Preparation and Thermoelectric Properties of Some Rare Earth Chalcogenides

Abstract

Rare earth sesquisulfides were synthesized by the direct combination of the constituent elements (i.e., 2R + 3S→ R₂S₃). This method produces chemically pure products if high purity materials are used, but often produces mixed phases (1), because this is a gas (sulfur vapor) - solid (rare earth metal) reaction under the conditions the reaction is normally carried out. The gas-solid reaction is dictated by not only the reaction temperature and the composition of the reaction mixture but also the pressure of gaseous species. As is the case for many gas-solid reactions, the reaction product (RS_x) forms as a dense hard skin on the metal surface, and sulfur must diffuse through this sulfide layer into the metal core for the reaction to proceed. Many times this kinetic factor is difficult to circumvent (2).

Operated for the U.S. Department of Energy by Iowa State University under contract No. W-7405-ENG-82. This research was supported by the Assistant Secretary for Nuclear Energy, Office of Nuclear Reactor Programs, WPAS-AE-15–25.