Low-temperature process of the cubic lanthanide sesquisulfides:remarkable stabilization of the γ-Ce2S3 phasei

Abstract

Upon treating the corresponding oxalates with carbon disulfide (p _CS2 =130 Torr) at a heating rate of 5 °C min ^-1 , it is shown that the cubic γ-phase of pure rare-earth sesquisulfides (γ-Ln ₂ S ₃ ) can be obtained at 800 °C from samarium to holmium (also yttrium) and at 1000 °C from neodymium to dysprosium. By working on ternary sulfides Ce _2-x Ln _x S ₃ , it has been shown that the stabilization of the γ-phase occurs when the average ionic radius ranges between 1.015 and 1.104 Å at 800 °C. However, the nature of the observed sulfide phase also depends greatly on the experimental conditions, i.e. the nature of the precursor and the heating rate. At 800 °C and 5 °C min ^-1 , cerium oxalate leads to the β-phase while cerium nitrate leads to the α-phase. On the other hand, with cerium oxalate, the lower the heating rate the higher the amount of cubic γ-phase obtained.