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The temperature-dependent composition and phase formation during the physical vapor deposition (PVD) of Mg-Ca thin films is modeled using a CALPHAD-based approach. Considering the Mg and Ca sublimation fluxes calculated based on the vapor pressure obtained by employing thermochemical equilibrium calculations, the experimentally observed synthesis-temperature trends in the thin-film composition and phase formation were reproduced. The model is a significant step towards understanding how synthesis parameters control composition and, therefore, phase formation in the PVD of metals with high vapor pressures. [ABSTRACT FROM AUTHOR]

Though the positive role of alkali halides in realizing large area growth of transition metal dichalcogenide layers has been validated, the film-growth kinematics has not yet been fully established. This work presents a systematic analysis of the MoS2 morphology for films grown under various pre-treatment conditions of the substrate with sodium chloride (NaCl). At an optimum NaCl concentration, the domain size of the monolayer increased by almost two orders of magnitude compared to alkali-free growth of MoS2. The results show an inverse relationship between fractal dimension and areal coverage of the substrate with monolayers and multi-layers, respectively. Using the Fact-Sage software, the role of NaCl in determining the partial pressures of Mo- and S-based compounds in gaseous phase at the growth temperature is elucidated. The presence of alkali salts is shown to affect the domain size and film morphology by affecting the Mo and S partial pressures. Compared to alkali-free synthesis under the same growth conditions, MoS2 film growth assisted by NaCl results in ≈81% of the substrate covered by monolayers. Under ideal growth conditions, at an optimum NaCl concentration, nucleation was suppressed, and domains enlarged, resulting in large area growth of MoS2 monolayers. No evidence of alkali or halogen atoms were found in the composition analysis of the films. On the basis of Raman spectroscopy and photoluminescence measurements, the MoS2 films were found to be of good crystalline quality. [ABSTRACT FROM AUTHOR]

The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous Fe 1 - x Zr x alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials. [ABSTRACT FROM AUTHOR]

The phase formation of Nb 2 AlC was studied by combinatorial thin film synthesis and ab initio calculations. Thin films with lateral chemical composition gradients were synthesized by DC magnetron sputtering at substrate temperatures of 710–870 °C. The lowest formation temperature for Nb 2 AlC is between 710 and 750 °C. A predominantly single phase Nb 2 AlC region where 99% of the X-ray diffraction intensity originate from Nb 2 AlC was identified. Furthermore, selected area electron diffraction analysis reveals the local formation of single phase Nb 2 AlC. The limited Al solubility in Nb 2 AlC compared with Cr 2 AlC can be understood by comparing the defect formation energy of Al substituting Nb and Cr in Nb 2 AlC and Cr 2 AlC, respectively. This methodology may serve as indicator for the magnitude of the A-element homogeneity range in M n +1 AX n phases. The structural and elastic properties of Nb 2 AlC determined experimentally are in very good agreement with the ab initio calculated data. [ABSTRACT FROM AUTHOR]

Reactive cathodic arc evaporation of Ti-Al-O-N was carried out in an industrial deposition system with two-fold substrate rotation. The structural and compositional evolution of the coatings was studied by combining scanning transmission electron microscopy and 3D atom probe tomography (APT). The formation of alternating O- and N-rich sublayers was identified by APT and can be understood by considering the substrate rotation-induced variation in plasma density and fluxes of film-forming species. The effect of plasma density and fluxes on the incorporation of reactive species was studied in stationary deposition experiments and preferred N incorporation occurs, when the growing coating surface is facing the arc source. Thus, the growing surface is positioned in a region of high plasma density characterized by large fluxes of film forming-species. Preferred O incorporation takes place in a region of low plasma density where small fluxes are present, when the growing surface is blocked from the arc source by the substrate holder. Hence, compositional modulations are caused by substrate rotation as the growing coating surface is periodically exposed to regions of high plasma density and large fluxes of film-forming species and regions of low plasma density and small fluxes. These findings are highly relevant for all reactive industrial plasma assisted physical vapor deposition processes utilizing substrate rotation. [ABSTRACT FROM AUTHOR]

The surface oxidation of TiAlN High Power Pulsed Magnetron Sputtering (HPPMS) hard coatings was investigated using a combined electrochemical and electron spectroscopic approach. The reversible and irreversible surface redox reactions as well as the resulting surface electronic properties were investigated by means of Cyclic Voltammetry (CV) and Electrochemical Impedance Analysis (EIS). X-ray Photoelectron Spectroscopy (XPS) of the TiAlN near-surface region as oxidised in air after deposition revealed a duplex surface film consisting of oxynitridic TiAl(O,N) covered by a shallow Al rich oxide layer. Complementary EIS revealed metallic conductivity of this TiAl(O,N) phase. A detailed microscopic model of the electrochemical oxidation process highlighting the importance of O interstitials for the oxidation process is presented. The electrochemical oxidation induced by CV resulted into a transition from metallic to n-type semiconducting properties of the surface oxide film. As disclosed by XPS and XPS sputter profiling, a complex multi-layered film was formed comprising segregated a-(TiO 2 ) x (Al(OH) 3 ) y located on top of a more ordered electrochemically inactive oxide film. Further, an intermediary nitrogen doped but segregated a-(TiO 2 ) x (Al(OH) 3 ) y :N phase was also observed. The results are of high importance for understanding the electrochemical oxidation and corrosion resistance of these hard coatings. [ABSTRACT FROM AUTHOR]

LaCr1− xCo xO3 solid-solution ceramics ( x = 0.0-0.3) were prepared by pressureless sintering of a submicrometer powder. The powder was synthesized by a modified glycine nitrate process at 800°C. The electrical conductivity of the material sintered at 1600°C was measured by AC four-wire method from room temperature to 1200°C. While undoped ( x = 0) LaCrO3 revealed semiconductivity dominated by thermally activated mobility of small polarons over a vast temperature range, substitution of Co for Cr gave rise for a pronounced enhancement of conductivity at temperatures >200°C. XPS analysis showed that the concentration of Cr4+ on the Cr-site and Co2+ at the Co-site increased with Co substitution suggesting a thermally activated redox reaction Cr3+ + Co3+→Cr4+ + Co2+ to create additional charge carriers. Thus, Co doping offers a high potential for designing the electrical conductivity making LaCr1− xCo xO3 an interesting resistivity material for high temperature applications. [ABSTRACT FROM AUTHOR]

A method to estimate the activation energy for surface diffusion during magnetron sputtering based on experimental metastable phase formation data has been developed. The so obtained activation energies are consistent with diffusion activation barriers determined by ab initio calculations. The here adopted comparative experimental and theoretical research strategy enables the efficient acquisition of activation energy data and constitutes an improved description of surface diffusion processes of metastable materials during magnetron sputtering. [ABSTRACT FROM AUTHOR]

The impact of oxygen additions on phase stability and elastic properties of titanium aluminum nitride is studied by ab initio calculations. Fcc-Ti0.5Al0.5N and fcc-Ti0.5Al0.5O show a negative energy of mixing with an interaction parameter ΩTiAlNO of -37.6 kJmol-1. The lattice parameter of Ti0.5Al0.5N1-xOx increases with increasing x while the bulk modulus decreases by 35%. The reason is the metallic bonding character which increases at the expense of the covalent character with increasing oxygen content. It is shown that the incorporation of oxygen in Ti0.5Al0.5N1-xOx on interstitial sites is energetically favourable. This can be understood based on the compensation of metallic bonding as the population of metal-oxygen bonds that are similar to a-Al2O3 and rutile-TiO2 is increased. Based on the oxygen incorporation-induced stability increase of Ti0.5Al0.5N1-xOx+y, a new design concept for transition metal oxynitride based hard coatings is developed. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen incorporation in the MAX phases Ti2AlC, V2AlC and Cr2AlC was studied by ab initio calculations. Comparing the calculated energies for oxygen incorporation indicates that oxygen substitutes for carbon in Ti2AlC and V2AlC, but is incorporated interstitially in the Al layer of Cr2AlC, even for carbon-deficient Cr2AlC. To evaluate these predictions, combinatorial d.c. sputtering was used to deposit thin films with different oxygen concentrations. Two phase regions of Cr2AlC and Cr2Al were investigated in order to study oxygen incorporation in carbon-deficient Cr2AlC. X-ray strain analysis data indicate that the a and c lattice parameters increase with oxygen content. These trends are in good agreement with the change in lattice parameters predicted by ab initio calculations and therefore corroborate the notion of interstitial oxygen incorporation in Cr2AlC. A metastable solubility limit for oxygen of 3.5at.% was determined experimentally. This is the first report on interstitial oxygen in a MAX phase and may be of relevance during the initial stages of oxidation. [Copyright &y& Elsevier]

Abstract: X-ray amorphous V2AlC and hexagonal (V,Al)2Cx thin films were synthesized by magnetron sputtering from a compound target with the composition of V2AlC. The crystallization kinetics was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). During continuous heating up to 1200°C, one exothermal peak is observed between 565 and 675°C. XRD data suggest that the DSC peak is associated with the formation of V2AlC. The activation energy of crystallization of V2AlC is ~308kJ/mol based on the Kissinger approach. This value is close to the 287kJ/mol activation energy obtained here for the transformation of magnetron sputtered (V,Al)2Cx thin films to V2AlC. The here reported phase formation temperature of V2AlC is about 800°C lower than during hot pressing of elemental powders. [Copyright &y& Elsevier]

Abstract: Amorphous Cr2AlC thin films were produced by room temperature magnetron sputtering on NaCl substrates with subsequent dissolution of the NaCl. The crystallization kinetics of Cr2AlC was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Two exothermal reactions are observed during DSC up to 1200°C. Comparing lattice parameters obtained from XRD and ab initio calculations it is suggested that the first reaction is associated with the formation of hexagonal (Cr,Al)2Cx, while after the second reaction Cr2AlC is formed. The activation energy for the phase transformations are 426 and 762kJ/mol, respectively. [Copyright &y& Elsevier]

An extension of the rule of mixture (ROM) to the sub unit-cell level is reported. This approach—which was tested for MAX and M n Al4C3+ n phases—provides a reliable estimate of the bulk moduli of single phases with layered crystal structure based on the calculated moduli of the constituents. Based on the ROM, density functional theory combinatorics is developed, reducing the calculation time for elastic properties by some orders of magnitude. This is a significant step towards knowledge-based materials design since elastic properties can be predicted based on an efficient high-throughput methodology. [Copyright &y& Elsevier]

The method of constrained equilibria has already found extensive use for a good number of years in conjunction with the programmers library ChemApp and freely adaptable ASCII based thermodynamic datafiles. In the present paper a method is demonstrated which permits the application of this method in the framework of the Integrated Thermodynamic Databank System (ITDS) FactSage. Both, modules which interact with the databases and modules which carry out thermodynamic calculations are used, thus emphasizing the aspect of integration in the ITDS. In the paper a link will be established between original thoughts by J.W. Gibbs concerning the definition of the components of a system and kinetic inhibitions in the system and the method of constrained equilibria as such. Furthermore, reference is made to Mats Hillerts use of driving forces in complex (non-)equilibrium cases. A number of application cases with different degrees of complexity will be demonstrated. These range from partially or fully constrained complex equilibrium calculations to phase diagrams with new types of axis variables. [ABSTRACT FROM AUTHOR]

The influence of oxygen content and transition metal valence electron concentration on the phase stability and elastic properties of cubic M0.5Al0.5N1-xOx (M = Sc, Ti, V, Cr; x = 0 - 0.5) was studied using ab initio calculations. The negative value of enthalpy of mixing was observed for all phases indicating full miscibility of M0.5Al0.5N with the hypothetical M0.5Al0.5O. Bulk moduli are decreased as x in M0.5Al0.5N1-xOx is increased. This can be understood based on the electronic structure. As N is substituted by O, there are no noticeable changes in the chemical bonding nature. However, O is more electronegative than N, giving rise to an increase in the ionic character of the overall bonding. In spite of that, the M - O bond in M0.5Al0.5N1-xOx is longer than the corresponding M-N bond, which implies that this bond becomes weaker. Hence, we propose that the decrease of bulk moduli upon O incorporation into M0.5Al0.5N1-xOx is caused by weaker M-O bonds. [ABSTRACT FROM AUTHOR]

Decomposition of Cr 2 AlC deposited onto a Zr substrate and vacuum-annealed is observed at 800 °C as Al diffuses from the MAX phase into the Zr substrate. A double layer of ZrN and AlN has been predicted by CALPHAD calculations to act as diffusion barrier between the Zr substrate and Cr 2 AlC. Experimental thermal stability investigations corroborate this prediction by confirming that the proposed double layer diffusion barrier coatings suppress the decomposition of Cr 2 AlC for one hour at temperatures of up to 1000 °C. [ABSTRACT FROM AUTHOR]

Since the early days of phase diagram calculation, the CALPHAD community has accepted a method of data assessment that is based on using Gibbs energy expressions for stoichiometric compounds that consist of a part that represents the contributions of the reference components, the so-called Neumann-Kopp sum, and a part that represents the Gibbs energy of formation. Usually, the latter consists only of a simple A + B * T term, which implies on the one hand that enthalpy and entropy of formation of a compound are temperature independent, and on the other, that the heat capacity of the respective compound is given by the Neumann-Kopp sum of the Cps of the constituents. In most cases this method yields acceptable results, also for the heat capacity. However, if certain elementary components are involved, this is not so. The paper highlights the problem outlining a remedial treatment that can be applied to problematic heat capacity functions present in pre-existing assessments, and thus giving a suggestion of how to prevent the problem in the future. [ABSTRACT FROM AUTHOR]

A method to model the metastable phase formation in the Cu–W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu–W and Cu–V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering. [ABSTRACT FROM PUBLISHER]

The phase stability of (Cr1−x, Mx)2(Al1−y, Ay)(C1−z, Xz) (M = Ti, Hf, Zr; A = Si, X = B, space group P63/mmc, prototype Cr2AlC) was studied using ab initio calculations. Based on the energy of mixing data as well as the density of states (DOS) analysis, (Cr1−x, Zrx)2AlC and (Cr1−x, Hfx)2AlC are predicted to be unstable, whereas (Cr1−x, Tix)2AlC, Cr2(Al1−y, Siy)C and Cr2Al(C1−z, Bz) are predicted to be stable or metastable. The density of states analysis reveals that small differences in the position of the Fermi level alters the phase stability: (Cr1−x, Zrx)2AlC and (Cr1−x, Hfx)2AlC are predicted to be unstable or metastable as the Fermi level lies at a peak position. While the Cr dominated DOS for (Cr1−x, Tix)2AlC plateaus at the Fermi level indicating stability. Implications of these results for the vapour phase condensation of self-healing Cr2AlC based materials are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The chemisorption of oxygen on TiAlN was studied at low oxygen partial pressures of 1×10−3 mPa. [•] The temporal evolution of the surface chemistry was investigated by means of time resolved XPS. [•] The process of oxygen chemisorption on TiAlN was simulated by ab initio molecular dynamics. [•] The experimental and theoretical data imply that Ti and not Al determines the oxygen chemisorption process. [ABSTRACT FROM AUTHOR]

Abstract: The energetics of point defects and twins in MC x (x <1, M =Ti, V, Cr, space group ) was studied using density functional theory. Our goal is to contribute towards understanding the underlying atomic mechanisms enabling the Al intercalation into MC x . As the valence electron concentration is increased by substituting Ti in TiC x with V and further with Cr, the energy of formation for C vacancies is decreased. This may be understood based on the electronic structure. Upon increasing the valence electron concentration, the bonding becomes less ionic and more covalent. In covalent crystals, directional bonding may be rearranged and local relaxation is observed upon vacancy creation, while this gives rise to repulsive Coulomb forces in ionic crystals, and hence the energy of formation is expected to decrease as the valence electron concentration of M is increased. The difference between the energy of formation for an Al substitution at a C site and a C vacancy, the migration energy for Al, the point defect ordering energy, and the twin boundary energy may be overcome, for instance, during vapor phase condensation. These results may be of general relevance for the formation of MAX phases (space group P63/mmc) at low temperatures. [Copyright &y& Elsevier]

The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB14 together with the (Y,Al)B6 impurity phase, containing 1.8 at. % less B than AlYB14, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB14 and cubic (Y,Al)B6 phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions. [ABSTRACT FROM AUTHOR]

Through the judicious use of "virtual elements" that have zero atomic mass but that are included in the materials balances, it is possible to apply a variety of constraints to chemical equilibrium calculations without the necessity of writing dedicated software for each individual application. Several examples are presented, including the suppression of decomposition of metastable molecules and ions or redox reactions in aqueous solutions, the suppression of internal equilibria in molten salts and ceramics, the calculation of the surface tension of solutions, following the course of reactions with time, paraequilibrium calculations and limiting the extent of a reaction. • Constrained chemical equilibrium calculations through use of virtual elements. • Suppression of internal sub-lattice equilibria in chemical equilibrium calculations. • Suppression of redox equilibria in chemical equilibrium calculations. • Applying equilibrium constraints with FactSage software. [ABSTRACT FROM AUTHOR]

The effect of Si additions on the oxidation behavior of Cr 2 AlC based coatings is investigated. Oxidation experiment was performed at 1120 °C in air for 4 h for Cr 2 AlC and Cr 2 Al 1 − x Si x C (0 < x ≤ 0.06) coatings. The crystal structure, microstructure and chemical composition of the as-deposited as well as oxidized coatings have been investigated. Alloying Cr 2 AlC with up to 0.7 at.% Si causes an increase in Al 2 O 3 scale thickness by up to 40 ± 17%. Electron microscopy and atom probe tomography data support the notion that the here reported Si concentration induced 40% increase in Al 2 O 3 layer thickness (during oxidation at 1120 °C for 4 h) is enabled by the Si concentration induced, and hence concomitant, increase in nucleation density of Al 2 O 3 . [ABSTRACT FROM AUTHOR]

• Thermodynamic modeling of an entire reciprocal system using a single subregular model for the liquid phase. • Thermodynamic modeling of the liquid solution spanning from water to liquid acid and base, and liquid salt as a single phase. • Excellent representations of the phase diagrams and properties of the liquid phase in all binary sub-systems. Over the last few decades, thermochemical databases for aqueous solutions and for high-temperature salt solutions have been developed separately from each other. This is largely due to the fact that the models used for the liquid phases are inconsistent. However, there is interest in highly concentrated aqueous solutions, as well as in the hydrolysis of salt melts, closing the gap between the two communities. Here, the liquid phase was consistently modeled, covering the complete composition space between H 2 O, HCl, KOH, and KCl at temperatures between 200 K and 1,000 K. Thermodynamic modeling of phase equilibria in the KCl–K 2 O–HCl–H 2 O reciprocal system was carried out using an associate solution model for the liquid phase, spanning from water to pure liquid acid and base, and liquid salt. Using the Calphad technique, the H 2 O–KCl, H 2 O–HCl, H 2 O–K 2 O, and KOH–KCl binary systems were critically assessed. While the model does not cover classical aqueous thermochemical properties (pH and osmotic coefficient), an excellent representation of phase diagrams and heat of reactions was achieved. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the influence of transition metal (M =Ti, Cr) and nonmetal (N, O) valence electron concentration, surface defects, and radicals on the interaction of polypropylene and cubic M 0.5Al0.5N (002) and (111) surfaces using ab initio calculations. For the ideal and defected surface, the work of separation is low and not affected by valence electron concentration, implying weak interactions. Striking differences occur for radicals, where an increase by two orders of magnitude is observed. This may be understood based on the electronic structure. Radicals give rise to strong bonding across the interface and hence strong interactions. [Copyright &y& Elsevier]

Vanadium oxides were added to the existing GTOx database because of its important role in the ferro-titanium metallurgy as well as in petroleum coke gasification. The CaO–FeO–Fe 2 O 3 –MgO–SiO 2 system is a part of GTOx database and is chosen because of the existence of experimentally determined vanadium distributions between vanadium ferroalloys and metallurgical slags. The CaO–FeO–Fe 2 O 3 –MgO–SiO 2 –V 2 O 3 –V 2 O 5 system including all binary and ternary sub-systems was thermodynamically assessed using all available experimental data. Vanadium was introduced into the thermodynamic description of solid solution phases such as MeO, Spinel, Corundum and Ca 2 SiO 4 -α using available experimental information. Particular attention was given to the phase Spinel which forms the wide completely miscible solid solution Fe 3 O 4 –FeV 2 O 4 –MgV 2 O 4 –MgFe 2 O 4. The thermodynamic description of the metallic vanadium containing systems was taken from the SGTE alloy database. With the knowledge about the complex behavior of vanadium in slags as well as in liquid metal alloys it is possible to calculate the vanadium distribution ratios (V)/[V] between iron melts and slags in a wide range of temperatures and compositions, corroborating the validity of the model under reducing conditions. The additionally developed viscosity model shows good agreement between the calculated and experimental values in vanadium-containing slags. [ABSTRACT FROM AUTHOR]

• Zinc condensation behavior is investigated under gasification conditions. • Influence of the (HCl/H 2 S) gas mixtures on zinc condensation behavior is studied. • Scheil-Gulliver cooling model provides a good reference for condensation analysis. • The mechanisms for zinc condensation processes in gas mixtures are proposed. • Potential applications in IGCC power plants and future directions are discussed. Fuels used in combustion and gasification, such as coal, biomass and wastes, yield large amounts of trace elements, which can cause both technological and environmental concerns. This work provides an in-depth insight into the condensation behavior of the trace element zinc under gasification-like conditions in atmospheres containing the HCl and H 2 S trace gases. A lab-scale quartz reactor with a multi-stage cooling zone was used to determine the condensation content and species distribution of the zinc deposition in different gasification atmospheres. The Scheil-Gulliver cooling model was used to simulate the zinc condensation process, since it provides a good reference to analyze the degree of supercooling during the condensation process. Competition of the gaseous species HCl and H 2 S with respect to the ZnO condensation behavior has been observed. HCl leads to significant supercooling of the ZnO condensation. It is shown that this can be compensated by ZnS acting as nucleation sites for ZnO if significant amounts of H 2 S are present. It is further shown that there is a significant bypass effect, i.e. even after nucleation has started there is a significant amount of Zn remaining in the gas phase which significantly extends the condensation regime to lower temperatures. To visualize both effects, a H 2 S-temperature-transition diagram is proposed. The potential applications including the prevention of problematic depositions (slagging and fouling) and sorbent selection as well as design for removal of trace element zinc from the syngas in IGCC power plants are proposed and discussed in the light of developing clean power technologies. [ABSTRACT FROM AUTHOR]