Synthesis and Single Crystal Growth of the Solid Solution of Perovskite-type Fluorides under Hydrothermal Conditions

The hydrothermal method has been applied to synthesize solid solutions in the pseudo-binary systems among perovskite-type fluorides (KMF₃ : M = Mn, Co, Ni, Zn and Mg) from mixtures of eo-precipitated ppwders. The continuous solid solutions existed in the all binary systems. Solid solutions in systems were produced in 2 mol KC1 solution under 100 MPa at 300°C, Transition metal ions in perovskite-type fluorides was more easily substituted by other transition metal ions than Mg²⁺ ion. Crystals of solid solutions were grown by transportation at the top of the capsule, where the temperature was lower than at the bottom. The crystals in KMnF₃-KCoF₃, KMnF₃-KZnF₃ and KCoF₃-KZnF₃ systems grew faster than the other systems. Their single crystals grew up ■ to 1.5mm in cubic′or rectangular prism form. These crystals were considered to have the same composition as that of the starting material, except for those based on KMgF₃. The lattice parameter of the mixed crystals in the KCoF₃-KZnF₃ system changes continuously with composition, indicating¹ that it obeys to the Vegard's law. The distribution of metal ions in the single crystal of KCoo,₅Zn_0i5F₃ was found to be homogeneous within experimental errors.