A new hydrate form of potassium chloride, KCl·H2O, is identified for the first time by in situ single-crystal X-ray diffraction under high pressure. It has a monoclinic structure with lattice parameters of a = 5.687 (7), b = 6.3969 (3), c = 8.447 (3) Å and β = 107.08 (8)° at 2.23 (4) GPa and 295 K. The structure of this hydrate has K-Cl alignments similar to the B1 phase of anhydrous KCl, while water molecules intercalate among the ionic species. The coordination structures of the K and Cl atoms can be regarded as the intermediate states between the B1 and B2 phases of KCl. This finding provides a perspective on the structural interpretation of multicomponent materials and an additional candidate for bound water in salt-water systems under high pressure, such as inside of icy bodies.
Keywords: crystal structure; high pressure; intercalation; potassium chloride; salt hydrate.
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