Crystal structure and unstable valence in a novel intermetallic phase Ce2Ru2Al.

New ternary intermetallic compound Ce 2 Ru 2 Al was prepared in polycrystalline form, and its crystal structure was determined from both powder and single crystal X-ray diffraction data. The aluminide was found to crystallize with an orthorhombic structure (space group Cmce ) with the lattice parameters: a = 5.8914(4) Å, b = 9.9603(6) Å, and c = 6.9551(4) Å. The derived unit cell is an ordered variant of the binary La 2 Ni 3 type, where one of two Ni sites is fully occupied with Ru atoms, while another one accommodates Al atoms. The structure of Ce 2 Ru 2 Al can be regarded as a sequence of atomic layers normal to b -axis. The remarkable structural feature is a short distance between Ce and Ru atoms equal to 2.7816(4) Å. Magnetic measurements revealed that Ce ions in Ce 2 Ru 2 Al possess unstable 4 f shell that leads to intermediate valence behavior of the compound. Similar valence instability was observed before for other Ce intermetallics with short Ce–Ru bonds. [ABSTRACT FROM AUTHOR]