Crystal structure and physical properties of a new intermetallic compound URu2Al10

We report on the existence in the U–Ru–Al system of a novel compound, URu2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, where the uranium atoms are caged in Ru–Al polyhedra, forming a clathrate-like structure. Results of the magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and specific heat, performed in a wide temperature range, are presented. No magnetically ordered state down to the lowest temperature measured has been found. On the basis of (i) the susceptibility anomaly occurring at about 50 K and (ii) the positive magnetoresistivity, growing with applied magnetic field as αBn (n ≈ 3/2), (iii) a characteristic temperature variation of the thermopower, as well as (iv) a moderate value of the Sommerfeld coefficient, a mixed-valence state of uranium in this compound has been postulated. This points to similarities between the presently studied compound and the behaviour of other Ru-containing uranium ternaries, such as U2Ru2Sn and U2RuGa8, classified earlier as valence-fluctuating type materials.