Cd Alloy Research Articles

Ternary alloys Cd y Zn1 − y O and Mg x Zn1 − x O as materials for optoelectronics

Thin films of Cd y Zn1 − y O and Mg x Zn1 − x O (y = 0−0.35, x = 0−0.45) ternary alloys have been grown by pulsed laser deposition onto sapphire substrates. The record solubility limits of Cd (y = 0.3) and Mg (x = 0.35) have been achieved in hexagonal zinc oxide. The mismatch of the lattice parameters a of Cd0.2Zn0.8O and Mg0.35Zn0.65O does not exceed 1%; in this case, the band gap discontinuity is 1.3 eV. The surface roughness of the films does not exceed 2.5 nm at x = 0−0.27 and y = 0−0.20.

Phase identification in electrodeposited Ag–Cd alloys by anodic linear sweep voltammetry and X-ray diffraction techniques

During electrodeposition of Ag–Cd alloy coatings phenomena of self-organization and formation of spatio-temporal structures can be observed. The difficulties in the determination of the local phase composition in the observed structures are mostly connected with the strong heterogeneity of the coatings consisting of several alloy phases. The results obtained with electrochemical techniques, such as anodic linear sweep voltammetry (ALSV) are compared with results obtained by X-ray analysis and SEM. In the proposed electrolyte for dissolution of Ag–Cd alloy coatings (12 M LiCl + 0.1 M HCl) the dissolution peaks of the pure metals, Ag and Cd, have a potential difference of about 700 mV. The peaks, corresponding to the alloy phases, are situated between the dissolution potentials of Ag and Cd, their height depending on the deposition current density, i.e. on the percentage content of the alloy. Different phases (Ag, Ag 3Cd, AgCd, AgCd 3 and pure Cd) are observed in the coatings deposited at different cathodic potentials. A good correlation between the XRD spectra of the Ag–Cd alloy coatings and the ALSV data obtained during their dissolution is established.

Interface Dipole and Schottky Barrier Formation at Au/CdZnTe(111)A Interfaces

Synchrotron radiation photoemission spectroscopy (SRPES) has been used to study the electronic structure of the Au/CdZnTe(111)A for Au coverage ranging from about 0.3 up to 20 monolayers (ML). It is found that a Schottky barrier with a height of 0.82 eV is formed at the initial deposition of Au. This barrier decreases gradually with increasing Au coverage, which can be ascribed to band bending caused by charge redistribution at the interface and the formation of a positive interface dipole introduced by Cd diffusion. After an annealing process, a signal due to the formation of Au−Cd alloy caused by exquisite Cd diffusion into Au overlayer is observed, and simultaneously the Schottky barrier height (SBH) reduces to 0.32 eV. The present work indicates that cation diffusion into metal overlayer plays a critical role in controlling the SBH.

Effect of Cd content on the kinetics of low-temperature structural transformation in In–Cd alloy

The effect of the Cd concentration on the kinetics of a spontaneous low-temperature structural phase transformation previously observed in the martensite phase of the solid solution In–Cd is investigated. Acoustic, resistive, and calorimetric measurements are performed in the temperature interval 100–340K on samples containing 4.3, 5.5, and 6.6at.% Cd. It is established that the transformation rate increases considerably with increasing Cd concentration. The empirical activation parameters of the transformation are obtained: activation energy U0=0.43eV and period of attempts τ0=5⋅10−9s. It is shown that this transformation has the characteristic features of a first-order phase transition. It is suggested that the low-temperature isothermal instability of the macroscopic properties of the alloy is due to the decomposition of the In-based solid solution. The substantial increase of the decomposition rate with increasing Cd concentration could be due to an increase of the driving force of this process.

Existence or absence of bandgap bowing in II-VI ternary alloys: Comparison between common-anion and common-cation cases

The common-anion and common-cation II-VI ternary alloys of the family Cd(Zn)Se(Te) are theoretically investigated based on two different methods. Within the virtual-crystal approximation (VCA), both the sp3s*-tight-binding method, with the inclusion of spin-orbit coupling, and the first-principle full-potential linear augmented plane waves (FP-LAPW) technique are employed to determine the alloy constituents' charge states (ionicities) and degree of bond polarity. The results show that: (i) in the common-cation ternary alloys (i.e., CdSexTe1−x and ZnSexTe1−x), the anions alter a strong competition in trapping more charge. Such a competition builds up a compromised effect yielding the bowing behaviour. Whereas, (ii) in the common-anion ternary alloys (i.e., CdyZn1−yTe and CdyZn1−ySe), the absence of such competition would cause the complete absence of bandgap bowing behaviour. The variation of the bandgap is found to be rather close to linear. The obtained good agreement between our theoretical results and the recently available photoluminescence data does further corroborate our claims.

Hydrogen Electrosorption into Pd−Cd Nanostructures

Hydrogen-absorbing materials are crucial for both the purification and storage of hydrogen. Pd and Pd-based alloys have been studied extensively for their use as both hydrogen dissociation catalysts and hydrogen selective membrane materials. It is known that incorporating metal atoms of different sizes into the Pd lattice has a major impact on the hydrogen absorption process. In this paper, hydrogen electrosorption into nanostructured Pd-Cd alloys has been studied for different compositions of Cd that varied from 0 to 15 at. %. The low cost of Cd makes it an attractive material to combine with Pd for hydrogen sorption. A combination of chronoamperometry and cyclic voltammetric experiments was used to determine the ratio of the H/(Pd + Cd) and the kinetics of hydrogen sorption into these Pd-Cd alloys at different potentials. It was found that the maximum H/(Pd + Cd) value was 0.66 for pure Pd, and this decreased with increasing the amount of Cd. Also, the alpha (solid solution) to beta phase (metal hydride) hydrogen transition was determined to be the slowest step in the absorption process and was practically eliminated when an optimum amount of Cd atoms was doped (i.e., Pd-Cd(15%)). With increasing the amount of Cd, more hydrogen was absorbed into the Pd-Cd nanostructures at the higher potentials (the alpha phase region). The faster kinetics, along with the decrease in the phase transition of hydrogen sorption into the Pd-Cd nanostructures when compared to pure Pd, makes the Pd-Cd nanostructures attractive for use as a hydrogen dissociation catalytic capping layer for other metal hydrides or as a hydrogen selective membrane.

Effect of Exciton-Longitudinal Optical Phonon Interaction on Exciton Binding Energies in CdxZn1-xS/ZnS Single Quantum Wells

We study the effect of the exciton-longitudinal optical (LO) phonon interaction on the exciton binding energies in CdxZn1-xS/ZnS single quantum wells (SQWs) for the Cd alloy content (x) range 0.1—0.3. The heavy- and light-hole exciton binding energies increase with the exciton-LO phonon interaction. The increase in the maximum heavy-hole (light-hole) exciton binding energy for x = 0.3 is 9.1 meV (4.9 meV). In narrow CdxZn1-xS/ZnS SQWs, the heavy-hole exciton binding energy calculated by taking into account the exciton-LO phonon interaction for values of x in the range 0.1—0.3 exceed the LO phonon energy of CdxZn1-xS. [DOI: 10.1380/ejssnt.2010.340]

Study on low activation decoupler material for MW-class spallation neutron sources

The Japan Spallation Neutron Source (JSNS) at the Japan Proton Accelerator Research Complex (J-PARC) has started its operation on May 30, 2008. The Ag–In–Cd (AIC) alloy was adopted as a decoupler material for two decoupled moderators. A high decoupling energy at 1 eV was for the first time achieved in MW-class spallation neutron sources due to the adoption of the AIC alloy. Although the AIC decoupler is superior in the neutronic performance, it has a demerit in high residual radioactivity due to production of Ag-110 m (half life: 250 days) and Ag-108 m (half life: 418 years). To overcome this demerit, we studied on possibilities of a low activation decoupler material with high decoupling energy as the AIC alloy, that is, Au–In–Cd (AuIC) alloy. Neutronic performance of this material was investigated by using neutronics calculations. As a result, it was found that the AuIC decoupler could provide neutron pulses with almost the same characteristics as those for the AIC decoupler even when the burn-up effects were considered. Excellent low activation property of the AuIC alloy to the AIC alloy was demonstrated by residual radioactivity calculations. On viewpoint of neutronics performance, it was concluded that the AuIC decoupler was available as the substitute of the AIC decoupler.

Alloy formation during the electrochemical growth of a Ag–Cd ultrathin film on Au(1 1 1)

The electrodeposition of a Ag/Cd ultrathin film on a Au(1 1 1) surface and the formation of a surface alloy during this process have been studied using classical electrochemical techniques and in situ Scanning Tunneling Microscopy (STM). The films were obtained from separate electrolytes containing Ag + or Cd 2+ ions and from a multicomponent solution containing both ions. First, the polarization conditions were adjusted in order to form a Ag film by overpotential deposition. Afterwards, a Cd monolayer was formed onto this Au(1 1 1)/Ag modified surface by underpotential deposition. The voltammetric behavior of the Cd UPD and the in situ STM images indicated that the ultrathin Ag films were uniformly deposited and epitaxially oriented with respect to the Au(1 1 1) surface. Long time polarization experiments showed that a significant Ag–Cd surface alloying accompanied the formation of the Cd monolayer on the Au(1 1 1)/Ag modified surface, independent of the Ag film thickness. In the case of an extremely thin Ag layer (1 Ag ML) the STM images and long time polarization experiments revealed a solid state diffusion process of Cd, Ag, and Au atoms which can be responsible for the formation of different Ag–Cd or Au–Ag–Cd alloy phases.

An effective interaction potential model for the shape memory alloy AuCd

The unusual properties of shape memory alloys (SMAs) result from a lattice level martensitic transformation (MT) corresponding to an instability of the SMAs crystal structure. Currently, there exists a shortage of material models that can capture the details of lattice level MTs occurring in SMAs and that can be used for efficient computational investigations of the interaction between MTs and larger-scale features found in typical materials. These larger-scale features could include precipitates, dislocation networks, voids, and even cracks. In this article, one such model is developed for the SMA AuCd. The model is based on effective interaction potentials (EIPs). These are atomic interaction potentials that are explicit functions of temperature. In particular, the Morse pair potential is used and its adjustable coefficients are taken to be temperature dependent. An extensive exploration of the Morse pair potential is performed to identify an appropriate functional form for the temperature dependence of the potential parameters. A fitting procedure is developed for the EIPs that matches, at suitable temperatures, the stress-free equilibrium lattice parameters, instantaneous bulk moduli, cohesive energies, thermal expansion coefficients, and heat capacities of FCC Au, HCP Cd, and the B2 cubic austenite phase of the Au-47.5at%Cd alloy. The resulting model is explored using branch-following and bifurcation techniques. A hysteretic temperature-induced MT between the B2 cubic and B19 orthorhombic crystal structures is predicted. This is the behavior that is observed in the real material. In addition to reproducing the important properties mentioned above, the model predicts, to reasonable accuracy, the transformation strain tensor and captures the latent heat and thermal hysteresis to within an order of magnitude.

Defects and Diffusion in a Prototype of Shape Memory Alloys: β<sub>2</sub>' Au-Cd Alloys

The Au-Cd alloys continue to be important vehicles of research for the shape memory effect involving martensitic transformations and related phenomena.They transform to a variety of martensitic structures depending on the alloy composition and thermal history. Additionally, the Au-rich alloys display rubber like behavior involving thermo-elastic memory. Defects and diffusion play important roles in determining these properties. Defects and diffusion mechanisms in the Au- 47.5 - 50.5 at.% Cd alloys are examined. Diffusion in the nanometer regime and the states of defects are found to be important contributing factors to determine the shape memory effect, the variable martensitic transformations and the rubber like behavior, which are discussed in details.

Synthesis and spectroscopic study of high quality alloy Cd x Zn1−x S nanocrystals

In the present study, we report the synthesis of high quality Cd x Zn1−x S nanocrystals alloy at 150°C with changing the composition. The shifting of absorption and emission peak in shorter wavelength is obtained with increasing the mole fraction of zinc. The quantum yield (QY) value decreases with increasing the Cd mole fraction and the values are 0·08, 0·13 and 0·40 for Cd0·62Zn0·38S, Cd0·52Zn0·48S and Cd0·31Zn0·69S nanocrystals, respectively after 120 min of reaction. However, the full width at halfmaximum (fwhm) values are 45, 34 and 28 nm and the corresponding quantum yield (QY) values are 0·52, 0·17 and 0·13 for 0·5 mM, 1·5 mM and 3 mM of initial S concentrations, respectively. It is interesting to note that the radiative decay time is dominating with increasing the Cd content. Analysis suggests that the decay dynamics depends on the composition of Cd x Zn1−x S nanocrystals.

Electrical resistivity of liquid Mg–Al, Na–Cs, Ni–Ce, Li–Cd and Mg–Cd alloys within the‘2kF’ scattering model

The resistivities of liquid Mg–Al, Na–Cs, Ni–Ce, Li–Cd and Mg–Cd alloys werecalculated. The Faber–Ziman diffraction model and the Morgan–Howson–Saub‘2kF’ scattering model were used in calculations. The results obtained within these two modelsfor the same alloy and with use of the same set of parameters differ substantially, even foralloys that are not highly resistive. It is possible in principle to achieve good agreementwith experiment by means of each of these two models; however we suggest that the‘2kF’ scattering model is the appropriate method of calculation of the electrical resistivity forliquid alloys because the quantum interference effects should always be taken intoaccount.

Low Temperature Kinetics of In-Cd Solid Solution Decomposition

An influence of Cd content on the kinetics of a spontaneous low-temperature structure transformation in In-rich In - Cd alloys has been investigated using acoustic, resistivity and DSCtechniques. It is established that increase of the concentration of Cd leads to an essential increase of a driving force of the transition that results in an increase of the transition rate and in decrease of the relaxation time. The low-temperature instability of acoustic, resistivity and thermal properties is caused presumably by a decomposition of the solid solution that has features of a phase transition of the 1st order. The main empirical activation parameters of the transformation are derived. The activation energy amounts to U0 = 0.43 eV, the attempt period is τ 0 =5 × 10-9 s. The probable border of the decomposition in the phase diagram of the In-Cd system is established.

Photoluminescence study of ZnCdO alloy

The photoluminescence (PL) properties of ZnCdO alloy are investigated at various temperatures. Each PL profile contains four distinct peaks: P1, P2, P3, and P4. Peak P4 is due to free-excitonic recombination. The temperature mapping of the P3 peak position shows an S-shaped shift similar to the InGaN system due to the inhomogeneous distribution of Cd in ZnCdO alloy. The peak P2 is attributed to the phonon replica of the localized excitonic emission (P3). The linewidth of the photoluminescence profiles of the ZnCdO alloy is shown to depend on the concentration of Cd.

LIQUID FILM MIGRATION IN A Cu-2.65 at% Cd ALLOY

Liquid film migration has been studied in a Cu-2.65 at% Cd alloy in the temperature range 516 to 627 °C. The microstructure developed during migration and the migration distance was recorded as a function of time and temperature. The rate of migration of the liquid film was determined at each transformation temperature during both down-quenching and up-quenching experiments. Experiments were also carried out to determine the composition of the leading and trailing crystals across the liquid film and were used to calculate the coherency strain energy. The total chemical free energy change was calculated at each transformation temperature using the regular solution model to represent ∆G for the liquid and solid solutions.The diffusion coefficients were calculated from a number of parameters such as composition of the solid and liquid solutions, rate of migration, thickness and radius of the liquid film, modulus of elasticity, misfit parameter and the activity coefficients of the liquid and solid solutions.On a étudié la migration de film liquide d’un alliage de Cu-2.65 % atome Cd dans la gamme de température de 516 à 627 °C. On a noté la microstructure développée lors de la migration ainsi que la distance de migration en fonction du temps et de la température. On a déterminé la vitesse de migration du film liquide à chaque température de transformation lors des expériences de trempe, tant vers le bas que vers le haut. On a également effectué des expériences afin de déterminer la composition des cristaux de tête et de queue à travers le film liquide et l’on a utilisé ces dernières pour calculer l’énergie de déformation de la cohérence. On a calculé le changement total d’énergie chimique libre à chaque température de transformation en utilisant le modèle de solution régulière pour représenter ∆G pour les solutions liquides et solides.On a calculé les coefficients de diffusion à partir d’un nombre de paramètres comme la composition des solutions solides et liquides, la vitesse de migration, l’épaisseur et le rayon du film liquide, le module d’élasticité, le paramètre d’inadaptation et les coefficients d’activité des solutions liquides et solides.

New insights on the Cd UPD on Au(111)

AbstractThe Cd underpotential deposition (UPD) process on Au(111) was analyzed by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). In the underpotential range 300⩽ΔE (mV) ⩽400, 2D Cd islands are formed on the fcc regions of the Au(111)‐(√3 × 22) reconstructed surface without lifting the reconstruction. At lower underpotentials, the 2D Cd islands grow and, simultaneously, new 2D islands nucleate and coalesce with the previous ones forming a complete condensed Cd monolayer (ML). STM images and long time polarization experiments performed at ΔE = 70 mV demonstrate the formation of an AuCd surface alloy. At ΔE = 10 mV, the formation of the complete Cd ML is accompanied by a significant AuCd surface alloying and the kinetic results reveal two different solid‐state diffusion processes. The first one, with a diffusion coefficient D1 = 4 × 10−17 cm2 s−1, could be ascribed to the mutual diffusion of Au and Cd atoms through a highly distorted (vacancy‐rich) AuCd alloy layer. The second and faster diffusion process (D2 = 7 × 10−16 cm2 s−1) is associated with the appearance of an additional peak in the anodic stripping curves and could be attributed to the formation of another CdzAux alloy phase. Copyright © 2008 John Wiley & Sons, Ltd.

Peculiarities of Voltammetry and Dissociation of Hydroxycarboxylic Acids

The study of voltammetry of two hydroxycarboxylic acids: D-tartaric and citric acids at the electrodes from Pt, Cu, Ta, Cu-Hg and alloys of Cd with Sn, Ni, Hg, In in aqueous solutions shows that these acids in all cases form the hydrogen ions discharge process waves. With the aid of the suggested by authors method the values of the degrees of dissociation of various hydroxycarboxylic acids (D-, L-, DL-, meso-tartaric, citric, malic acids) in the concentration range 0.0001-0.01M and the pH range 1-4 were calculated.

The grain size dependence of flow stress in a Cu–1%Cd alloy

The dependence of flow stress on grain size was studied in a Cu–1%Cd alloy. The Hall–Petch constants are related to true strain in such a way that σ 0( ɛ) is proportional to ɛ and k( ɛ) having negative variation with ɛ 1/2. A new equation for flow stress as a function of true strain ( ɛ) and grain size ( d) has been evolved for this alloy.

Crystallography of stress-induced [formula omitted] (trigonal) martensitic transformation in Au–49.5 at.%Cd alloy

The crystallography of B 2 - ζ 2 ′ (trigonal) stress-induced transformation in Au–Cd has been controversial. The present study was undertaken to clarify this issue by obtaining reliable experimental data, which enabled a critical test for the phenomenological crystallographic theory of martensitic transformation. The results revealed that the lattice invariant shear (LIS) was {1 0 0}〈0 1 1〉 C twinning in contrast to {0 1 1}〈1 0 0〉 C twinning, which was believed to be the case by all the previous investigators. The theoretical calculations using {1 0 0}〈0 1 1〉 C twinning agreed well with the observations in all respects. Therefore, the phenomenological crystallographic theory is shown to be well applicable to the present transformation. In addition to the stress-induced transformation, the morphologies of thermally induced martensites were examined, and two types of morphologies were observed: “roof-type” with LIS, and “herringbone-type” without LIS. Therefore, it is shown that transformations both with and without LIS are possible in the present transformation, and the previous discrepancy in LIS is rationalized.