-221, & delta; to cP2-221 and & delta; to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the & theta; phase (by 0.014-0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1-34.2 GPa), fracture toughness (5.52-5.59 MPa m1/2) and Debye temperatures (609.7-616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper.

The high-precision analytical study of sphalerites from Pitkäranta ore deposits used microprobe and La-ICP-MS analyses. Average concentrations of minor (Fe, Cu, Mn, Cd) and trace elements (In, Сo, Ni, Ga, Ge, As, Ag, Sn, Sb, Te, Au, Tl, Pb, Bi) in sphalerite were calculated from 169 analyses. It is shown that most analyzed elements are present in sphalerite as isomorphic components. The average content of In in sphalerite is 1927 ppm, and its maximum content is 1.5 wt

The paper reports the results of studies on critical metal mineralization genetically related to the late-stage intrusions of Salmi anorthosite-rapakivi granite batholith (SARGB) in the Riphean age. In, Bi, and Be mineralization in skarn-greisen deposits and occurrences at the SARGB endocontact, as well as REE and Nb-Ta mineralization in Li-F granites, understood as the late intrusive phases of the batholith, were studied. It is the first report on columbite-group minerals, as well as REE-Ta-Nb and REE mineralization in SARGB granites. Optical and scanning electron microscopy, EDS and LA ICP MS microanalysis, X-ray fluorescence spectrometry, Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS) were used. The data obtained show that roquesite formation was mainly triggered by the decay of In-bearing solid sphalerite and chalcopyrite solutions. Zavaritskite, associated with unoxidized sulphides, was derived hypogenically and seldom occurs in ores. A helvine-group mineral association with zinc-enriched spinel (ZnO 22%–25%) seems to have been one of the factors preventing genthelvite formation. The Muzilampi, Hepaoja and Avtodor ore occurrences in Li-F granites display similar REE and Nb-Ta mineralization. They are associated with Y-fluorite and Li-siderophyllite, which contain exceptionally high Nb concentrations (0.25%–0.78%) in Muzilampi granites. Additionally, fluorite-1 is commonly overfilled (to >50%) with micron-sized synchisite and parisite inclusions. Columbite-tantalite-group minerals, present at all the occurrences studied, occur solely as ferricolumbites with a dominant Mn/(Mn + Fe) ratio of <0.2. Biotite and Li-siderophyllite, associated with columbite, have an extremely high iron index Fe/(Fe + Mg) > 0.9 approaching the maximum values (~1.0) in the most differentiated granites.

Structural transformations at high temperatures and pressures, elastic moduli, hardness, fracture toughness, Debye temperature, stress-shear strain relations, electronic structure, and lattice dynamics in the experimentaly observed NaCl–NbN (δ, Fm-3m), anti-TiP-NbN (ε, P63/mmc), anti-NiAs-NbN (δ′, P63/mmc), WC-NbN (η, P-6m2), and TiP–NbN (ε′, P63/mmc) phases and hypothetical new tP4-129 (P4/nmm), hP6-189 (P-62m), oP8-25 (Pmm2) and cP2-221 (Pm-3m) structures are studied by using first-principles calculations and molecular dynamics simulations. The possible mechanisms of the phase transitions between these structures based on the condensation of a certain phonon mode with subsequent spontaneous strains are suggested. The ε, η and δ′, and cP2-221 structures are brittle materials and exhibit highest shear moduli (200.5–216.8 GPa), Young moduli (492.4–528.8 GPa), Vickers hardness (23.9–27.1 GPa), fracture toughness (4.54–4.72 MPa m1/2), and Debye temperatures (730.5–767.0 K). It is found that the main slip systems should be (0001)<10-10> for ε and η, and both (0001)<10-10> and (0001)<-12-10> for δ’.

First-principles calculations and molecular dynamics (FPMD) simulations in the constant number of particles - pressure - temperature (NPT) ensemble were used to investigate the phase stability, phase diagram, electronic and phonon structures, chemical bonding, mechanical, thermodynamical and optical properties of various tungsten carbide polytypes as well as the hexagonal (alpha) and cubic (beta) Ti1-xWxCy solid solutions. The known alpha-WC (P-6m2) and beta-WCy (Fm-3m) polytypes and eight hypothetical ones were studied. Gibbs free energy calculations predicted the alpha-WC -> beta-WCy and alpha-WC -> tP4-129 (P4/nmm) phase transitions. The P-6m2 -> Fm-3m -> I41md, Fm-3m -> P4/nmm and P-6m2 -> Pm-3m phase transformations were revealed during FPMD simulations of: alpha-WC at T = 2500 K, beta-WC at T = 100 K, and alpha-WC at T = 2500 K and P = 500 GPa, respectively. It is found that the known alpha-polytype and new tI8-109 (I41md), oP12-25 (Pmm2), hP4-194 (P63/mmc), hP8-194 (P63/mmc), cP2-221 polytypes are ultraincompressible and ultrastiff materials, and exhibit the highest hardness (29-38 GPa), fracture toughness (4.7-7.2 MPa m1/2) and Debye temperature (615-663 GPa). Other characteristics of the WC polytypes, namely, the stress-shear strain curves, dielectric function, reflectivity spectra, heat capacity and spatial distribution of the elastic moduli, were calculated and discussed. The stability, mechanical properties and lattice parameter of beta-WCy and Ti1-xWxCy as functions of composition were studied. The binodal and spinodal for Ti1-xWxC were calculated. The calculated characteristics are compared with available experimental data and used for their interpretation.

Nanocomposite multilayer coatings are of large interest to the engineering industry because of their functional properties. Titanium nitride-based multilayer structures are very effective as protective layers for mechanical instrumentation. In this paper, selected mechanical and tribological properties for cutting machinery of TiASiYN/CrN system were considered. The columnar (111) coherent growth of the TiAlSiYN on the CrN without layers mixing has been identified via TEM and XRD. But crystal orientation, crystallite size and residual strain were varied depending on Cr interlayer and pre-treatment. Analysis of the experimental data manifests a decomposed Ti0.25Al0.75N phase stabilized by CrN that was suggested as one of the main factors responsible for superhard phase formation. Wear and scratch experiments highlighted improved wear, crack resistance and adhesion to the substrate (Lc5 = 150.1 N) in the sample prepared in Cr plasma without Cr interlayer. Cutting analysis proved the exceptional durability of inserts after coating deposition. Fracture mechanisms were found out to carry an adhesive character over the cohesive.

A short review of studies on the structure, stability and properties of the transition metal carbides and nitrides/(SiC, SiN, AIN, BN) heterostructures that model corresponding nanocomposite and nanolayered coatings was done. For the first time, the stability of the BN, BC, AIN and SiC interfaces in the transition metal diborides-based heterostructures were analyzed using first-principles molecular dynamics simulations. It was shown that the initial hetero-epitaxial BN, AIN and SiC interfaces with the graphene-like structure in the heterostructures were dynamically unstable due to the large mismatch in the lattice parameters of the diborides and non-metal interfacial materials. As a result, the amorphous interfacial BN layer and distorted rock-salt-like AIN and SiC interfaces formed after relaxation or molecular dynamics simulations. The BC interface was found to have a hetero-epitaxial structure up to 1400 K. The suggested criterion of interface stability enabled one to predict temperature-induced structural transformations of the non-metal interfacial layers in 3d, 4d, and 5d transition metal diboride-based heterostructures.

First-principles calculations were carried out to study the hypothetical MoC, Mo2C, Mo3C2 and random MoCx, x = 1.0, 0.875, 0.75 and 0.5 phases, and those that were experimentally verified, as well as the random cubic and hexagonal TiC-MoC and cubic and orthorhombic Ti2C-Mo2C solid solutions (alloys). The electronic and phonon structures, formation energy, elastic constants and moduli, hardness, Debye temperature, fracture toughness and stress-strain relation for these structures were calculated in order to understand the differences in phase stability; to explain their properties; and to predict possible new stable phases. The phase diagrams of the Mo-C system for three compositions, 67 at.% Mo + 33 at.% C, 60 at.% Mo + 40 at.% C and 50 at.% Mo + 50 at.% C, were built in the temperature range of 0-4000 K. First-principles molecular dynamics simulations and the group-theoretical analysis are used to identify the plausible mechanisms of the temperature-induced structural transformations in the alpha-, gamma- and gamma'-phases of MoC. The composition dependence of the mechanical characteristics of the solid solutions was found to have an extremal character, and in particular a maximum hardness for the cubic Ti0.75Mo0.25C (27.2 GPa) and orthorhombic Ti0.5Mo1.5C (14.6 GPa) alloys. The theoretical phase stability diagrams for the Mo-C system and Ti-Mo-C alloys contain not only the structures experimentally observed but also hypothetical phases, and the available experimental properties were reproduced and explained.

Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10−6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.

Both first-principles study of the random TiC-NbC solid solutions and experimental investigation of the films in Ti-Nb-C system were carried out. The mixing energy, electronic and phonon structures, elastic constants and moduli, hardness, Debye temperature, fracture toughness, dielectric function, electron energy-loss spectra and heat capacity of the random Ti1-xNbxC solid solutions were calculated and analyzed depending on composition. The Ti-C, Nb-C and Ti-Nb-C films were deposited by magnetron sputtering. The deposited films were comprehensively studied with XRD, XPS, AFM, EDS, Raman spectroscopy, indentation and tribological tests. The Ti-Nb-C films with equi-atomic composition are found to exhibit the highest Knoop hardness and lowest friction coefficient as compared to those of the parent TiC and NbC carbides. The results obtained were used to establish the mechanism of the stabilization of the TiC-NbC solid solutions, and to predict their structural, mechanical, optical and thermodynamic properties.