CsCl Type Research Articles

Alloy Constitution and Phase Equilibria in the Hf–Ru–Rh System. III. Solidus Surface of the Partial Ru–HfRu–HfRh–Rh System

The data obtained by physicochemical analysis techniques are used for the first time to determine the nature of phase equilibria in the Hf–Ru–Rh system at 50−100 at.% Hf (Hf–HfRu–HfRh partial system) at subsolidus temperatures and to construct the solidus surface on the composition triangle. It is established that there is a continuous series of solid solutions between isostructural (CsCl type) HfRu-based and high-temperature δ-HfRh phases. This allowed triangulation of the Hf–Ru–Rh system into two partial ones at 50 at.% Hf. The β-Hf solid solution, γ-Hf2Rh phase (Ti2Ni structure), and δ-phase, forming three single-phase regions on the solidus surface, participate in the phase equilibria at subsolidus temperatures. The ruled surfaces formed by the δ and δγ tie lines decrease from the bounding binary systems to theδ γ isothermal plane at 1373°C and the γ ruled surface decreases in turn to the Hf–Rh binary system.

Pressure induced phase transition and thermo-physical properties in LuX (X = N, P)

Detailed total energy calculations have been performed in lutetium pnictides (LuX, where X = N, P) to understand their high pressure structural stability. In LuN, the ambient rocksalt type structure (B1 phase) transforms to a tetragonal structure (B10 phase) at ∼240 GPa; whereas in LuP the orthorhombic structure (B33, space group Cmcm) emerges as a high pressure structure above 48 GPa. Both the transitions are found to be of first-order type with volume discontinuities of ∼6% and 8.2%, respectively. The high pressure phases B10 and B33 are found to be stable up to 400 GPa, respectively. Further, the structural stability predicted from static lattice calculations has been supported by lattice dynamical stability analysis. The present calculations rule out the B1 to B2 (CsCl type) structural phase transitions predicted to occur at 241 GPa in LuN and at 98 GPa in LuP by previous all-electron calculations (Gupta and Bhat 2013 J. Mol. Model 19 5343–54). The temperature dependence of several thermo-physical properties such as volume, bulk modulus, specific heat and thermal expansion coefficient of the rocksalt structure of these compounds calculated in the present study, using quasi-harmonic approximation, awaits confirmation by experimental studies.

Formação de Fases Quasicristalinas No Sistema Al65Cu20Fe15

<p>Características estruturais, morfológicos e fases existente na liga quasicristalina com composições nominal de Al65Cu20Fe15 foram investigados por difração de raios-X (DRX), Microscopia Eletrônica de Varredura (MEV)/ Espectroscopia de Energia Dispersiva (EDS), Calorimetria Exploratória Diferencial (DSC) e Área Superficial Específica (BET). Os resultados mostram que foram observados vários aspectos morfológicos das fases quasicristalinas em função da sua obtenção em fornos elétricos a indução e a arco em condições experimentais em que ambas as fases cristalinas e quasicristalinos coexistem à 850°C. Quando a perda de alumínio no interior dos grãos é demasiado elevada, a fase icosaédrica transforma em fase ? cúbica (tipo de CsCl). Devido aos eventos térmicos (exotérmico) numa faixa 400-1200°C apresentando aumento do número de fase e a área superficial apresentar um ótimo candidato,podendo ser usado como catalisador em reações catalíticas devido a sua estabilidade térmica. Finalmente futuras aplicações atuais e possíveis de quasicristais Al-Cu-Fe são discutidos à luz de suas propriedades.</p>

Magnetic and structural properties of MnRh thin films

A systematic study of magnetic and structural properties of MnRh thin films fabricated onto MgO substrates and amorphous SiO2 has been conducted. All the MnRh thin films thus fabricated are found to be of the CsCl type structure, and exhibit the ferromagnetism at room temperature. The coercivity of about 1.1 kOe was observed at 5 K for films grown onto SiO2 substrates, while coercivity measured at 300 K in all the films were less than 200 Oe. The temperature dependence of magnetization shows thermal hysteresis for all the samples ranging from 150 K to 250 K that varies with the substrates used. The maximum of exchange bias field of 270 Oe and unidirectional magnetic anisotropy constant of 0.35 erg/cm2 at 5K was observed for films grown onto SiO2 substrates better than that observed for the films grown onto MgO substrates. This enhanced exchange bias and unidirectional magnetic anisotropy constant in film grown onto SiO2 is attributed to the strong lattice distortion in such a case.

Alloy Constitution and Phase Equilibria in the Hf–Ru–Rh System. II. Liquidus Surface, Melting Diagram, and Vertical Sections of the Partial Hf–HfRu–HfRh System

According to the constitution of the solidus surface in the Hf–Ru–Rh system over the composition range 50−100 at.% Hf and the data obtained in studying the as-cast alloys by physicochemical analysis techniques, we constructed, for the first time, the liquidus surface of the partial Hf–HfRu–HfRh system on the composition triangle and its melting diagram. The vertical sections at 5 at.% Ru, 10 at.% Rh, and 75 and 80 at.% Hf at the ratio Ru : Rh = 1 : 1 are presented. The processes that occur when the alloys are crystallized are shown in the reaction scheme. The primary crystallization regions for a continuous series of solid solutions between isostructural (CsCl type) phases formed by the HfRu compound and its high-temperature modification (δ phase) as well as β-Hf and γ-Hf2Rh (Ti2Ni type) solid solutions are parts of the liquidus surface. An invariant four-phase equilibrium involving liquid, LU + δ ⇆ γ + , is observed at 1373°C in the system.

Pd–In intermetallic alloy nanoparticles: highly selective ethane dehydrogenation catalysts

2 nm PdIn intermetallic alloy (cubic, CsCl type) nanoparticle catalyst was near 100% selective to ethane dehydrogenation at 600 °C (at 15% conversion) with a dehydrogenation TOR almost 10 times higher than that of monometallic Pd.

Investigation of high pressure phase transition and electronic properties of Lutetium Nitride

In the present manuscript we have investigated the structural, electronic and phase transition properties of the heaviest lanthanide lutetium nitride (LuN) compound using an ab initio calculations based on the density functional theory with Perdrew, Burke and Ernzerhof generalized gradient approximation (PBE-GGA) and Engel-Vosko(EV)-GGA as implemented in WIEN2k code. The basic ground state properties viz., lattice constants (a), bulk modulus (B0) and its pressure derivative (B0’) and total energy (E0) are calculated. The calculated values of lattice constant is 4.76 Å which is in good agreement with experimental value a= 4.76 A and other theoretical value. The relative stabilities of LuN at high pressures in the NaCl (B1), CsCl (B2), zinc blende (B3) and body centred tetragonal (BCT) structures are analysed. At compressed volumes, this compound is found to favour the CsCl phase rather the body centred tetragonal phase and zinc blende as observed in other lanthanum pnictides, which has been predicted by the total energy minimization. Under compression LuN undergoes a transition from NaCl to CsCl type structure at around 250.81 GPa with a volume collapse of 3.75%. To see the effect of functional we have also computed the band structure in B1 and B2 structure. Obtained result on band structure shows that LuN are semimetal by GGA while depicts semiconducting behaviour by EV-GGA. It shows metallic nature in B2 phase.

The atomic structure of low-index surfaces of the intermetallic compound InPd.

The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and "global" measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature.

Prediction of new high pressure structural sequence in thorium carbide: A first principles study

In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280 (1975)].

Unbiased crystal structure prediction of NiSi under high pressure

On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is the Pmmn structure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure with a = 2.174 Å and c = 2.69 Å at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: the Pmmn structure below 213 GPa, the tetragonal CsCl type in the range 213–522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe–Ni isomorphic miscibility in FeSi.

Effects of Co introduction on hydrogen storage properties of Ti–Fe–Mn alloys

TiFe0.86Mn0.1−xCox (x = 0, 0.04, 0.05, 0.06) alloys were prepared by RF magnetic levitation melting. These alloys are determined as a single CsCl type phase. As x increases from 0 to 0.06, the unit cell volume decreases while the maximum hydrogen capacity rises to a threshold and starts to reduce thereafter. The particle size test shows that the pulverization resistance of the alloys improves significantly with the introduction of Co. After that, the effects of further increasing of Co content in this series of alloys were investigated. It is found that the appropriate proportion of Mn and Co leads to a fairly flat β phase dehydrogenation plateau. In addition, all the alloys could be easily activated. Among these alloys, TiFe0.86Mn0.05Co0.05 exhibits the highest hydrogen storage capacity of 1.98 wt.% at the temperature of 273 K, while TiFe0.86Mn0.04Co0.1 presents the best plateau property.

Structural analysis and valence variation in ytterbium pnictides YbX (X=P, As) under high pressure

We have studied the pressure induced structural phase transition, pressure volume relationship and valence variation in ytterbium pnictide compounds (YbX; X=P, As). An improved interaction potential model (IIPM) (including the polarizability effect) has been applied. We have also studied the trivalent and intermediate valence in ytterbium compounds and predicted the phase transition pressures, volume collapses for two different valences. The variations of the second-order elastic constants with pressure and stability condition have shown systematic trends in YbX compounds similar to those observed in other compounds of NaCl structure. The pressure volume relationship curves show that ytterbium pnictide compounds undergo NaCl to CsCl type structural transition. The present study also confirms that these compounds behave similar to the rare earth cerium pnictide compounds and they are trivalent in nature.

Structural, elastic, and lattice dynamic stability of yttrium selenide (YSe) under pressure: A first principle study

Structural, elastic, and lattice dynamical stability of YSe has been investigated as a function of pressure through first principles electronic band structure calculations. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of pressure suggests that the B1 phase will transform to B2 structure at ∼32 (30 GPa at 300 K obtained from comparison of Gibbs free energy at 300 K). The transition is identified to be of first order in nature with a volume discontinuity of ∼6.2% at the transition pressure. Furthermore, the theoretically determined equation of state has been utilized to derive various physical quantities, such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus. The single crystal elastic constants have been predicted at various pressures for both the B1 and B2 structures using the energy strain method. The activation barrier between B1 and B2 phases calculated at transition point is ∼19.7mRy/formula unit. Our lattice dynamic calculations show that both the B1 as well as B2 structures are lattice dynamically stable not only at ambient pressure but also at transition pressure. The B1 phase becomes lattice dynamically unstable at ∼112 GPa, i.e., much beyond the transition pressure. The effect of temperature on volume and bulk modulus of the YSe in B1 phase has also been examined.

Structural and elastic properties of ZrN and HfN: ab initio study

The present paper discusses the density functional theory based stability analysis of zirconium nitride and hafnium nitride in its rocksalt (B1), CsCl (B2), and zinc blende (B3) type phases. The ground state total energy calculation approach of the system has been used through the generalized gradient approximation parameterized with revised Perdew–Burke–Ernzerhof as exchange correlation functional. The present theoretical analysis confirms the stability trend of phases from most stable to less stable as B1 → B2 → B3. The study also reports the analysis of elastic properties of these nitrides in its most stable B1-type phase.

Structural phase transition of refractory metal carbides at high pressure

There has been significant concern in analyzing the structural stability, structural properties, and pressure-induced structural phase transition of refractory metal carbides, RC (R = Ti, Zr, Hf, V, Nb, and Ta), by using the three-body force potential model calculation modified approach. The more accurate description of the interionic spacing (r0) suggests that the interactions considered in the present computation are capable of correctly predicting the structural properties of these materials. In the preset paper, we have investigated the relative stability of the two competitive phases of metal carbides and discussed the possible phase transitions from its parental NaCl (B1) type phase to its most stable CsCl (B2) type phase in the pressure range 344–572 GPa. The computed interionic spacing (r0) and phase transition pressures (PT) are in reasonable agreement with the other reported data.

Pressure effect on elastic, lattice dynamic and superconducting behaviour of yttrium sulfide: A first principle study

First principles calculations have been carried out to analyze structural, elastic, and dynamic stability of yttrium sulphide (YS) under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of compression suggests the B1 → B2 transition at ∼49 GPa (the same transition occurs at ∼48 GPa at 300 K). Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state. The single crystal elastic constants derived from the energy strain method agree well with the experimental values. The activation barrier between B1 and B2 phases calculated at transition point is ∼17/mRy/f.u. Our lattice dynamic calculations show that at ambient condition, the B1 phase is lattice dynamically stable, and frequencies of phonon modes in different high symmetry directions of Brillouin zone agrees well with experimental values. The B2 phase also is dynamical stable at ambient condition as well as at ∼49 GPa, supporting our static lattice calculation. The effect of temperature on volume and bulk modulus of the YS in B1 phase has also been examined. The superconducting temperature of ∼2.78 K determine at zero pressure agrees well with experimental data. The effect of pressure is found to suppress the superconducting nature of this material.

Prediction of structure candidates for zinc oxide as a function of pressure and investigation of their electronic properties

In order to gain new insight in the ZnO system, we performed crystal structure prediction using simulated annealing with an empirical potential and local optimization on ab initio level, both at standard and elevated pressure. We have found the experimentally observed structure types [wurtzite (B4), sphalerite (B3), and rock salt (B1)] in agreement with previous research. In addition, many new interesting modifications were found in different regions of the energy landscape, such as the \ensuremath{\beta}-BeO type, the GeP type, the NiAs type, and the so-called ``5-5'' type modification. At extreme conditions (>150 GPa), we observe a CsCl (B2) type of structure, and as a possible intermediate phase along the NaCl (B1) \ensuremath{\rightarrow} CsCl (B2) transition route, we suggest the \ensuremath{\alpha}-WC $({B}_{h})$ modification. Furthermore, we have investigated the electronic properties of ZnO structures. Our investigations offer new possibilities of tuning the band gap with pure zinc oxide by employing modifications with different structural arrangements.

New compounds with Nd11Pd4In9 structure type in the systems RE–Pd–In (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy)

RE11Pd4In9 compounds (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy) were synthesized by arc-melting of pure metals under an argon atmosphere with subsequent annealing at 870 K and characterized by X-ray powder diffraction. They belong to the Nd11Pd4In9 structure type (space group Cmmm, Z = 2) with the following lattice constants: a = 15.581(5), b = 22.606(8), c = 3.767(1) Å for La11Pd4In9; a = 15.431(6), b = 22.516(9), c = 3.763(2) Å for Ce11Pd4In9; a = 14.883(3), b = 22.319(4), c = 3.736(1) Å for Pr11Pd4In9; a = 14.825(6), b = 22.269(8), c = 3.779(1) Å for Nd11Pd4In9; a = 14.706(2), b = 22.094(3), c = 3.729(1) Å for Sm11Pd4In9; a = 14.701(3), b = 22.046(5), c = 3.722(8) Å for Gd11Pd4In9; a = 14.614(5), b = 21.985(3), c = 3.679(2) Å for Tb11Pd4In9, a = 14.606(4), b = 21.896(6), c = 3.626(9) Å for Dy11Pd4In9. The structure is a member of the homological series REm+nM2nXm based on AlB2 (m) and CsCl (n) types.

Chemical Bonding in Zinc‐based Intermetallic Compounds with the CuTi or the CsCl Type of Structure

AbstractThe chemical bonding in the intermetallic compounds ZnPd and ZnPt with the tetragonal CuTi type of structure, and in the chemically related intermetallic compounds ZnNi, ZnCu, ZnAg, and ZnAu with the cubic CsCl type of structure, is examined applying the electron localizability approach. The analysis of the chemical bonding reveals charge transfer from zinc to the transition metal (TM), in line with the respective electronegativities. While in ZnNi, ZnCu, and ZnAg as well as ZnPd and ZnPt the Zn–TM interactions are described by multi‐center bonding and ionic interactions, mainly ionic interactions are found in the intermetallic compound ZnAu. Going from ZnNi over ZnPd to ZnPt, a gradual change from isotropic to more and more anisotropic distribution of the atomic interactions is detected, resulting in a more pronounced tetragonal distortion.

Elastic and thermodynamic properties of vanadium nitride under pressure and the effect of metallic bonding on its hardness

By the particle-swarm optimization method, it is predicted that tetragonal P42mc, I41md, and orthorhombic Amm2 phases of vanadium nitride (VN) are energetically more stable than NaCl-type structure at 0 K. The enthalpies of the predicted three new VN phases, along with WC, NaCl, AsNi, CsCl type structures, are calculated each as a function of pressure. It is found that VN exhibits the WC-to-CsCl type phase transition at 256 GPa. For the considered seven crystallographic VN phases, the structures, elastic constants, bulk moduli, shear moduli, and Debye temperatures are investigated. Our calculated equilibrium structural parameters are in very good agreement with the available experimental results and the previous theoretical results for the NaCl phase. The Debye temperatures of VN predicted three novel phases, which are all higher than those of the remaining structures. The elastic constants, thermodynamic properties, and elastic anisotropies of VN under pressure are obtained and the mechanical stabilities are analyzed in detail based on the mechanical stability criteria. Moreover, the effect of metallic bonding on the hardness of VN is also investigated, which shows that VNs in P42mc, I41md, and Amm2 phases are potential superhard phases. Further investigation on the experimental level is highly recommended to confirm our calculations presented in this paper.