Elements In Intermetallic Compounds Research Articles

Front Cover: Corrosion‐Free EMF Measurements of Zinc‐Based Intermetallic Compounds at Ambient Temperature (ChemPhysChem 10/2020)

The Front Cover illustrates the determination of the chemical activity of elements in intermetallic compounds by corrosion-free EMF measurements. The simple methodology allows measurements at room temperature and is applicable to a wide range of conducting materials enhancing development in heterogeneous catalysis or corrosion protection. More information can be found in the Article by R. Kriegel and M. Armbrüster.

Cr3 Triangles induced competing magnetic interactions in the new metal boride TiCrIr2B2: An NMR and DFT study

The presence of one-dimensional trigonal arrangements of chromium atoms (Cr3) in the structure of TiCrIr2B2 leads to a magnetic transition near ambient temperature. Herein we report an investigation of the nature of electronic and magnetic properties of TiCrIr2B2 via ab initio calculations together with 11B NMR Knight shift (K) and spin-lattice relaxation rate (1/T1) analysis. The presence of a characteristic rectangular powder pattern below 280K, absence of a Korringa relation, strong enhancement of 1/T1.T at low temperatures and weak temperature dependence of K indicate competition between antiferromagnetic and ferromagnetic spin fluctuations in the itinerant d-band electrons, in agreement with ab initio calculations. One-dimensional trigonal arrangements of magnetically active elements in intermetallic compounds, as is found in TiCrIr2B2, are quite rare and could lead to exotic phenomena such as spin-chirality and quantum criticality in low-dimensional frustrated lattices.

Compositional Variations In Natural Intermetallic Compounds of Pd, Pt, Cu, and Sn: New Data and Implications

Abstract We examine overall compositional ranges and substitutions of elements in intermetallic compounds of Pd, Pt, Cu, and Sn (cabriite, taimyrite, “stannopalladinite”, and tatyanaite), on the basis of (1) new results based on electron microprobe analyses of these stannides from Noril9sk (Krasnoyarskiy kray, Russia) and Lukkulaisvaara (northern Karelia, Russia), and (2) data published in the literature on natural and synthetic stannides. These results are consistent with the existence of a single and extensive field of solid solutions of the stannides of Pd-Pt-Cu, related to cabriite–taimyrite and tatyanaite, with generalized formulae (Pd,Pt) 2+ x Cu 1– x (Sn,Sb) – (Pt,Pd) 2+ x Cu 1– x (Sn,Sb), where 0 x 2+ x (Fe,Cu) 1– x (Sb,Sn). No miscibility gap is evident. An unlimited substitution of Pt-for-Pd appears to exist; in addition, Pd partly substitutes for Cu, whereas there is no evidence for the existence of a Pt-for-Cu substitution in these solid solutions. The stannides of Pd-Pt-Cu were likely deposited relatively late in the crystallization history of mineral associations, at low temperatures, likely as a result of a significant drop in temperature and increase in activity of Cu and Sn in a fractionated sulfide melt or a fluid phase. An atypical combination of relatively low levels of fugacities of O 2 and S 2 could account for the appearance of these rare compounds instead of common oxide or sulfide minerals, and could explain the observed scarcity of phases of the Pd-Pt-Cu stannides in nature.

Diffusion Studies in A<sub>3</sub>B Compounds with A15 Structure

There is a constant effort to understand the defect structure and diffusion behavior in intermetallic compounds with the A15 structure. Diffusion of elements in intermetallic compounds depends mainly on antisites and vacancies on different sublattices. In this article, we shall discuss the diffusion of elements in A3B compounds with the A15 structure.

Site preference determination in intermetallic compounds by thermal conductivity measurement

A method for the determination of site preference of substitutional elements in intermetallic compounds is proposed. It is demonstrated in Ni3Al–X alloys that the ridge direction in thermal conductivity contours in the ternary γ′ phase agrees with that of the solubility lobe of the γ′ phase in ternary phase diagrams. The ridge direction is a reliable indication of site preference of substitutional elements in intermetallic compounds. The present method is conveniently applied to a normal polycrystalline specimen with small size, and therefore, a versatile class of brittle compounds can be studied.

On the theory of X-ray K-absorption spectra oftransition elements in intermetallic compounds at theregion of near absorption edge

Calculated by the self-consistent augmented plane-wave (APW) methodwith accounting for radial factor of probability of transition, and measured experimentally, theK-absorption spectra of Fe in TiFe compound are compared in an energy range of 35 eV abovethe Fermi level. A good agreement between the theory and experiment in the main features ofabsorption curves is found. That proves the appropriateness of the band approach forinterpretation of X-ray absorption K-spectra of 3d-transition elements in intermetallic compounds.

Diffusion by anti-structure defects in non-stoichiometric intermetallic compounds with B2 and structures

Self-diffusion in non-stoichiometric intermetallic compounds with the B2 and structures has been considered. It was shown that the thermal and compositional anti-structure defects substantially affect the diffusivity forming `anti-structural bridges' for a vacancy migration without additional disordering of the intermetallic compound. While this contribution was found to have a percolation nature for both sublattices in the case of the B2 structures, the percolation is to be taken into account only for diffusion of the minor element in intermetallic compounds with the structure. The numerical calculations were carried out for the CoGa triple-defect intermetallic compound. Critical exponents and fractal characteristics of percolation clusters were estimated. Values of the threshold anti-structure defect concentrations are for B2 structures and for the -sublattice of the compound with the structure. Owing to the temperature dependence of defect concentration the percolation threshold is temperature dependent also and, e.g., corresponds to composition at T = 1323 K. The theoretical predictions are compared with experimental data.

Structural mapping of intermetallic compounds and bond character

The bond character of an intermetallic compound is expressed by two band parameters (the hybrid function H and gap reduction parameter S), which are available for crystal structure mapping of compounds. These parameters are constructed using Zunger's orbital electronegativities and the bond orbital model. It was shown that H and S correspond substantially to ionic and covalent band gaps in the one-gap model respectively. The bond character of an intermetallic compound is evaluated by the ionicity F i, which is expressed by the formula F i = H 2 (H 2 + 4S 2) . The ratio of H to S is the important parameter for determining the structural domain. Further, the two band parameters were used to determine the site preference of the alloying element in intermetallic compounds. The site preference of transition and post-transition metals in γ′-Ni 3Al and γ-TiAl determined from the parameter H S are in good agreement with previous experimental results, except for Nb in γ-TiAl. The good agreement indicates that the parameter H S can be used to predict the site preference of the alloying element in intermetallic compounds.

Statistics of solubilities of ternary elements in intermetallic compounds

La solubilite d'un element C dans un compose A x B y se produit probablement si le compose A x C y a la meme structure cristalline que A x B y . Verification de cette hypothese sur plusieurs composes intermetalliques

Effect of chemical combination on the X-ray spectra of copper

The effect of the chemical combination of an element upon its emission and absorption spectra has been the subject of many investigations by different authors. The results lead to the conclusion that the X-ray spectrum of an element is not a purely atomic phenomenon; it varies according to the state of chemical combination of the element. The effect appears to be more marked, and therefore more easily investigated, in the absorption than in the emission spectrum. Both spectra have, however, been examined and the effect in the K series measured for a number of the lighter elements from phosphorus to potassium; more recently the work has been extended to heavier elements such as iron. The present investigation deals with the K series spectra of copper, and was undertaken mainly with a view to obtaining, if possible, further information as to the nature of the chemical bond existing between elements in intermetallic compounds.