Structural and magnetic properties of LiCrGeO4

Abstract

The crystal structure of LiCrGeO₄ has been refined using powder neutron diffraction data at 300 and 1.2 K. This compound has a spine) structure with tetrahedral sites mainly occupied by Li⁺ ions: ^IVLi_1–x-y^IVGe_x^IVCr_y^VILi_x+y^VIGe_1–x^VICr_1–yO₄ with x+y– <0.05.

Above 130 K, the magnetic susceptibility of LiCrGeO₄ obeys the Curie–Weiss law with a negative paramagnetic Curie temperature θ_p=–284 K (antiferromagnetic interactions between Cr³⁺ ions in octahedral coordination). No long-range magnetic order is observed at lower temperatures, a result which can be explained by a Cr/Ge disorder in octahedral sites and frustration effects. Crystallochemical considerations about ^IVGe^VILi^VIInO₄, of olivine-type structure, and ^IVLi^VICr^VIGeO₄ of spine)-type structure, were made considering the cationic radii; the olivine-type structure is stabilized by big cations (ca. 0.8 Å) in octahedral sites and small cations (ca. 0.4 Å) in tetrahedral sites. Cations with intermediate size (ca. 0.6 Å) in tetrahedral and octahedral sites stabilize the spine)-type structure.