J. P. Burger

Absorption of hydrogen in Pd-Co and Pd-U alloys☆

Abstract The absorption of hydrogen in the structurally disordered alloys Pd 95 Co 5 , Pd 90 Co 10 and Pd 95 U 5 and in the compound Pd 3 U is studied experimentally by means of pressure-composition isotherms at temperatures between 300 K and 600 K and hydrogen pressures up to 50 bar. In spite of the fact that pure uranium readily absorbs hydrogen, whereas cobalt does not, the absorption of hydrogen is reduced more in the Pd-U alloys than in the Pd-Co alloys. In Pd 3 U no appreciable absorption could be detected at all. This remarkable reduction of hydrogen solubility in Pd-U alloys is attributed to the filling of the palladium 4d band on alloying with uranium.

Electrical and magnetic properties of palladium hydrides compared with those of pure palladium

Abstract Electrical resistivity and magnetic susceptibility are used to follow changes in electronic and atomic structure of Pd and its alloys upon hydrogenation. It is first found that H atoms go only into the octahedral sites of the Pd lattice and that the high-temperature phonon resistivity is dominated by the optical modes. The magnetic properties of Pd-based alloys with transition metal impurities are dramatically reduced in the hydrides, an effect which can be related to the reduction in the Fermi-level density of states with hydrogen content.

Kondo Lattice and Magnetic Behaviour in the CeH2+x System (0 ≤ x ≤ 0.1)

Electrical resistivity measurements on CeH2+x specimens show and incoherent and a coherent Kondo lattice behaviour above and below T ≈ 20 K, respectively. The incoherent term has a log T variation showing the influence of the crystal-field degeneracies. We observe also low-temperature anomalies related to magnetic transitions which tend to disappear when atomic disorder is introduced by quench into the sublattice of the supplementary (x) H-atoms. The coefficient of the low-temperature (T 2 K) T2-law of ρ(T) is in good agreement with the heavy-fermion model.

Electrical resistivity of rare earth dihydrides and dideuterides

Abstract The electrical resistivities of thulium, erbium, dysprosium, gadolinium and their dihydrides and dideuterides were measured below room temperature. Special attention was given to the coupling of the electrons with optical hydrogen (deuterium) vibrations. We found it to be about three times smaller than the corresponding coupling to the acoustic or host atom vibrations. The latter is also smaller in the dihydrides than in the pure metals. These data are discussed on the basis of recent theoretical models dealing with the electronic structure of the dihydrides; the implications relative to the occurrence of superconductivity and magnetism are also briefly discussed.

α-HoH(D)x: a new hydrogen-rare earth solid-solution system at low temperatures

Abstract The terminal low-temperature solubility of hydrogen in holmium has been determined resistometrically as x max = 0.03 ± 0.005 at.H(D)/at.Ho, leading to a residual-resistivity increase of Δϱ/Δx = 2.5 ± 0.5 μΩ cm/at.% H(D) and to decrease of the Neel temperature by about 2 K/at.% H(D). A quench-sensitive resistivity anomaly at 174 and at 179 K for respectively α-HoH x and α-HoD x is observed and attributed to short-range ordering of H-atoms, in analogy to other rare earth-hydrogen systems.

Electron-phonon coupling and superconductivity in metal-hydrogen systems☆

Abstract We discuss the parameters which determine the electron-phonon coupling and consequently the occurrence of superconductivity in metallic hydrides. The possibility of separating the contribution of the host metal from that of hydrogen is investigated. We then review the various hydride classes and compare the experimental results with the theoretical predictions. Special attention is paid to the isotopic effect, i.e. the change in the superconducting transition temperature Tc when hydrogen is replaced by deuterium.

Magnetic ordering in PdHx with iron impurities

Abstract We measured the magnetic ordering temperature TN of some β phase Pd1−yFeyHx alloys with x > 0.6. Two types of behaviour are observed: for y ≳ 0.04 we find that TN decreases with x and we attribute this to nearest-neighbour or short-range interactions; for y ⩽ 0.02 we observe an increase in TN with x, an effect which is also found for other magnetic impurities such as manganese and cobalt. This systematic behaviour is most probably related to the long-range interactions between impurity spins which are mediated by the conduction electrons. The positive sign of dTN/dx reflects the variation in the electronic structure of PdHx with x. A comparison with theory is carried out on this basis.