Prepd by dissolving bismuth oxide or hydroxide in aqueous HF. May also be prepd by reduction of BiF5 with CO2 in very dil H2 at 80-150° in a Pt tube: Muir et al., J. Chem. Soc. 39, 33 (1881); v. Wartenberg, Z. Anorg. Allg. Chem. 244, 344 (1940); Aurivillius, Acta Chem. Scand. 9, 1206 (1955). Review: Kemmitt, Sharp, Adv. Fluorine Chem. 4, 213 (1965).