Thermoelectric properties of the intermediate valent cerium intermetallic Ce2Ni3Si5 doped with Pd, Co, and Cu

The nickel site of Ce2Ni3Si5, which has the orthorhombic U2Co3Si5 structure type, can be fully substituted with palladium and cobalt and partially sub stituted with copper. The volume of the lattice expands from 635 Angstrom(3 ) to 704 Angstrom(3) upon substitution with palladium while the volume cont raction with cobalt and copper substitutions are much smaller. The thermopo wer of Ce2Ni3Si5 is 32 mu V/K at room temperature and increases to 60 mu V/ K at 40 K. This relatively high thermopower is decreased by substitution of the three metals studied here. The relatively temperature independent ther mal conductivity of between 50 and 60 mW/Kcm for Ce2Ni3Si5 is decreased in magnitude by substitution of the heavier palladium, especially at temperatu res below 150 K, and is changed to typical metallic behavior by cobalt subs titution. Upon cooling from room temperature, the electrical resistivity of Ce2Ni3Si5 displays a broad plateau of 300 mu Omega cm until a precipitous drop below 120 K, indicative of coherence effects in the Kondo interactions between the cerium moments and conduction electrons. Copper and palladium substitutions result in a gradual reduction in the effects of cerium interm ediate valence, whereas cobalt substitution drives the resistivity to metal lic behavior but with a relatively large room temperature resistivity of 40 0 mu Omega cm. (C) 1999 Elsevier Science S.A. All rights reserved.