Pseudobinary Compounds Research Articles

ChemInform Abstract: Stabilization by Si Substitution of the Pseudobinary Compound Gd2(Co3‐xSix) with Magnetocaloric Properties Around Room Temperature.

AbstractThe new solid solution Gd2(Co3‐xSix) (0.29 < x < 0.50) is obtained by arc‐melting of the elements.

Experimental Study of the Magnetocaloric Effect in the Pseudo Binary Laves-Phase Compounds

Polycrystalline samples of DyCo 2, HoCo 2, ErCo 2 and their solid solutions Dy1-xHoxCo2, Dy1-xErxCo2, Ho1-xErxCo2 have been studied using X-ray diffraction analysis, heat capacity and magnetic measurements. The X-ray diffraction performed at room temperature allowed to reveal that all solid solutions solidify with the formation of the C15 cubic Laves-phase structure corresponding to the Fd3m space group. All binary compounds and their solid solutions are typical ferrimagnets and are magnetically ordered at temperature below 140 K. In all doped solid solutions an decrease of the magnetic ordering temperature is observed. At high temperatures, all samples are Curie-Weiss paramagnets. The magnetization behaviour and the magnetic transition are analyzed in terms of Landau theory. The magnetocaloric effect has been estimated using the heat capacity data.Comparison of the influence of doping effect in pseudo-binary compounds on their magnetic and magnetocaloric properties for all solid solutions is presented.

Stabilization by Si Substitution of the Pseudobinary Compound Gd2(Co3–xSix) with Magnetocaloric Properties around Room Temperature

We report the discovery of a new solid solution Gd2(Co3-xSix) with 0.29 < x < 0.50 in the Gd-Co-Si ternary system. Members of this solid solution crystallize with the La2Ni3-type structure and correspond to the stabilization of "Gd2Co3" through silicon substitution. The structure of the member Gd2(Co2.53(3)Si0.47) was determined by X-ray diffraction on a single crystal. It crystallizes with the space group Cmce and cell parameters a = 5.3833(4), b = 9.5535(6), and c = 7.1233(5) Å. Co/Si mixing is observed on two crystallographic positions. All compounds studied in the solid solution present a ferrimagnetic order with a strong composition-dependent Curie temperature TC with 280 K < TC < 338 K. The magnetocaloric effect, which amounts to around 1.7 J K(-1) kg(-1) for ΔH = 2 T, is interestingly tunable around room temperature over a temperature span of 60 K through only 4-5% of composition change.

Structural and optical properties of (Ag,Cu)(In,Ga)Se2 polycrystalline thin film alloys

The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se2 polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined ao lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined co lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derived from transmission and reflection measurements, widened with increasing Ag and Ga content, due to influences from anion displacement and cation electronegativity, as expected from theoretical considerations for pseudo-binary chalcopyrite compounds.

Ti(Ni,Cu) pseudobinary compounds as efficient negative electrodes for Ni–MH batteries

The effect of Ni by Cu substitution on the structural, solid–gas and electrochemical hydrogenation properties of TiNi has been investigated. Pseudo-binary TiNi1−xCux (x ≤ 0.5) compounds have been synthesized by induction melting. They crystallize in B2 structure above 350 K and either in B19′ (x < 0.1) or B19 (0.2 ≤ x ≤ 0.5) at room temperature (RT). For all compounds, Pressure-Composition Isotherms at 423 K exhibit a single slopping plateau pressure within the range 10−3–1 MPa of hydrogen pressure revealing a metal to hydride transformation. Both the hydrogenation capacity and the hydride stability decrease with Cu-content. The hydrided pseudobinary compounds crystallize in the tetragonal S.G. I4/mmm structure as for TiNi hydride. The electrochemical discharge capacity increases with Cu content from 150 mAh g−1 for TiNi up to 300 mAh g−1 for TiNi0.8Cu0.2 and then decreases again for larger Cu amounts. Electrochemical isotherms and in-situ neutron diffraction measurements at RT demonstrate that such a capacity increase results from a metal to hydride phase transformation in which the hydride phase is destabilized by Cu substitution. The TiNi0.8Cu0.2 compound exhibits interesting cycling stability for 30 cycles and good high-rate capability at D/2 rate. This compound has promising electrochemical properties as compared to commercial LaNi5-type alloys with the advantage of being rare-earth metal free.

The Structural, Electrical And Magnetic Properties Of Perovskite (1-x)Ba(Fe1/2Nb1/2)O3–xBaTiO3 Ceramics

Lead-free pseudo-binary compounds (1-x)Ba(Fe1/2Nb1/2)O3–xBaTiO3; (0 ≤ x ≤ 1) have been synthesized at 1200°C using conventional ceramic technique and characterized by X-ray diffraction, scanning electron microscopy, dielectric and vibration sample magnetometer studies. The crystal structure of the compounds is found to be monoclinic with the space group P2/m except for BaTiO3 for which it is tetragonal (P4/mmm). The incorporation of BaTiO3 significantly reduces the dielectric loss and improve the frequency and temperature stability of the dielectric properties of Ba(Fe1/2Nb1/2)O3. Compound 0.25Ba(Fe1/2Nb1/2)O3-0.75BaTiO3 exhibited a low value of temperature coefficient of capacitance (< ±3%) in the working temperature range (up to +85°C), room temperature dielectric constant equal to 282 and low loss tangent (~10-2) which meets the specifications for “Z5D” of Class II dielectrics of Electronic Industries Association. Hence, this composition might be a suitable candidate for capacitor applications. Besides, magnetic studies indicated the possibility of magneto-electric coupling in the system.

Hydrogen Storage in Martensite Ti–Zr–Ni Alloy: A Density Functional Theory Study

The hydrogen storage potential of TiNi-based shape memory alloys is an attractive but experimentally challenging issue. We employ the FP (L)APW+lo method, based on the density functional theory (DFT), in order to address the electronic structure of the low-temperature, martensitic phase of Ti0.67Zr0.33Ni and its hydrides. Further, the thermodynamics of hydride formation in the martensitic Ti–Zr–Ni alloys is studied, and some unanswered questions regarding the hydriding of martensite TiNi are resolved. The calculated formation energy of the orthorhombic β- and γ-hydrides of martensitic Ti0.67Zr0.33Ni is, respectively, −14.2 kJ/mol(H) and −29.6 kJ/mol(H), showing that isostructural (Ti,Zr)Ni hydrides with a larger amount of titanium have improved potential for hydrogen storage applications. Furthermore, based on the calculation results, it is unlikely that the hydriding of TiNi martensite would lead to the formation of orthorhombic β-hydride in analogy to the pseudobinary compound. The formation of Ti0.67Zr...

Effect on Magnetic Properties of Al Atoms in YFe2 and YCo2

From the theoretical point of view, magnetic properties of pseudo-binary compounds Y(Fe, Al)2 and Y(Co, Al)2 with the cubic Laves phase structure are reviewed. Assuming an ordered atomic structure, the electronic structures in these compounds are calculated in the self-consistent augmented-plane-wave (APW) method, and the effect of the Al atoms on the magnetic properties is discussed.

Structural, electrical and optical study of thermally evaporated Ge8Sb2Te11 thin films

Thin films of GeTe-rich pseudobinary compound, Ge8Sb2Te11, have been synthesized from its polycrystalline bulk by thermal evaporation. Amorphous nature of thermally evaporated films has been confirmed by X-ray diffraction study. The temperature dependent electrical, optical and structural properties are presented. For films annealed at 190°C, a large change in electrical and phase transition temperature was observed, with almost no change in optical properties. The phase transition temperature of Ge8Sb2Te11 was ~205°C and decreases appreciably for the post deposition films annealed at 190°C. The films morphology and their chemical composition have been studied using Scanning electron microscopy linked with energy dispersive X-ray spectrometer.

Phase relationships and crystal structure in the pseudobinary system La5Si4–La5Ge4

Phase relationships and crystal structures at room temperature in the pseudobinary system La5Si4–La5Ge4 were investigated by X-ray powder diffraction. Two structurally distinct single phase regions were found in this system. The Si-rich La5Si4−xGex pseudobinary compounds with 0⩽x⩽2.9 crystallizes in Zr5Si4-type tetragonal structure with space group P41212. The Ge-rich pseudobinary compounds with 3.1⩽x⩽4.0, adopt a Sm5Ge4-type orthorhombic structure with space group Pnma. The lattice parameters and atomic coordinates were derived using the Rietveld refinement method. The Wigner–Seitz cell volume (WSV) calculations indicate that the values of WSV for La atoms at different sites are sensitive to the crystal structure and Ge concentration, which is related to the structural transition induced by composition in La5Si4–La5Ge4system.

Pressure Dependent Magnetism in Y1.05(Mn0.95Al0.05)2

The Laves phase compound YMn2 exhibits a discontinuous transition from a spin fluctuating Pauli paramagnetic state above 110 K to an expanded, localised moment helical antiferromagnetic state below 110 K. Substitution of Al for Mn in the pseudo-binary compound Y(Mn1-xAlx)2 exerts a negative chemical pressure, expanding the unit cell and further localizing the Mn moment. Here we present the results of a μSR study of spin fluctuations in Y(Mn1-xAlx)2 (x = 0.05) in which external mechanical pressure (4.5 kbar) is applied to counteract the Al induced chemical pressure and destabilize the local Mn moment.

A structural study of Cu–In–Se compounds by x-ray absorption fine structure

Abstract

Magnetic properties and magneto-caloric effect in pseudo-binary intermetallic (Ce,R) 2Fe 17 compounds (R = Y, Pr and Dy)

We have synthesized three pseudo-binary (Ce,R) 2Fe 17 intermetallic alloys, where cerium has been partially substituted by R = Y, Pr and Dy, with the aim of tuning the Curie temperature (between 253 and 273 K) for obtaining the maximum magneto-caloric response of the alloys just below room temperature. The analysis of the x-ray powder diffraction patterns show that the three samples crystallize in the rhombohedral Th 2Zn 17-type crystal structure (space group R 3 ¯ m ). We report the temperature dependence of the isothermal magnetic entropy change, |Δ S M |( T), the magnetic field dependence of its maximum value, |Δ S M ma x|( H), and the relative cooling power around the second-order magnetic transition for magnetic field changes μ 0Δ H max = 5 T. The collapse of the normalized Δ S M ( θ)/Δ S M max vs. temperature (where θ is a rescaled temperature) into a single master curve allows the extrapolation of |Δ S M |( T) curves for higher magnetic field changes, and/or the estimation of the temperature dependence of the magnetic entropy for other 2:17 pseudo-binary compounds. The lower values of |Δ S M ma x| compared with those of the R 2Fe 17 compounds with R = Pr or Nd are explained in terms of the decrease of the saturation magnetization. The magnetic field dependence of the |Δ S M ma x| indicates that only Pr 1.5Ce 0.5Fe 17 alloy roughly follows a mean-field behaviour.

Modeling of thermodynamic properties of ABr–PrBr 3 (A=Li–Cs ) systems

The thermodynamic properties of ABr–PrBr 3(A=Li–Cs) systems were assessed by the CALPHAD method. The liquid phase in the systems was described by the non-stoichiometric associate model. The entropies of mixing in the liquid were evaluated from experimental liquidus and enthalpy of mixing data. For the pseudobinary compounds A 3PrBr 6,APr 2Br 7, and A 2PrBr 5 (A=K,Rb) and Cs 3PrBr 6 and CsPr 2Br 7, the dependences of Gibbs energies of formation on temperature were calculated. The anomalies of sequences of thermodynamic properties in RbBr–PrBr 3 were observed and discussed. The nature of the liquid phase and precision of calculations of the Rb 2PrBr 5(s) compound were discussed.

Effect of Lead Oxide Vapor on the Strength of Alumina

This effect of PbO vapor on the strength of alumina was studied to determine the corrosion mechanism. Characterization of the corroded samples was carried out using X-ray diffraction (XRD), scanning electron microscopy, strength and sound velocity measurements, weight and dimensional changes. The strength and sound velocity of alumina decreased when exposed to PbO but weight and volume increased. Thermodynamic modeling of the PbO–Al2O3 system was carried out using the CALculation of PHAse Diagram method, which showed that three pseudo-binary compounds, PbAl2O4, Pb2Al2O5, and PbAl12O19 can be formed, in agreement with prior work. It was postulated that PbAl12O19 is most likely to form when alumina is exposed to PbO at sintering temperatures and this was confirmed by XRD and energy-dispersive analysis. The PbAl12O19 phase does not form a surface layer but rather nucleates and grows as individual crystals embedded in the alumina surface, forming a more porous structure. This surface porosity then acts to concentrate applied stress, resulting in a lower strength. This strength degradation mechanism makes alumina kiln furniture more sensitive to thermal stresses with repeated use, explaining the observed cracking behavior.

Hydrogenation properties of shape memory Ti(Ni,Pd) compounds

The effect of Pd substitution on the crystal structure and hydrogenation properties of TiNi compound has been investigated. Ti(Ni,Pd) are pseudo-binary compounds. The unit-cell volumes of B2 (Austenite) and B19 (Martensite) structures linearly increase with Pd substitution in Ti 1.04Ni 0.96− x Pd x samples. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are not affected by the crystal structure of the parent compounds. For all samples, hydrogen absorption occurs without showing any clear plateau pressure in Pressure-Composition-Isotherm (PCI) curves. All hydrided samples crystallise in the tetragonal I 4/ mmm space group. At 6 MPa of hydrogen pressure and T = 423 K, the hydrogenation capacity of Ti(Ni,Pd) compounds reaches 1.52 hydrogen atoms per formula unit (H/f.u.) for x = 0.1 and then gradually decreases with Pd content down to 0.93 H/f.u. for x = 0.5. Ti 1.04Ni 0.86Pd 0.10 sample yields a discharge capacity of 148 mAh/g at C/5 regime when used as negative electrode in Ni-MH battery. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are discussed in detail by comparison with previous studies on Zr substituting, (Ti,Zr)Ni compounds.

Synthesis, properties and Mössbauer study of ZrFe 2− xNi x hydrides ( x = 0.2–0.8)

Interaction of ZrFe 2− x Ni x ( x = 0.2, 0.4, 0.6, and 0.8) pseudobinary intermetallic compounds with hydrogen was studied. It was found that these compounds can accumulate up to 1.7–1.8 wt.% H 2 at room temperature. For all investigated ZrFe 2− x Ni x –H 2 systems, thermodynamic functions of the β-hydride → α-solution phase transition and changes of metal matrix volume during formation of hydrides were calculated. It was shown that increase in Ni content leads to reduction of both desorption pressures and starting pressures of reaction with hydrogen in the first hydrogenation cycle compared to ZrFe 2. Mössbauer investigations, which have been carried out for all alloys as well as hydrides, revealed that Curie temperatures ( T c) and average hyperfine fields (HF av) of initial alloys decrease with Ni content increase, while isomer shifts (IS) remain constant. Absorption of H 2 results in significant increase in IS together with some increase in T c and HF av for all samples. The decomposition of the hydride phases to intermetallic phases while heating from 78 K to room temperature was found to be a two-step process involving formation of the hydride phases with intermediate hydrogen content.

Isothermal section of the Al–Dy–Ge ternary system at 673 K

The isothermal section of the phase diagram of the Al–Dy–Ge ternary system at 673 K has been investigated by X-ray powder diffraction and scanning electron microscope equipped with energy dispersive X-ray spectroscopy in backscattered electron imaging modes. The existence of thirteen binary compounds including Dy 3Ge 4 in the system Dy–Ge has been confirmed. Four ternary compounds, namely AlDyGe, Al 3Dy 2Ge 4, AlDy 2Ge 3, and AlDy 2Ge 2 were observed, and five new ternary compounds, i.e., Al 0.33DyGe 2, AlDy 2Ge 6, Al 2DyGe 2, AlDy 3Ge 3, and Al 3− x Dy 11Ge 7+ x ( x ≤ 0.7), and one pseudo-binary compound Al 3− x DyGe x were found in this system at 673 K. The maximum solid solubility of Ge in the pseudo-binary compounds Al 3− x DyGe x is about 7.5 at.% with x = 0.3 at 673 K.

Investigation on the magnetocaloric effect in (Gd,Pr)Al2 solid solutions

A theoretical and experimental investigation on the magnetocaloric properties of the rare earth pseudo-binary compounds Gd1−nPrnAl2 is presented. The calculated isothermal entropy and adiabatic temperature changes under magnetic field variations from 0 to 2T and from 0 to 5T are in good agreement with the experimental data. For the Pr-concentrations n=0.25, 0.5 and 0.75 the experimental data present an inverse magnetocaloric effect which was theoretically predicted and associated with the competition between the opposite magnetizations of the Gd and Pr sublattices. The two-sublattice Hamiltonian used in the calculations takes into account the crystal field, exchange and Zeeman interactions.

Structural investigation of GeSb6Te10 and GeBi6Te10 intermetallic compounds in the chalcogenide homologous series

The crystal structures of GeSb(6)Te(10) and GeBi(6)Te(10) were scrutinized using an X-ray powder diffraction method, which revealed that these compounds crystallize in trigonally distorted cubic close-packed structures with a 51-layer period (R3m). Each layer consists of a triangular atomic net; Te atoms occupy their own specific layers, whereas Ge, Sb and Bi atoms are located in the other layers. In these pseudobinary compounds, random atomic occupations of Ge and Sb/Bi are observed and the layers form two kinds of elemental structural blocks by their successive stacking along the c axis. These compounds can be presumed to be isostructural. It is known that the chemical formula of the chalcogenide compounds with the homologous structures found in these pseudobinary systems can be written as (GeTe)(n)(Sb(2)Te(3))(m) or (GeTe)(n)(Bi(2)Te(3))(m) (n, m: integer); the GeSb(6)Te(10) and GeBi(6)Te(10) investigated in this study, which correspond to the case in which n = 1 and m = 3, naturally have 3 x l = 51-layer structures according to a formation rule l = 2n + 5m commonly found in the compounds of these chalcogenide systems (l represents the number of layers in the basic structural unit). Calculations based on the density functional theory revealed that these materials are compound semiconductors with very narrow band gaps.