New ternary intermetallics RE5Ru3Al2 (RE = La, Ce, Pr): Synthesis, crystal structures, magnetic and electric properties

Intermetallics RE5Ru3Al2 (RE = La, Ce, Pr) were prepared by arc melting of the elemental components with subsequent annealing at 820 K. The crystal structures were determined from single-crystal (Ce5Ru3Al2, Pr5Ru3Al2) and powder (La5Ru3Al2) X-ray diffraction at room temperature. The compounds belong to new structural types: space group R3, Z = 6, a = 13.9270(3) A, c = 8.3260(2) A for Ce5Ru3Al2 and space group I213, Z = 4, a = 9.95419(6) A and 9.8084(3) A for La5Ru3Al2 and Pr5Ru3Al2, respectively. The trigonal structure of Ce5Ru3Al2 is a distorted variant of the cubic La5Ru3Al2 and Pr5Ru3Al2 structures. An interesting feature of the Ce5Ru3Al2 are the short (2.5299(16) A and 2.5969(15) A) Ce-Ru distances. Magnetic measurements revealed the Pauli paramagnetic behavior in La5Ru3Al2 and the Curie-Weiss paramagnetism in Pr5Ru3Al2. The latter compound likely exhibits a kind of magnetically ordered state below 24 K. In turn, Ce5Ru3Al2 remains paramagnetic down to 4.2 K and shows signs of mixed valence states of Ce ions. Electrical resistivity measurements indicated simple metallic conductivity in La5Ru3Al2 and Pr5Ru3Al2, and a more complex metallic behavior in Ce5Ru3Al2.