H.F. Braun

High-pressure transport coefficients of the heavy-fermion superconductor CeCu2Si2

Abstract The electrical resistivity and the absolute thermoelectric power of the dense Kondo compound CeCu2Si2 were measured under very high pressures. At low temperatures, the results indicate a transition in the normal-state electronic properties around 20–30 kbar, from a strongly correlated Fermi-liquid regime (the so-called heavy-fermion state) into an IV phase. The crossover is associated with a steep increase of the critical temperature from ∼ 0.9 to ∼ 2 K. It is argued that this behavior may be due to a change from heavy-fermion to normal sd-band superconductivity.

The osmium-silicon phase diagram

Abstract The osmium-silicon phase diagram was investigated by means of X-ray powder diffraction, differential thermal analysis, metallography, microprobe analysis and electrical resistivity measurements. The existence and type of formation of the following intermetallic compounds was established: OsSi, Os 2 Si 3 and OsSi 2 . These three compounds are semiconducting. A metastable phase was found at 67 at.% silicon.

SUPERCONDUCTIVITY IN TERNARY RARE EARTH-TRANSITION METAL SILICIDES: A CRITICAL REVIEW

Abstract Ternary rare earth-transition metal silicides crystallize with a multitude of structure types. The occurrence of superconductivity among these compounds is critically examined, and their crystallography and magnetic and transport properties are discussed. New data on the ternary system La-Rh-Si are also presented.

Structural properties and band structure of heavy fermion systems: CeCu2Si2 and LaCu2Si2

The structure of CeCu2Si2, isotypic with ThCr2Si2, has been refined in a single-crystal study. The atomic parameters were used in self-consistent LMTO band structure calculations for CeCu2Si2 and isostructural LaCu2Si2. The results are analysed in terms of energy levels, charge distribution and in particular Fermi surface properties. The Ce-4f levels are situated mainly aboveEF, except near the Γ-point. The density-of-states atEF is large and heavily concentrated around the Ce-4f band. This makes local Ce 4f fluctuations possible, while interaction with the rest of the band structure is small. The comparison with LaCu2Si2 shows that the additional Cef electron is partly promoted into the non-f bands. Large enhancement factors are required to bring band results into agreement with observed specific heat and magnetic critical field. Strong Fermi surface anisotropies are pointed out for both compounds suggesting new experiments on single crystals.

LaIrSi3 with the BaNiSn3-type structure: the third ordered ternary BaAl4-type derivative in the LaIrSi system

Abstract LaIrSi3, which has a molecular weight of 415.37, is tetragonal with space group 14mm and a = 4.282(1) A , c = 9.838(2) A , V = 180.4(1) A 3 , Z = 2, Dx = 7.64 g cm−3, λ(Mo Kα) = 0.71069 A, μ(Mo Kα) = 492 cm−1 and T=293K. The structure was determined using a single crystal and was refined to an R value of 0.031 with 241 independent reflections. LaIrSi3 with the BaNiSn3-type structure is a ternary derivative of the BaAl4 type. It is compared with the two other BaAl4-type derivatives found in the same ternary system, i.e. the high and low temperature modifications of LaIr2Si2 which have CaBe2Ge2 and ThCr2Si2 structures respectively.

Phase relationships in the ternary system Ti-Au-Al at 775 K

Abstract The phase equilibria of the ternary system Ti-Au-Al were investigated at 775 K by means of X-ray powder diffraction, optical metallography, microhardness measurements and differential thermal analysis. Two ternary compounds, TiAuAl which melts congruently at 1453 K and TiAu2Al which forms by peritectic reaction at 1273 K, were identified, TiAuAl belongs to the hexagonal Ni2In structure with a = 4.410(2) A and c = 5.841(3) A . TiAu2Al is cubic with a = 3.198(2) A . From the powder patterns it was not possible to establish whether the compound is of the ordered Heusler (MnCu2Al-type) structure or of the CsCl-type structure.

Mixed valence on dilute Eu in YCu2Si2

We report measurements of electrical resistivity, thermopower, thermal conductivity, magnetic susceptibility, Mößbauer andLIII x-ray absorption of intermediate valent Eu in Y1−xEuxCu2Si2 alloys withx=0.03,x=0.07 andx=0.10. A qualitative comparison of the physical properties of dilute Eu in YCu2Si2 with concentrated Eu in EuCu2Si2 shows only slight differences; the dominant feature is a very strong variation of the Eu valence with temperature, from about 2.8 at 4 K to about 2.45 at 800 K, in the concentrated compound as well as in the dilute alloys.