Preparation of Extrapure Cesium Iodide
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aration of Extrapure Cesium Iodide M. V. Mastryukova, M. N. Brekhovskikha, *, V. M. Klimovab, P. V. Kornevb, and V. A. Fedorova a
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia b State Research and Design Institute for the Rare-Metals Industry, Moscow, 111524 Russia *e-mail: [email protected] Received March 12, 2020; revised May 8, 2020; accepted May 18, 2020
Abstract—This paper presents results of a physicochemical study of the preparation of extrapure-grade (99.998%-pure) cesium iodide from a technically pure product obtained by reacting cesium carbonate and hydriodic acid. The synthesized CsI was purified in two steps, involving vacuum drying and high-temperature distillation. We calculated kinetic constants of vacuum drying and evaluated water content as a function of temperature. The final step in removing regulated impurities from CsI was high-temperature distillation. Metallic impurities in the samples thus prepared were determined using inductively coupled plasma mass spectrometry and X-ray diffraction. The results are presented for the first time. Keywords: cesium iodide, purification, distillation, drying, synthesis DOI: 10.1134/S0020168520100106
INTRODUCTION Cesium iodide is used to grow CsI:Na and CsI:Tl scintillator single crystals [1–3] and to manufacture IR-transparent glass [4, 5]. The main method for the preparation of cesium iodide-based single crystals is Kyropoulos growth [6], which allows one to obtain cylindrical ingots weighing up to several tens of kilograms. The quality of scintillation detectors produced from such materials depends significantly on the impurity composition of the starting component. Requirements for CsI purity are placed by its intended application area. Another promising application area of polycrystalline cesium iodide is perovskite solar cells with the compositions CsPbI3 [7, 8] and CsSnI3 [9, 10], which offer high conversion efficiency (up to 23%) [11] and a sufficiently low cost of photoelectric cells. Inorganic perovskite halides that absorb light in solar cells possess improved optoelectric properties, such as a large absorption coefficient, low coupling energy, long charge carrier free path, high carrier mobility, and required band gap. Requirements for CsI purity are imposed by its intended application area. It is worth noting that, in the final steps of ultrapurification in the preparation of extrapure substances, use is typically made of physicochemical methods that allow one to remove regulated elemental impurities similar in properties to the major component. In the case of water-soluble substances
whose solubility is a strong function of temperature, high-temperature or fractional distillation is typically used in the final steps [12]. Na+ and K+ ions are isomorphous with Cs+, so double high-temperature distillation is promising for final purification of cesium iodide. An intermediate step in the preparation of materials for ultrapurification by high-temperature methods is vacuum drying [13]. Howev
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