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

Abstract

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 Cs 2 SnCl 6 , a lead-free defect perovskite variant, was synthesized through a solution-based route that produced particles ranging from 200 to 500 nm. The thermal stability of the assynthesized Cs 2 SnCl 6 powders was investigated using thermogravimetric analysis (TGA), demonstrating stability up to 615°C, above which a phase decomposition occurs leading to the loss of constituent component of SnCl 4 . Consolidation of Cs 2 SnCl 6 into dense pellets (≥94% theoretical density) was achieved via spark plasma sintering (SPS) at a low sintering temperature of 350°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°C for the densified pellet, slightly better than the as-synthesized powders.The thermal diffusivity of Cs 2 SnCl 6 at room temperature was determined as 0.388 mm 2 Ás À1 by laser flash measurement. This work further discussed the potential applications of the SPS-densified Cs 2 SnCl 6 beyond perovskite photovoltaics, introducing potential nuclear separations and waste forms for chlorine. K E Y W O R D Snuclear waste, perovskites, spark plasma sintering

Perovskite-Derived Cs2SnCl6–Silica Composites as Advanced Waste Forms for Chloride Salt Wastes

“…Figure 1c shows the XRD pattern of the composite (50 wt %) after leaching for 14 days (the red curve) as compared to the as-sintered pellet before the leaching test (the blue curve). For the as-sintered composite, the dominant phase is the perovskite Cs 2 SnCl 6 , as shown by its characteristic peaks in the XRD pattern, and no phase decomposition can be observed for the as-sintered sample pellet, which is consistent with the results reported by Scott et al 24 Cs 2 SnCl 6 is a cubic Fm3̅ m (space group 225) defect perovskite structure and can degrade by decomposition and hydrolysis reaction with water. The degradation of Cs 2 SnCl 6 can be described in the following chemical reactions…”

“…The perovskite Cs 2 SnCl 6 powders were synthesized through a cost-effective and scalable wet-chemical method, which was described in detail in a previous report. 24 All the starting materials and solvents were used as received without further purification. Cesium chloride (CsCl, 99.9%), n-butyl acetate (99% min), and tin chloride pentahydrate (SnCl 4 •5H 2 O, 98%) were purchased from Sigma-Aldrich.…”

“…The perovskite Cs 2 SnCl 6 powders were synthesized through a cost-effective and scalable wet-chemical method, which was described in detail in a previous report . All the starting materials and solvents were used as received without further purification.…”

“…It is highly desirable to develop advanced waste forms with simultaneously increased waste loadings and chemical durability for chloride salt wastes, which is the goal of the current work. Metal halide perovskites and their derivatives such as Cs 3 Bi 2 I 9 and Cs 2 SnCl 6 have been proposed as potential waste forms with very high waste loadings up to 50 wt % for Cs, 59 wt % for I, and 38 wt % for Cl. , On the other hand, the metal halide perovskites suffer from intrinsic limitations of high solubility in water and low thermal stability inhibiting their applications as nuclear waste forms. Yang et al successfully encapsulated Cs 3 Bi 2 I 9 into silica matrices to form composites and core–shell structures as high as 70 wt % of metal halide perovskites with excellent chemical durability.…”

Recent Advances in Corrosion Science Applicable To Disposal of High-Level Nuclear Waste

“…Figure presents an overview of the activities. ML algorithms, particularly artificial neural networks (ANN), and DFT-based first-principles calculations have been applied in modeling radionuclide incorporation, transport, and transmutation to design promising host phases (Figure a). ,− Waste forms incorporating nonradioactive isotopes of the critical radionuclides (I, Cs, and Cl) have been experimentally demonstrated (Figure b). − Controlled static and semidynamic leaching experiments have been conducted on model systems (e.g., apatite, hollandite, perovskite, and titanate-based pyrochlore ceramics) to understand the dissolution kinetics and formation of passivation films (Figure c). − , MD simulations were performed on the designed waste forms to understand the confinement and transport of radionuclides through the channels of apatite structure types, and the calculated activation energy of migration was compared with the activation energy for dissolution measured experimentally (Figure d) . In situ synchrotron X-ray diffraction and Raman spectroscopy were applied to study the interactions of ceramic waste forms with water and to decipher their degradation mechanisms (Figure e and f) .…”