The thermal stability and consolidation of perovskite variant Cs2SnCl6 using spark plasma sintering

Defect perovskites, a category of air and moisture stable perovskite molecular salts, have gained attention for photovoltaics in the search of alternatives to the organic lead-based photovoltaics which show exceptional photovoltaic performance but suffer significant environmental instability and toxicity of Pb. Defect perovskites also have exceptional structural flexibility and diverse crystal chemistry, and thus, display potentials as host phases for incorporating high amounts of halides such as iodine and chorine. In this study, pure Cs2SnCl6, a lead-free defect perovskite variant, was synthesized through a solution-based route that produced particles ranging from 200 to 500nm. The thermal stability of the as-synthesized Cs2SnCl6 powders was investigated using thermogravimetric analysis (TGA), demonstrating stability up to 615 degrees C, above which a phase decomposition occurs leading to the loss of constituent component of SnCl4. Consolidation of Cs2SnCl6 into dense pellets (94% theoretical density) was achieved via spark plasma sintering (SPS) at a low sintering temperature of 350 degrees C. X-ray diffraction confirms no phase decomposition in the SPS-densified perovskite pellets as a result of rapid consolidation of the SPS sintering at a short duration and lower temperature, and the TGA analysis suggest a comparable thermal stability up to 627 degrees C for the densified pellet, slightly better than the as-synthesized powders. The thermal diffusivity of Cs2SnCl6 at room temperature was determined as 0.388mm2s(-1) by laser flash measurement. This work further discussed the potential applications of the SPS-densified Cs2SnCl6 beyond perovskite photovoltaics, introducing potential nuclear separations and waste forms for chlorine.