Thermodynamic Study of the SmS2–SmS1.5System

A detailed thermodynamic study of the SmS2–SmS1.5system in the temperature range 350–1000°C was performed using highquality crystals of the highest Sm-polysulfide and a sensitive static tensimetric method, a quartz Bourdon gauge with a membrane as a null-point instrument. TheP–T–xdiagram obtained has shown that the phase region covering the composition range SmS2.00–SmS1.82, which was previously described as a single grossly nonstoichiometric phase, consists of three discrete stoichiometric phases, SmS1.900, SmS1.893, and SmS1.863. The polysulfide compositions were evaluated from the tensimetric data with an accuracy of ±0.001 f. u. The thermodynamic parameters of incongruent sublimation were calculated for each polysulfide, and then the standard heats of formation were estimated for these compounds.