Fe₃GeTe₂ and Ni₃GeTe₂ – Two New Layered Transition‐Metal Compounds: Crystal Structures, HRTEM Investigations, and Magnetic and Electrical Properties

Abstract

Abstract Fe 3 GeTe 2 and Ni 3 GeTe 2 are two new air‐stable, black‐metallic solids. They were characterized by single‐crystal X‐ray crystallography, high resolution transmission electron microscopy (HRTEM), and preliminary magnetic measurements. Both compounds crystallize in the hexagonal system [ P 6 3 / mmc , Z = 2; Fe 3 GeTe 2 : a = 399.1(1) pm, c = 1633(3) pm;Ni 3 GeTe 2 : a = 391.1(1) pm, c = 1602.0(3) pm], and represent a new structure type with a pronounced macroscopic and microscopic layer character. They show close structural relationships to iron/nickel germanium alloys. Each layer in the title compounds represents a sandwich structure with two layers of tellurium atoms covering a triple‐layer Fe 3 Ge (Ni 3 Ge) substructure on both sides. Assuming full occupancies for the Fe and Ni sites, a mixed‐valence formulation for the transition‐metal atoms according to (M 2+ )(M 3+ ) 2 (Ge 4– )(Te 2– ) 2 (M = Fe, Ni) may be concluded. A slightly reduced occupancy for one Fe/Ni position, however, indicates a more complicated local structural situation. This is confirmed by weak residual electron density in the van der Waals gap and by the results of detailed HRTEM and electron‐diffraction experiments for Ni 3 GeTe 2 . The latter results show variations in the arrangement of Ni atoms, as well as vacancies and a misfit of in‐plane disordered hexagonal layers. Fe 3 GeTe 2 shows Curie–Weiss behavior above and ferromagnetism below 230 K, while Ni 3 GeTe 2 exhibits temperature‐independent paramagnetism in the measured temperature range and a metallic behavior of the electrical resistance. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)