ИСТИНА

The crystal structure of a novel ternary intermetallic aluminide Ce4Ru3Al2 was determined from the synchrotron X-ray powder diffraction data collected on an almost single-phase alloy. The compound crystallizes with an orthorhombic structure of new type: space group Pnma, lattice parameters a = 22.0592(5), b = 4.62213(6), c = 7.54309(8) Å, Z = 4. It can be presented as packing of coupled trigonal prisms with Ru-atoms located inside the prims and quadrilaterals Ru2Al2 residing in between them. The new structure is closely related to those of the equiatomic germanides YbAuGe and CaCuGe [1-2], which have similar atomic order with a total of nine crystallographic sites of the same multiplicity. However, while in the germanides, each type of atoms occupies three sites, in Ce4Ru3Al2, Ce atoms are distributed over four sites, Ru atoms occupy three sites, and Al atoms are located at two sites. A remarkable feature of Ce4Ru3Al2 is extremely small values of some Ce-Ru distances, ranging from 2.300(1) to 2.572(1) Å. Only one of the four inequivalent Ce atom exhibits a regular distance from its nearest neighbors, exceeding 3.235(1) Å. In concert with the structural characteristics, Ce4Ru3Al2 was established by means of low-temperature magnetic and electrical transport measurements to exhibit a coexistence of valence fluctuations and local moment magnetism, attributable to the Ce atom sublattices with anomalously short and normal Ce-Ru interatomic distances, respectively. Due to the ¼ fraction of Ce3+ ions with fairly stable 4f1 electronic configuration, Ce4Ru3Al2 orders antiferromagnetically at TN = 2 K and shows Kondo behavior in its electrical resistivity. In this respect, the novel aluminide resembles the gallide Ce9Ru4Ga5 that also bears in its crystallographic unit cell Ce ions with diverse valence states [3].