THE CRYSTAL-STRUCTURE, HEAT-CAPACITY (1.5-80 K) AND MAGNETIC-SUSCEPTIBILITY (1.6-300 K) OF LAAGGE AND CEAGGE

The crystal structures of the new ternary germanides LaAgGe and CeAgGe were determined from X-ray powder diffractometry data. These compounds crystallize in a new type of superstructure related to the CaIn2-type structure which is characterized by an ordered distribution of the smaller atoms (silver and germanium) in the unit cell and a lower symmetry: space group P6(3)mc instead of P6/mmc. The heat capacity (1.5-80 K), magnetic susceptibility (1.6-300 K) and electric resistivity (4.2-35 K) were measured. CeAgGe orders antiferromagnetically below 4.8 K, and has an electronic specific heat coefficient of 15.7 mJ mol(Ce)-1 K-2 which is typical of normal intermetallic compounds. LaAgGe exhibits an extremely low value of electronic specific heat coefficient (0.18 mJ (g-atom)-1 K-2) which is about four times smaller than that of pure copper. The large residual electrical resistivity, 1250-mu-OMEGA cm, suggests that it is a semimetal or a dirty semiconductor, but the possibility that this large value may be due to microcracks and voids cannot be ruled out.