1. Meadowcroft, D. B., Energy Conversion 8, 185 (1968).
2. Meadowcrift, D. B., Brit. J. App. Phys. 2 1225 (1969).
3. Jonker G. H. and Van Santen, Physica l6 337 599 (1950); ibid 19 120 (1963).
4. Jonker G. H., Physica 20 1118 (1954); 22 707 (1956).
5. Galasso F. S., Structure, Properties and Preparation of Perovskite Type Compounds, Pergamon (1969).