Process for producing potassium fluoroniobate crystal and potassium fluoroniobate crystal

摘要

Disclosed herein is a method for producing potassium fluoroniobate crystals by which highly pure, large-sized potassium fluoroniobate crystals can be obtained in high yield and which is advantageous from the viewpoints of material cost and material-dissolving operation; and potassium fluoroniobate crystals. This production method comprises the first and second steps (a) and (b) of (a) adding a potassium-containing electrolyte to a starting material comprising niobium to precipitate potassium oxyfluoroniobate and/or fluoroniobate as coarse crystals, and separating the coarse crystals by filtration, and (b) dissolving the coarse crystals in a recrystallization solvent that is an aqueous solution comprising 12 to 35% by weight of hydrofluoric acid and that has been heated to a temperature of 50° C. or more, and cooling the solution to 40° C. or lower at a cooling rate of less than 20° C./h to precipitate potassium fluoroniobate as crystals.