1. Andersson, S., and Galy, J., J. Solid State Chem., 1, 576 (1970).
2. Bursill, L. A., Hyde, B. G., and Philp, D. K., Phil. Mag., 23, 1501 (1971).
3. Dandekar, D. P., and Jamieson, J. C., Proc. Symp. Crystal Structure at High Pressure, 19 (Amer. Cryst. Assoc., 1969).
4. Kabalkina, S. S., Vereshchagin, L. F., and Lyatgina, L. M., Soviet Phys. JETP, 29, 803 (1969).
5. Hyde, B. G., Acta Crystallogr., A27, 617 (1971).