New compounds of the K₂NIF₄type

In the course of our investigations of new AuBO 4 compounds whose equivalent ABO 3 compounds form perovskitos, details of which will be published elsewhere, three compounds were found with the K2NIF4-typo structure. These are Sr2TiO4, Ca2MnO 4 and SrLaAl04. It may be noted that their tolerance factors, expressed in terms of the radii of the ions concerned as t = (r~+ro)/V2. (rB+ro), lie between 0.95 and 0.985. The absence of the K2NiF 4type structure in compounds with lower tolerance factors suggests that, contrary to the porovskite case, the radius of the A ion cannot be reduced much below that satisfying the geometrical condition for touching spheres (t----1). The A2BO a compounds were formed by firing the appropriate oxide, or carbonate, mixture and examinod using Co Ka radiation and a 9 cm. powder camera. Line intensities were estimated by visual comparison with a calibrated strip on which lines of known intensity were superimposed on backgrounds of varying intensity.