Synthesis, characterization, and magnetic properties of mixed-valence europium-ammonia intercalation compounds of titanium disulfide

Abstract

Europium-ammonia intercalation compounds of titanium disulfide have been synthesized by reaction of EuNH 3 solutions with TiS 2, characterized by thermogravimetric analysis and powder X-ray diffraction, and investigated by electron paramagnetic resonance, magnetization, and magnetic susceptibility measurements. These materials crystallize in a 3 R-type structure in which every layer is occupied by intercalated species. The intercalation of NH 3 is accompanied by the formation of NH + 4 until a critical electron concentration of 0.22 mole el/mole TiS 2 have been transferred to the TiS 2 conduction band. Although Eu 3+ is the predominant Eu species for x > 0.001, Eu 2+ is also formed, possibly from the reduction of Eu 3+ in the van der Waals gap. These mixed-valence compounds are best described by the formulas (Eu 3+) x′ (Eu 2+) x″ (NH + 4) y′ (NH 3) y″ TiS (3 x′+2 y″+ y′)− 2 for 3 x′ + 2 x″ + y′ < 0.22 and (Eu 3+) x′ (Eu 2+) x″ (NH 3) y″ TiS (3 x′+2 x″)− n2 for 3 x′ + 2 x″ ≥ 0.22.