Magnetic, calorimetric, and transport properties of Ce(Pd1-xNix)2Ge2 and CeNi2(Ge1-ySiy)2

We present results of a systematic study of the isoelectronic Kondo-lattice compounds Ce(Pd1-xNix)(2)Ge-2 and CeNi2(Ge1-ySiy)(2). With increasing x and y the hybridization of the localized 4f moments with the band states increases. Consequently the magnetic order of the Pd-rich compounds becomes suppressed, yielding a heavy-fermion behavior in CeNi2Ge2, and an intermediate valence state in Si-rich alloys. The electrical resistivity, magnetic susceptibility, and specific heat were investigated for temperatures 0.1<T<300 K. The antiferromagnetic order of localized spins in Ce(Pd1-xNix)(2)Ge-2 diminishes for x greater than or equal to 0.9 and intermediate valent behavior evolves for y greater than or similar to 0.3. We find significant deviations from Fermi-liquid behavior in a broad concentration range, which extends from x = 0.9 into the intermediate valence regime (y = 0.4). The results are compared with model predictions for magnetic systems close to a quantum critical point and for systems with frozen-in magnetic disorder (Griffiths phase). And although we find qualitatively the fingerprints of a quantum critical point, resistivity and heat capacity cannot be explained coherently within the same model. [S0163-1829(99)00219-2].