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 pressures. Electrical and magnetic properties of both compounds have been studied at low temperatures. Superconductivity in LaRu4As12 and PrRu(4)AS(12) was found at around 10.3 and 2.4 K, respectively. The T-c of LaRu4As12 is the highest amongst skutterudite compounds. The specific heat 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 temperature (Theta) of 233 K. PrRu4As12 is the only known superconductor within the family of magnetic rare-earth filled skutterudites. The arsenic plays an important role for the enhancement of superconductivity in both arsenides. Properties of the superconductivity of LaRu4As12 and PrRu4As12 are discussed.