We present results of low-temperature calorimetric and resistive measurements on the isostructural heavy-fermion compounds CeCu 2 Si 2 and CeNi 2 Ge 2 . 'Non-Fermi-liquid' effects are established which suggest the nearness of an antiferromagnetic quantum critical point (QCP) in both systems. The observed deviations from the properties of a Landau Fermi liquid (FL) may be related to anomalous energy dependences of both the quasiparticle mass and the quasiparticlequasiparticle scattering cross section. For CeNi 2 Ge 2 , a moderately heavy FL can be recovered by application of moderate values of either magnetic field or hydrostatic pressure. For p = 1.7 GPa a novel, non-superconducting, phase transition has been discovered at T 1 1 K.

Copper embrittlement by Bi atoms is a typical example of a severe detrimental phenomenon in materials science. It has recently been proposed that the strong Bi segregation in Cu can cause a liquidlike film at the grain boundaries ͑GBs͒, when the alloy is in the single-phase ͑solid solution͒ region of the equilibrium phase diagram ͓L.-S. Chang, E. Rabkin, B. B. Straumal, B. Baretzky, and W. Gust, Acta Mater. 47, 4041 ͑1999͔͒. However, a direct experimental confirmation of a liquidlike state of GBs in such a case is missing. If a liquidlike GB phase is indeed formed, the GB diffusivity should dramatically be enhanced. Radiotracer GB diffusion of 64 Cu and 207 Bi radioisotopes were measured in a set of well-characterized Cu-Bi alloys in the single-phase ͑solid solution͒ region of the equilibrium phase diagram as well as in the two-phase ͑solid + liquid͒ region. An abrupt increase of the GB diffusivities of both Cu and Bi by about two orders of magnitude was observed at certain Bi contents which are unequivocally in the single-phase region and are definitely less than that associated with the bulk solidus concentration. This critical Bi concentration was the same for selfand solute GB diffusion. With further increase of the Bi content and after exceeding the bulk solidus concentration, only marginal changes in the diffusivities of Cu as well as Bi were observed. The present results convincingly showed the occurrence of the premelting phase transition in GBs of the Cu-Bi system.

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We report on heat capacity, electrical resistance and high-temperature ESR experiments on the spin-Peierls compound α -NaV2O5. The spin susceptibility at high temperatures (T > 250 K) closely follows a Bonner-Fisher behavior with an exchange interaction J = 578 K, but differs significantly from this predictions at lower temperatures. The temperature dependence of the heat capacity can be explained assuming a sum of a linear (magnetic) and a Debye (lattice) contribution. The specific-heat jump at TSP ≈ 35 K cannot be described by the opening of a gap in mean-field approximation. The release of entropy is almost by a factor of 20 too high compared to the MF predictions of the Bonner-Fisher model for a uniform AFM spin chain with an exchange interaction of J = 578 K. The electrical resistance R(T ) can roughly be described by variable-range hopping processes and a large anomaly at the transition into the low-temperature dimerized state. From these observations we conclude that the phase transition in α -NaV2O5 at 35 K cannot be explained by a spin-Peierls transition alone.

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