A Crystallographic Investigation of Calcium Diferrite

Calcium diferrite has been prepared at 1220°C in air. The lattice constants at 25° C of calcium diferrite have been determined by X-ray powder data and have been based on the hexagonal system. They are a= 5.992 ± 0.004 A and co = 31.121 ± 0.008 A. The coefficients of thermal expansion were evaluated by X-ray methods between-130° and 25°C to be α1= 9.2 × 10−6 per°C and 3= 23 × lop6 per °C, where a3 is along the principal axis and α is perpendicular to it. The diferrite is ferromagnetic with a Curie point of 135°C. Comparison of the results obtained from the present work with those of some recent studies shows that the X-ray data given by previous workers on compounds claimed to be Ca3FeleO15, Ca4Fe17O29, and Ca4Fe4O25 are for calcium diferrite. The present work, however, also indicates that when mixtures of calcium diferrite plus ferrous oxide (up to 6 wt%) are heat-treated at 1220°C, a new phase appears together with the diferrite.