STRUCTURAL AND MAGNETIC-PROPERTIES OF LICRGEO4

The crystal structure of LiCrGeO4 has been refined using powder neutro n diffraction data at 300 and 1.2 K. This compound has a spinel struct ure with tetrahedral sites mainly occupied by Li+ ions: 1-x-y(IV)Ge(x) (VI)Cry(VI)Lix+y(VI)Ge1-x(VI)Cr1-yO4 with x - y < 0.05. Above 130 K, t he magnetic susceptibility of LiCrGeO4 obeys the Curie-Weiss law with a negative paramagnetic Curie temperature theta(p) = - 284 K (antiferr omagnetic interactions between Cr3+ ions in octahedral coordination). No long-range magnetic order is observed at lower temperatures, a resu lt which can be explained by a Cr/Ge disorder in octahedral sites and frustration effects. Crystallochemical considerations about (IV)Ge(VI) Li(VI)InO4, of olivine-type structure, and (IV)Li(VI)Cr(VI)GeO4 of spi nel-type structure, were made considering the cationic radii; the oliv ine-type structure is stabilized by big cations (ca. 0.8 angstrom) in octahedral sites and small cations (ca. 0.4 angstrom) in tetrahedral s ites. Cations with intermediate size (ca. 0.6 angstrom) in tetrahedral and octahedral sites stabilize the spinel-type structure.