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The C15 phase (Fd3¯m) has been extensively studied by several methodologies to evaluate its atomic interactions. Ideally ordered at the AB2 composition, this Laves phase is known to present a non-stoichiometry domain accommodated by substitutional atomic disorder at high temperature. With the Cu-Mg system as an example, a cluster expansion method study revealed that first neighbors pair interaction is positive yielding a favorable mixing of Cu and Mg atoms in 16d site and a homogeneity extended in the Mg-richer side. To guide the thermodynamic modeling of the C15 phase, special quasi-random structure cells have been generated at several compositions to simulate atom mixing with and without the merging of 8a and 16d sites. Combined with electronic density functional theory, calculation on several systems (Ta-V, Cr-Nb, Mo-Zr and Cr-Ti) was done to estimate the mixing energies on the two different sublattices. The results are compared to published assessments and open a discussion on the acceptability of the traditional thermodynamic model. [ABSTRACT FROM AUTHOR]

Abstract: The solid solution based on Nb5Si3 (Cr5B3 structure type, D8 l , tI32, I4/mcm, No140, a=6.5767Å, c=11.8967Å) in the Nb–Si–B system was studied from the structural and thermodynamic point of view both experimentally and by ab initio calculations. Rietveld refinement of powder X-ray synchrotron data allowed to determine the boron to silicon substitution mechanism and the structural parameters. Ab initio calculations of different ordered compounds and selected disordered alloys allowed to obtain in addition to the enthalpy of formation of the solution, substitution mechanism and structural parameters which are in excellent agreement with the experimental data. The stability of the phase is discussed. [Copyright &y& Elsevier]

Abstract: The hydrogenation properties of the LaNi5−x M x (M =Rh, Ir, Au) compounds have been studied. The Ni substitution has several consequences: pressure plateau splitting and increase of plateau pressure. This latter observation disagrees with the general rule that a cell volume increase of the alloy should result in a plateau pressure lowering. In order to elucidate the origin of this anomalous behaviour, DFT calculations have been performed on both LaNi5−x Rh x and LaNi5−x Pt x intermetallic compounds, which, according to the present and previous experimental work, present a similar anomaly. We discuss our results in light of the models proposed in the literature. We conclude that, in the case of a Ni substitution by 4d or 5d elements, the size effect alone fails in predicting the hydrogen absorption properties while the rule of reverse stability is obeyed. [Copyright &y& Elsevier]

Abstract: The quinary system D–H–Pd–Rh–T has been described thermodynamically by the CALPHAD approach. Previous descriptions of the binary subsystems have been used. To model the high pressure data an equation of state for the gases D2 and T2 compatible with the CALPHAD approach has been obtained similar to that previously used for H2. A complete literature search has been undertaken for the three ternary systems H–Pd–Rh, D–Pd–Rh and Pd–Rh–T and the most significant experimental data have been selected for a thermodynamic assessment of these systems. In order to complement the available data, pressure–composition curves have been measured at different temperatures for the two last systems in the present work. Calculations and optimization of the system under para-equilibrium conditions, i.e. in pseudo-binary systems (Pd,Rh)–H, (Pd,Rh)–D or (Pd,Rh)–T, have been achieved using a pseudo-atom describing the Pd–Rh solid solution. This special method allows the presence of a miscibility gap in the binary metallic system to be dealt with. We show that a simple combination of the binary systems alone is unable to properly describe these ternary systems and that ternary interaction parameters have to be introduced. The binary and ternary systems may then be combined to perform calculations in the quinary D–H–Pd–Rh–T system. It is believed that extrapolation in systems containing different isotopes are fairly accurate provided that the so-called Toop model is used. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogenation properties of the LaNi5 (CaCu5 type, hP6, P6/mmm) and Pd substituted derivatives LaNi5−x Pd x compounds have been studied in the whole homogeneity range of the solid solution (0.25≤x≤1.5). The pressure versus hydrogen content isotherms show several plateaus and an increase of the plateau pressure as a function of palladium concentration. The volume increase of the Pd substituted alloys should have resulted in a lowering, and not an increase, of the plateau pressure, according to the conventional models based on the size effect. In order to elucidate the origin of this anomalous behavior, both an experimental and a theoretical ab initio electronic structure investigation have been carried out. Experimentally, the nature and the structural properties of the hydrides have been studied by both in situ and ex situ neutron diffraction. The crystal structures of the three hydride phases are reported (LaNi3.5Pd1.5D1.96, filled-up CaCu5 type, P6/mmm; LaNi4PdD2.72, LaNi2(Ni0.75Pt0.25)3H2.61 type, oI128, Ibam; LaNi4.75Pd0.25D5.67, partly ordered CaCu5 type, P6mm). In addition, the phase diagram of LaNi5−x Pd x -H system has been investigated. The electronic and thermodynamic properties of both intermetallic compounds and the hydrides have been studied by ab initio electronic structure calculations. The theoretical results are in good agreement with our experimental data, and show that electronic interactions play a major role in the hydrogenation behavior of these Pd substituted intermetallic compounds, and that these effects cannot be accounted for by a simplistic model based on the size effect alone. [ABSTRACT FROM AUTHOR]

Abstract: A new equation of state for hydrogen gas (0≤ P ≤1011 Pa, 298≤ T ≤1000K) has been derived and is given in an analytical form. It is compatible with the Calphad approach (i.e. it is an analytical equation of the Gibbs energy as a function of pressure). This equation has been applied to the Calphad assessment of the H–Rh system, an example of system forming a metal hydride only at a very high pressure. A set of self-consistent thermodynamic parameters describing the Gibbs energy of each phase has been obtained. The scarce experimental data available for this system, particularly the high formation pressure of the hydride, have been well reproduced which otherwise would have been impossible without considering the non-ideal behaviour of the gas phase. [Copyright &y& Elsevier]

Abstract: The three binary systems H–Pd, D–Pd and Pd–T have been modelled in the frame of the Calphad approach. A complete literature search has been undertaken and the most significant experimental data have been selected for a thermodynamic assessment of these systems. To complement the available data, pressure–composition curves have been measured for the three systems in the present work. The three systems are characterized by a strong isotope effect which is well taken into account in the modelling. They have been combined to perform calculations in the quaternary H–D–Pd–T system. It is shown that a reasonable extrapolation can be made without the use of ternary parameters if it is calculated with the so-called Toop model. [Copyright &y& Elsevier]

Abstract: This article is a comprehensive review devoted to the phase diagram and crystal structure properties of the χ phase intermetallic compound. An extensive study of the available literature has been performed and completed by key experimental measurements performed in the following systems: Fe–Re, Mn–Mo, Mn–Re, Mn–Ru, Mn–V, Mo–Re, Nb–Os, Nb–Re, Re–Ti, Re–Zr. The χ phase is an important Frank–Kasper (topologically close-packed) phase whose presence in certain systems has implications in the process of industrial materials such as Ni-based super-alloys. As a binary phase, it exists mainly in transition metal systems of Tc, Re and Os with elements of groups 3–6, rare earths-Mg systems and (αMn) solid solutions. It has the peculiarity to exist in three ordered variants corresponding to the different prototypes αMn, Ti5Re24 and Mg17Al12. Particular attention has been paid to the way the composition of the binary compounds is accommodated by atom mixing on the different sites. In our experimental work, occupancy parameters on the four crystallographic sites have been obtained by Rietveld analysis of X-ray powder diffraction data. The investigation has been made as a function of composition when possible. In addition to the study of the intermetallic compounds, particular emphasis has been placed on the study of the ordering in (αMn) solid solutions. This study has implications on the modelling of the χ phase with the Calphad method. Different models are reviewed and recommendations are made for future thermodynamic assessments. [Copyright &y& Elsevier]

Abstract. This review is devoted to the main families of thermodynamically stable intermetallic compounds (AB[sub 5]-, AB[sub 2]- and AB-type alloys) that have been researched in the last thirty years as materials for negative electrodes in nickel-metal hydride batteries. The crystal structure of these compounds and their hydrides is widely described. Their solid-gas hydrogenation properties and, particularly, the related desorption isotherm curves are examined as a useful criterion for the selection of suitable battery materials. The electrochemical performances obtained with these alloys are reported and the given solutions to common problems such as corrosion, passivation, decrepitation and short cycle life are discussed. Only AB[sub 5]-based compounds have achieved, up to now, enough development for being widely present on the market, and exhibit improved battery performances in comparison with the polluting Ni/Cd batteries. The high capacity of AB[sub 2]-based compounds and the remarkable electrochemical activity of some AB-based alloys make, however, further research on all the reviewed families still valuable. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogenation properties of Fe–Ti–V bcc alloys have been studied by the Sieverts method. Starting from a fully determined ternary phase diagram, a large number of compositions have been synthesized and pressure–composition–isotherms have been measured at different temperatures both in the low and high hydrogen concentration regions. The enthalpies of absorption and desorption have been found to vary linearly as a function of composition in the ternary domain and depend on the ones of the pure elements. The absorption capacity is mainly dependent on the iron concentration. Additionally, the crystal structure of the hydrides has been studied. For the first time a progressive and continuous distortion from body centered cubic (bcc) to body centered tetragonal (bct) structure has been evidenced. [Copyright &y& Elsevier]

Abstract: The erbium–zirconium (Er–Zr) system has been completely reinvestigated experimentally. Particular attention was paid to the high purity of the raw materials, to the absence of oxygen contamination and to the control of the high vapor pressure of erbium. Several experimental techniques have been used to measure the solubility limits at different temperatures, the invariant points and the solidus and liquidus temperatures which were generally found to disagree with what was reported in the literature. As a result, the phase diagram presently obtained differs significantly from the accepted one and we propose a complete revision of the system. A thermodynamic assessment using the Calphad approach has been conducted. A set of parameters has been obtained allowing to describe well the experimental measurements. [Copyright &y& Elsevier]

Abstract: The Zr–Sn binary system has been reinvestigated by several experimental techniques: X-ray diffraction, electron probe micro-analysis, mass density and calorimetry measurements. The existence of a miscibility gap inside the homogeneity domain of the phase (Zr5Sn3–Zr5Sn4) has been confirmed. It has been also shown that Zr substitution on the Sn sublattice is responsible for the non-stoichiometry of the 15 phase (Zr4Sn). The temperature of the peritectoid reaction βZr+A15↔αZr has been determined to be at 1216 K that is below the temperature reported in the literature. All these new experimental data have been taken into account for a new thermodynamic assessment of this system. [Copyright &y& Elsevier]

Palladium, rhodium and ruthenium are abundant fission products that form in oxide fuels in nuclear reactors. Under operating conditions, these Platinum-Group Metal (PGM) fission products accumulate in high concentration at the rim of the oxide fuel and mainly precipitate into metallic solid solutions. Their thermochemistry is of significant interest to predict the high temperature chemical interactions between the fuel and the cladding or the possible precipitation of PGM phases in high level nuclear waste glasses. To predict the thermodynamic properties of these PGM fission products, a thermodynamic modeling is being developed on the ternary Pd Rh Ru system using the Calphad method. Because experimental thermodynamic data are scarce, Special Quasirandom Structures coupled with Density Functional Theory methods were used to calculate mixing enthalpy data in the solid solutions. The resulting thermodynamic description based on only binary interaction parameters is in good agreement with the few data on the ternary system. [ABSTRACT FROM AUTHOR]

Abstract: The phase equilibria and thermodynamic properties of the Mo–Re system are studied by combining first-principle and CALPHAD approach. The mixing enthalpies in the bcc and hcp solution phases are estimated by first-principle calculations using the special quasirandom structures. The liquid, bcc and hcp phases are described by a substitutional solution model. The intermetallic phases, σ and χ, are described with the compound energy formalism with, respectively, 5 and 4 sublattices (SL) using the formation enthalpies of all the end-members directly from ab initio calculations. A phase diagram in agreement with the available experimental knowledge is obtained thanks to a least square procedure involving a limited number of parameters. Introducing all the elements in all the sublattices of the structure allows a proper description of the configuration of the intermetallic phases. Different simplifications of the description of the σ phase are considered. The ideal 4SL simplification is equivalent to the full description. The 3SL and 2SL models require excess parameters in order to fit reasonably the experimental phase diagram. Among these, only the (Mo,Re)10(Mo,Re)12(Mo,Re)8 model allows to closely approximate the low temperature thermodynamic properties of the full description. [Copyright &y& Elsevier]

Abstract: A thermodynamic optimization of the Mo–Re system by the Calphad method is proposed, taking into account new experimental data obtained in this work. According to recent crystal chemistry work, the and Frank–Kasper phases were modeled using two independent sublattices of variable occupation. This was made possible by including experimental site fractions in the different sublattices as input data for the parameter optimization. A consistent set of parameters is proposed. Good agreement is found between calculated and selected experimental values for different kinds of data: phase diagram, thermodynamic and crystallographic data. [Copyright &y& Elsevier]