SUPERCONDUCTIVITY OF FILLED SKUTTERUDITES LARU4AS12 AND PRRU4AS12

Ternary ruthenium arsenides with the skutterudite structure, LaRu4As12 and PrRu4As12 have been prepared at high temperatures and high pressu res. Electrical and magnetic properties of both compounds have been st udied at low temperatures. Superconductivity in LaRu4As12 and PrRu(4)A S(12) was found at around 10.3 and 2.4 K, respectively. The T-c of LaR u4As12 is the highest amongst skutterudite compounds. The specific hea t of LaRu4As12 has been measured between 2 and 20 K. The specific-heat data can be fit to the expression C = gamma T + beta T-3, where gamma = 73 mJ/mol K-2 and beta = 2.6 mJ/mol K-4, resulting in a Debye tempe rature (Theta) of 233 K. PrRu4As12 is the only known superconductor wi thin the family of magnetic rare-earth filled skutterudites. The arsen ic plays an important role for the enhancement of superconductivity in both arsenides. Properties of the superconductivity of LaRu4As12 and PrRu4As12 are discussed.