Liquid state properties and solidification features of the pseudo binary BaS-La₂S₃

The high temperature thermodynamic properties of chalcogenides materials based on BaS remain elusive. Herein the pseudo binary BaS-La₂S₃ is investigated above 1573 K. The liquid properties of BaS-La₂S₃ are measured by means of high resolution in-situ visualization coupled with thermal arrest measurements in a thermal imaging furnace. This enables to report the first observation of such melts in a container-less setting. The melting points of BaS and La₂S₃ are revisited at 2454 K and 2004 K respectively. La₂S₃ demonstrates a high stability in its liquid state, in strike difference with the sublimation observed for BaS. BaS is however partially stabilized with the addition of few percents of La₂S₃. The remarkable chemical and thermal stability of La₂S₃-rich samples contrasts with the partial decomposition and high vapor pressure observed for BaS-rich samples. Observations and analysis of the solidified samples suggest three different solid solutions. Solid and liquid densities are investigated along the different compositions, supporting a first estimate of the volumetric thermal expansion coefficient for La₂S₃.