Mn3−xZnxO4 spinel phases in the Zn–Mn–O system

The thermal evolution of the Zn–Mn–O system in air was studied by X-ray diffraction, transmission electron microscopy–energy dispersive spectroscopy and electron energy loss spectroscopy. The obtained results suggest that this evolution involves the formation of different Mn_3−xZn_xO₄ spinel-type phases. With increasing temperature these spinels experience phase transformations which are found to be induced by the Mn(IV) to Mn(III) reduction process. This last cation is an active Jahn–Teller ion which leads to an appreciable distortion of the Mn_3−xZn_xO₄ spinel structure, from a cubic symmetry at low temperatures to highly distorted tetragonal symmetries at high temperatures.     

The compositional range of amorphous phase formation and thermal stability of Al90−xFe5Ni5Cex

The effects of Ce-substitution for Al in the Al_90−xFe₅Ni₅Ce_x (x = 0, 2, 5, 7, 8, 9, and 10) system on the mechanical alloying process were investigated. The structural evolution in these powders was characterized by scanning electron microscopy, differential thermal analysis and X-ray diffraction techniques. The compositional range of amorphous forming was obtained and it extended from 5 to 9 at.% Ce. With increasing Ce content, the crystallization temperature of amorphous alloys increases. The crystallization temperature versus concentration of Ce was reproduced well by applying an extension of a relationship between the crystallization temperature and the vacancy formation energy of constituents with smaller atomic radius. The crystallization product phases were analyzed by XRD after annealing the milled powders at temperature over the crystallization temperature.     

The 400 °C Isothermal Section of the La-Co-Mg Ternary System

The isothermal section of the La-Co-Mg system at 400 °C was determined by characterization of about thirty ternary alloys synthesised by induction melting in sealed Ta crucibles and then annealed. Scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDXS) and x-ray powder diffraction (XRPD) were used to analyze microstructures, identify phases, measure their compositions and determine their crystal structures. Phase equilibria are characterized by the absence of ternary solid solutions and by the presence of three ternary phases. The existence and the crystal structure of the La_4?x CoMg_1 + x (τ₁, 0 ≤ x ≤0.15, cF96-Gd₄RhIn) were confirmed and its homogeneity region determined; the new phases La_23?x Co₇Mg_4 + x (τ₂, ?0.50≤ x ≤0.60, hP68-Pr₂₃Ir₇Mg₄) and ~La₃₈Co₅₅Mg₇ (τ₃, unknown crystal structure) were detected.     

Ternary rare earth (R) alloys occurring in RAu2-RGa2 sections

Ternary alloys of the rare earths with gold and gallium, at the stoichiometric ratio 1:0.5:1.5, were synthesised and structurally determined. New compounds were identified for R=Nd, Sm, Gd, Tb, Dy, Ho Er, Y and their crystal structures were found to be related to the hexagonal CaIn₂ type. A homogeneous alloy was obtained for Yb too, and was found to crystallise in the orthorhombic oI12-CeCu₂ type structure. The stability composition range of CaIn₂ type was analysed in the GdAu_2−xGa_x system: the CaIn₂ type phase was found to exist for x values ranging between 1.4 and 1.55. For higher and lower x values, phases crystallising in the hP3-AlB₂ and oI12-CeCu₂ type structure, respectively, were observed.     

Modeling of phase stability of the fcc phases in the Ni–Ir–Al system using the cluster/site approximation method coupling with first-principles calculations

A combined CSA (cluster/site approximation)/FP (first-principles) calculation approach was employed to investigate the phase stability and thermodynamic properties of the face-centered cubic (fcc) phases of the Ni–Ir–Al system. For the constituent binaries of the Ni–Ir–Al system, enthalpies of formation of the Ni_xIr_1−x, Ni_xAl_1−x and Ir_xAl_1−x fcc compounds were calculated by first-principles approach at x = 0.75, 0.5 and 0.25 at 0 K, respectively. The pair exchange energies of the Ni–Ir and Al–Ir systems in the CSA model were obtained from FP calculated enthalpies of formation, while those for the Ni–Al binary were adopted from previous work. Thermodynamic model parameters of the fcc phases for the Ni–Ir–Al ternary system were then obtained from the constituent binaries via extrapolation. The calculated isothermal section at 1573 K is in good agreement with the experimental data within the uncertainties of the calculations and experiments.     

Potential energies of characteristic atoms on basis of experimental heats of formation of AuCu and AuCu3 compounds （ Ⅱ ）

The potential energy sequences of characteristic atoms were separated out by nine potential energy E-functions on the basis of larger experimental heats of formation of the L1₀-AuCu and L1₂-AuCu₃ compounds only. According to these potential energy sequences of characteristic atoms, the potential energies and heats of formation of disordered Au_1−xCu_x alloys were calculated by corresponding E-functions at 0 K; and the potential energies, heats of formation and critical T_c-temperatures of the order-disorder transitions of L1₀-AuCu, L1₂-Au₃Cu and L1₂-AuCu₃ compounds, Au₃Cu-, AuCu- and AuCu₃-type ordered alloys with maximal ordering degrees were also calculated at 0 K. The results obtained by both the first and present parts of this investigation were compared. Comparing the results obtained by nine E-functions, the 5th E(x, 0, σ) function may be chosen for describing thermodynamic properties of the compounds, ordered and disordered phases and for establishing the phase diagram of the Au-Cu system in the future.     

Thermodynamic assessment of the Ga–Pt system

The Ga–Pt binary system has been thermodynamically assessed by means of the computer program Thermo-Calc. The Redlich-Kister polynomial was used to describe the solution phases, liquid (L) and fcc (Pt). The compounds, Ga₆Pt, Ga₇Pt₃, Ga₂Pt, Ga₃Pt₂, GaPt, Ga₃Pt₅ and GaPt₂, were treated as stoichiometric phases. The sublattice-compound energy model was employed to describe the compound GaPt₃, with a homogeneity range. The parameters of the Gibbs energy expressions were optimized according to all the available experimental information of both the equilibrium data and the thermodynamic results. A set of self-consistent thermodynamic parameters of the Ga–Pt system has been obtained. The calculations agree well with the respective experimental data.     

Crystallization kinetics of new compound of V2O5–PbO–Li2O–Fe2O3 glass using differential thermal analysis

Different glasses with nominal compositions of (70 − x)V₂O₅–xPbO–20Li₂O–10Fe₂O₃ (0 ≤ x ≤ 12.5 mol.%) were successfully obtained by the melt quenching technique. Crystallization kinetics of these glasses was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The procedure was applied to the experimental data obtained by differential thermal analysis, using several measurements at different heating rates. In addition, from the heating rate dependence of the glass transition temperature, the glass transition activation energy was derived. The crystallization results are analyzed and both the activation energy of crystallization process and the crystallization mechanism are characterized in terms of Gao–Wang method. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material indicates the presence of microcrystallites of LiV₁₅O_35.5, Pb₃(VO₄)₂ and PbO₂ beside the remaining an additional amorphous matrix.     

Self-propagating high-temperature synthesis of (Zr,W)C/WC/Al2O3 composite powders from WO3-ZrO2-Al-C system

In the present study, the self-propagating high-temperature synthesis of 2(1-x)WO₃-3xZrO₂-Al-2(1 + 0.5x)C system was considered to prepare WC-ZrC-Al₂O₃ composite powders. The effects of an increase in the x-value between 0 and 1 as well as the addition of 50 wt% extra carbon to the initial reactant mixture on the adiabatic temperature, reaction front velocity, structure and microstructure of the combustion products were investigated. Results showed that the adiabatic temperature and the reaction front velocity decreased with increasing the x-value until it reached zero for x = 0.5. For x = 0 sample, WC, W₂C and W phases were formed after the synthesis process. The addition of extra carbon led to an increase in the (WC + W₂C)/W ratio. Furthermore, (Zr,W)C/WC/W₂C/Al₂O₃ composite powders were obtained for x > 0. Moreover, the (Zr,W)C concentration with near-stoichiometric composition and blocky morphology increased with the x-value. Differential thermal analysis results illustrated that the SHS reaction in the WO₃-ZrO₂-Al-C system is initiated by the aluminothermic reaction of WO₃. Moreover, it was postulated that the presence of W facilitated the formation of zirconium carbide.     

Thermodynamic assessment of the Al–Pd system

The Al–Pd binary system has been thermodynamically assessed by means of the computer program Thermo-Calc. The Redlich–Kister polynomial was used to describe the solution phases, liquid (L) and fcc. The sublattice-compound energy model was employed to describe the intermetallic compounds with homogeneity ranges, (AlPd), (AlPd₂), (Al₃Pd₂) and (Al₂Pd₅). The intermetallic compounds with no homogeneity ranges, Al₃Pd, Al₂₁Pd₈, Al₄Pd and Al₃Pd₅, were treated as stoichiometric phases. The parameters of the Gibbs energy expressions were optimized according to all the available experimental information on both the equilibrium data and the thermodynamic results. A set of self-consistent thermodynamic parameters of the Al–Pd system has been obtained. The calculations agree well with the respective experimental data.     

Phase stabilities and spinodal decomposition in the Cr1−xAlxN system studied by ab initio LDA and thermodynamic modeling: Comparison with the Ti1−xAlxN and TiN/Si3N4 systems

The total energies and lattice constants of binary hexagonal close-packed (hcp)- and face-centered cubic (fcc)-CrN, AlN and ternary Cr_0.5Al_0.5N phases are calculated using the Vienna Ab-initio Simulation Program. The calculated total energies of the structures are then used to calculate the lattice stabilities of binary hcp- and fcc-CrN and AlN, and the interaction parameters of the ternary hcp- and fcc-Cr_1−xAl_xN solution phases. These results are used in the sublattice thermodynamic model to construct the Gibbs free energy diagram of the immiscible quasi-binary CrN–AlN system at different temperatures. Based on these results, we discuss the relative phase stability of the metastable ternary hcp- and fcc-Cr_1−xAl_xN solid solutions over the entire range of compositions. The predictions are compared with and supported by the published results from physical and chemical vapor deposition experiments. The constructed Gibbs free energy diagrams show that metastable fcc-Cr_1−xAl_xN coatings may undergo spinodal decomposition into coherent fcc-CrN and fcc-AlN, but there is a relatively large barrier for a direct formation of the stable hcp-AlN. A comparison with the Ti_1−xAl_xN and TiN–Si₃N₄ systems shows that the phase segregation will be more difficult and, therefore, the solid solution more stable in the Cr_1−xAl_xN case.     

Phase stabilization in the Fe1−xMnxSi2 system induced by ball milling

Phase formation in the Mn doped iron disilicide system Fe_1−xMn_xSi₂ with 0.00 ≤ x ≤ 0.24 was studied using X-ray diffraction and Mössbauer spectroscopy. Samples were prepared at room temperature in Ar atmosphere by two different routes. The first one involved the simultaneous mill of the pure elements, and the second one the milling in two steps, first the premixture of metals and then the addition of Si. Both routes produced β-FeSi₂, ɛ-FeSi and α-FeSi₂ phases. In the first case, the segregation of MnSi and Si was also observed. The diffraction results and the obtained set of hyperfine parameters supported the coexistence of β-FeSi₂, α-FeSi₂ and ɛ-FeSi. The relative phase composition depended on the preparation route, being the obtained fraction of the ɛ-FeSi smaller when the second preparation route was followed. It seemed that the previous formation of a Fe_1−xMn_x alloy before to the silicide overcomes the chemical driving forces.     

New TiNiSi-type RMgAg and RMgPd with R=Ca, Yb, and MgZn2-type Ca(Mg,Ag)2 compounds

The phases CaMgAg, YbMgAg, CaMgPd, and YbMgPd were synthesized by melting the constituent metals in sealed tantalum crucibles and by annealing at 1023 K. All the samples were homogeneous, and the crystallographic analysis, which was performed by powder and singlecrystal techniques, shows that the four compounds are isotypic and belong to the orthorhombic TiNiSi type. Magnetic measurements showed that YbMgAg and YbMgPd behave like Pauli paramagnets, according to the divalency of Yb in both phases. Within the Ca-Mg-Ag system, the existence range of the MgZn₂-type phases in the Mg-rich CaMg_2−x Ag _x pseudobinary system goes from CaMg₂ to CaMg_1.6Ag_0.4. Another stability region of the MgZn₂ structure occurs around the Ag-rich composition (Ca_0.94Mg_0.06)(Ag_1.60Mg_0.40), where magnesium replaces both the Ca and Ag atoms.     

Experimental Investigation of the Al-Fe-Nd System at 773 K

The phase diagram of Al-Fe-Nd is helpful for development of the magnetic and amorphous materials based on this system. The entire isothermal section of Al-Fe-Nd at 773 K was determined by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive analysis (EDX) and optical microscopy (OM). The existences of 12 binary compounds of the Al-Fe, Al-Nd and Fe-Nd systems were confirmed, and binary phases Al₂Nd and Fe₁₇Nd₂ demonstrated appreciable ternary solubility. The ternary compounds: τ₁-Al₁₀Fe₂Nd, τ₂-Al_8+x Fe_4?x Nd (0 < x < 0.7) and λ-Nd₃₀Fe_62?x Al_8+x (0 < x < 17) were confirmed in the present work. The isothermal section consists of 18 single-phase regions, 36 two-phase regions and 19 three-phase regions.     

Synthesis of CaNi1−xPdx (0.1≤x≤1) alloys and hydrogenation properties of CaPd

An evaluation of the substitution of a third element for the constituent elements (Ca, Ni) in the compound was conducted in order to obtain information about stabilization of the CaNi compound which does not exist as a stable phase. Prior to the experimental study of the substitution, the candidates for the third element were investigated using Miedema’s semi-empirical model, from the standpoint of formation enthalpy, and as a result, Pd was chosen as the element to stabilize the compound. The samples with the nominal compositions of CaNi_1−xPd_x (0.1≤x≤1) were prepared by sintering and high frequency heating, and the constituent phases and hydrogenation properties were examined. New ternary phases such as Ca₁(Ni, Pd)₁ were not obtained under the present conditions; however, some pieces of new information such as the substitution of Ni for Pd in CaPd₂ and reversible hydrogenation of CaPd at 373 K were obtained through the studies.     

The CaO-SrO-CuO-O2 system: Phase equilibria and thermodynamic properties at 1123 K

Phase relationships in the CaO-SrO-CuO system in pure oxygen at 1.01 × 10⁵ Pa pressure were determined by equilibrating different compositions at 1123 K for ～120 h and analyzing the phases present in the quenched samples using X-ray diffraction (XRD), optical and scanning electron microscopy, and energy dispersive analysis of X-rays (EDAX). Four solid solution series were observed in the system. The Ca_wSr_1-wO monoxide solid solution with rock-salt structure was found to exhibit an asymmetric miscibility gap. The mixing properties of the monoxide system were deduced using a subregular solution model. For the (Ca_xSr_1-x)₂CuO₃ series, a complete solid solution range with orthorhombic space groupImmm was obtained. Calcium substituted for strontium up to 68 at.% in SrCuO_2+δ and 51.5 at.% in Sr₁₄Cu₂₄O_41-δ. The tie lines between the solid solutions were determined accurately. The activity-composition relations in (Ca_xSr_1-x)₂CuO₃, Ca_ySr_1-y,CuO_2+δ, and (Ca_zSr_1-z)₁₄Cu₂₄O_41-δ solid solutions were determined from experimental tie lines. Activities in the (Ca_xSr_1-x)₂CuO₃ and Ca_ySr_1-yCuO_2+δ series were close to the predictions of the Temkin model. The behavior of the (Ca_zSr_1-z)₁₄Cu₂₄O_41-δ solid solution was more complex, with the activity of SrCu_(24/14)O_(41-δ)/14 exhibiting both positive and negative deviations from ideality. Gibbs energy of formation of the CaCuO_2+δ metastable phase at 1123 K was deduced from an analysis of the phase diagram.