Prepd by the action of HF on CeO2: von Wartenberg, Z. Anorg. Allg. Chem. 244, 343 (1940); by the action of F2 or concd HF on CeSi2: Sterba, Ann. Chim. Phys. [8] 2, 193 (1904); from CCl2F2 and CeO2: Pausewang, Rüdorff, Z. Anorg. Allg. Chem. 369, 89 (1969).