Segregation behavior of the intermetallic compounds ZrNiAl,YNiAl and UNiAl

The surface layers of the intermetallics ANiAl (A = Zr, Y, U), exposed to the ambient air, residual gases and oxygen, were investigated by X-ray photoelectron spectroscopy. The surface and the oxidation energies of the metal components were considered as the possible driving forces for the surface decomposition. A “rule of reverse stability” exists for the three isostructural compounds, i.e., the less stable one (UNiAl) exhibits the most significant segregation. An extrapolated degree of segregation of the air-exposed intermetallics yields a good agreement with previously proposed quantitative model.     

Hydrides of intermetallic compounds

Aspects of the progress over the recent years on hydrides of intermetallic compounds are reviewed with emphasis on structure, stability, solid-state properties, catalysis, and kinetics. Some new routes to an understanding of hydride phenomenology are indicated. Generally speaking hydrides represent but one special aspect of intermetallic compounds. They are, however, unique as model systems for questions concerning the stability of intermetallics in general, as thermodynamic data become more readily available during synthesis than is the case with most other metallic systems. Stability criteria are exemplified on model systems chosen to represen instructive or extreme cases. Hydrides are, moreover, unique with respect to the unusual properties of hydrogen as a “metallic” component, especially concerning such characteristics as mass (light), size (ranging from average to exceedingly small as a proton) and electronegativity (relatively high and comparable to B). This promises a wealth of special solid-state properties concerning magnetism, electrical conductivity or superconductivity. Some selected examples in this direction are discussed with emphasis on questions pertaining to the electronic state and the stability of the hydrides. The kinetics of compound (hydride) formation are often extraordinarily fast around ambient conditions opening this facet of intermetallics to rigorous study. Also intriguing new catalytic activity has been identified with metal hydrides implicating in one way or another the special surface properties of metal hydrides. Finally, metal hydrides are gaining in importance with respect to technological applications within a projected hydrogen economy (H or heat storage, electrochemical cells, etc.). Many of the fundamental aspects of metal hybrides have therefore become of practical relevance. Financial support by the Department of Energy, Division of Basic Energy Sciences, is acknowledged.     

Depth dependence of the anomalous thermal behavior of Cu(110)

We report the results of a mirror electron microscope low energy electron diffraction (MEM-LEED) study of anomalous thermal behavior caused by enhanced thermal vibrational motion on a clean Cu(110) surface. The enhanced vibrational amplitudes cause diffracted intensities to deviate from simple Debye-Waller behavior. These deviations become apparent between 550 K and 600 K; i.e. at about 0.45 of the bulk melting temperature. Because of the finite penetration of low energy electrons, LEED intensities contain information about both surface and subsurface order. Our LEED results are analyzed to extract this information using a kinematical model in which the electron attenuation and the depth and temperature dependent vibrational amplitudes are parametrized. For a large range of model parameters, we conclude that by 850 K large anharmonic vibrations are present in several layers and at least two subsurface layers may have melted.     

Investigation of the effective parameter of spin-orbital interaction in intermetallic compounds of the Tb-In system in the paramagnetic region

The normal, R₀, and anomalous, R_S, components of the Hall coefficient are determined from experimental temperature dependences of the Hall coefficient, magnetic susceptibility, and specific electrical resistance of the Tb ₂ In and Tb ₅ In ₃ intermetallic compounds. The band parameters, radius of the Fermi sphere k_F, and the Fermi energy E_F of the examined samples are calculated for the known values of the normal component of the Hall coefficient R₀. Values of the anomalous component R_S of the Hall coefficient and specific electrical resistance ρ are used to calculate the effective spin-orbital interaction parameters λ_SO for the intermetallic compounds. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 47–49, March, 2007.     

Thermal expansion and magnetostriction in an anomalous Gd intermetallic compound

Thermal expansion and forced magnetostriction measurements are reported on two Gd intermetallic compounds which order magnetically below 10 K. The relative influence of the electronic, lattice and magnetic degrees of freedom was determined using results obtained on a non-magnetic isostructural compound. A Grüneisen analysis revealed that whilst the magnetic contribution to the specific heat is similar for both Pd₂GdIn and Cu₂GdIn the spontaneous magnetostriction was significantly smaller in the Pd compound. Forced magnetostriction measurements suggest that the thermal expansion in Pd₂GdIn is primarily associated with spin fluctuations in the Pd 4d band. It is suggested that these additional degrees of freedom give rise to the enhanced specific heat observed in Pd₂GdIn. Received 28 July 1999     

Magnetic anomalies of thermal expansion in (rare-earth) Ni2 intermetallic compounds

The thermal expansion of eight RENi₂ intermetallic compounds (RE = La, Nd, Sm, Tb, Dy, Ho, Er, Tm) and YNi₂ have been measured between 3.8 and approx. 300 K. The anomalies found at the paramagnetic-magnetically ordered phase transition have allowed an accurate determination of the Curie temperatures. From the low temperature comparison of the thermal expansion of the light RE compounds with that of LaNi₂, and of the heavy RE compounds with that of YNi₂, the Debye temperatures have been obtained. In the case of the compounds DyNi₂, TbNi₂ and HoNi₂ the contributions from crystal field and exchange interactions to the spontaneous volume strain at the magnetically ordered phase have been calculated, the agreement between experiment and calculation being good.     

PAC measurements of In-Pt intermetallic compounds

The quadrupole interaction parameters for¹¹¹Cd in In₇Pt₃ and In₃Pt₂ compounds were measured by TDPAC in the temperature range 80–1000 K. The EFG temperature behavior follows theT ^3/2 relation.     

Hall effect of Ce intermetallic compounds

Hall effect measurements between 300 K and 4.2 K for CeAl₂, CeSn₃, CeCu₂Si₂, CeBe₁₃, CePd₃, Ce(Pd_0.88Ag_0.12)₃ and CeRh₃ are discussed in detail. The skew scattering contribution to the Hall coefficient observed in some of these compounds is discussed in terms of the existing theories.     

Magnetic phase transitions in layered intermetallic compounds

Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn₂Si₂ and RMn₆Sn₆ (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn–Mn and Mn–R exchange interactions.     

Magnetism and superconductivity in intermetallic uranium compounds

Superconductivity, spin-fluctuation effects and magnetic order are reviewed for intermetallic compounds of uranium with d-transition elements. Large values for the effective mass of the pairing electrons are deduced from critical field studies on the superconducting compounds. Magnetism in the 5f-electron compounds is strongly anisotropic even for paramagnetic materials. Magnetic order does not frequently occur in these intermetallics, spin fluctuations are often observed. A unique combination of spin-fluctuation phenomena and superconductivity is met in UPt₃.     

Study on mechanical behavior and electronic structures of Al-Cu intermetallic compounds based on first-principles calculations

In this paper, we use first-principles calculations to study the correlation between mechanical behaviors and electronic structures of Al-Cu intermetallic compounds. We find that in general, the ductility of intermetallic compounds decreases with the increase in Cu content, while the corresponding work function increases but densities of states decrease. Moreover, homogeneous and symmetrical or small anisotropic charge distributions correspond to small brittleness. The present study therefore suggests that the primary origin of brittleness in intermetallic compounds can be well related to their electronic structures.     

Electron work function of intermetallic compounds in the cerium-cobalt system

The concentration dependences of the electron work function for lithium samples in the cobaltrich region of the state diagram of the Ce-Co binary mixture is studied by the contact potential difference method at 20°C. It is shown that the electron work function isotherm has the shape of a broken line with kinks corresponding to intermetallic compounds formed in the cerium-cobalt binary system.     

X-Ray isochromats of some chromium intermetallic compounds

A systematic investigation of the fine structure near the short wavelength limit of the continuous X-ray spectrum for the chromium compounds CrB, CrSb, and Cr₂Te₃ has been made by means of a vacuum spectrometer with a curved (radius one meter) topaz crystal. Information about the density of states in the conduction band and the characteristic energy losses in these compounds is given.     

Magnetic properties of some Cr-Ga intermetallic compounds

Magnetic susceptibility measurements in the range 10 – 300 K on the compounds Cr₃Ga, CrGa, Cr₅Ga₆ and CrGa₄ are reported here. All except CrGa₄ appeared to be Pauli paramagnetic, but CrGa₄ appeared to be basically diamagnetic with a parasitic weak ferromagnetic component.     

Characterization of Zn−Fe intermetallic compounds

Zn?Fe intermediate phases have been investigated. The distribution of quadrupole splittings P(QS) was determined from the Mössbauer spectrum: the P(QS) gives evidence for two different iron sites in the γ phase. The analysis of Mössbauer spectrum taken in an applied magnetic field shows the negative sign of electrical field gradients is present.     

Magnetic order in TbNiAl and TbCuAl intermetallic compounds

Polycrystalline samples of the ternary intermetallics TbNiAl and TbCuAl are investigated by means of magnetization and neutron diffraction measurements. When Cu replaces Ni in the crystal structure, the magnetic behaviour is shown to be totally different, although both elements are non-magnetic. Analysis of the neutron spectra by the Rietveld refinement method gives evidence that TbNiAl orders antiferromagnetically whereas TbCuAl becomes ferromagnetic. Frustrated spins at the Tb atoms are found only in the TbNiAl compound. Their alignment changes at a second magnetic transition. The magnetic structures and the transition temperatures are discussed.     

On the valence and lattice parameter in cerium intermetallic compounds

Experimental data concerning valence and lattice parameter in cerium intermetallic compounds are discussed using the concepts of electronic charge screening and charge transfer between the rare earth and the transition element.     

Magnetic order in TbNiAl and TbCuAl intermetallic compounds

Polycrystalline samples of the ternary intermetallics TbNiAl and TbCuAl are investigated by means of magnetization and neutron diffraction measurements. When Cu replaces Ni in the crystal structure, the magnetic behaviour is shown to be totally different, although both elements are non-magnetic. Analysis of the neutron spectra by the Rietveld refinement method gives evidence that TbNiAl orders antiferromagnetically whereas TbCuAl becomes ferromagnetic. Frustrated spins at the Tb atoms are found only in the TbNiAl compound. Their alignment changes at a second magnetic transition. The magnetic structures and the transition temperatures are discussed.     

Mössbauer study of the Fe-Si intermetallic compounds

Fe-57 Mössbauer spectra of the silicon-rich intermetallic compounds of the iron-silicon system have been measured. Characteristics of hyperfine structure (i.e. the isomer shift and quadrupole splitting) of the FeSi (q.s. 0·499±0002 mm/s), α-Fe-Si₂ (q.s. 0·813±0·033 mm/s) and β-FeSi₂ (q.s. 0·420±0·003 mm/s) are given, by means of which the transformations between those phases at different heat treatments were followed. A possible application to the study of iron diffused into silicon is shown.