CERIUM INTERMETALLIC COMPOUNDS WITH 2 INEQUIVALENT CRYSTALLOGRAPHIC SITES

The low-temperature properties of five cerium intermetallic compounds, Ce2Sn5, CePtGe2, Ce5Ni6In11 and Ce4-xRu4Ge12+x (with x = 0 and 1), wh ich have two inequivalent cerium lattice sites, have been measured. Th e first three behave as trivalent systems at high temperatures (> 50 K ) but at low temperatures they exhibit some unusual properties because of the different kinds of cerium-cerium interactions, including heavy fermion, intermediate valence and magnetic order. The Ce4-xRu4Ge12+x system is unusual and displays a variety of behaviors such as heavy fe rmion, magnetic and non-magnetic atom disorder (MAD/NMAD) spin glass, and both tri- and tetravalency. The existence of independent trivalent and tetravalent cerium atoms in an intermetallic phase is unique and as far as we are aware this is the first time such a distinct valence situation has been reported for a cerium compound. Other cerium system s with multi-cerium sites reported by others are also briefly discusse d.