Crystal structure and the magnetic properties of CeTiGe_3

摘要

The crystal structure of the RTiGe_3 compounds (R = La, Ce and Pr) has been studied by X-ray powder diffraction methods; Rietveld refinement has been carried out on the La homologue. These compounds crystallise in the BaNiO_3 prototype structure, hP10-P6_3/mmc, also called the hexagonal perovskite (a = 6.300(1), c = 5.915(1) A for LaTiGe_3). This seems to be the first example in which an intermetallic phase adopts such a structure type which can be considered as derived from the Ni_3Sn type (anti) by a distortion of the lattice and the occupation of the quasi-octahedral 2a site at the origin of the cell (0, 0, 0) by Ti. The composition, also confirmed by microprobe analyses, was found to be strictly 1:1:3 indicating that these are line compounds, forming very likely by a peritectoid reaction. The existence of homologous compounds has been established for the lighter rare earths La, Ce and Pr. Heat capacity and magnetisation data show that CeTiGe_3 orders ferromagnetically with a Curie temperature of nearly 14 K. On the other hand a-ln T variation of the magnetic part of the resistivity below 300 K is consistent with that expected for single impurity Kondo behaviour. CeTiGe_3 is thus an uncommon example of a ferromagnetic dense Kondo lattice.