Ferrites etc. with structures related to spinel

11 AI2O3, also formed by K K2O. 11 Fe203, also formed by Rb 3 CaO. 16 AI2O3, also formed by Sr and Ba SrO. 6 Fe203, also formed by Ba and Pb. 

(a) The relation of the structure of 0-alumina, NaAli 1O17, to that of spinel (after Beevers and Ross). Large circles represent Na, small ones O, and black circles Al. (b) The relation of the structure of magneto-plumbite, PbFei jOij, to that of magnetite Fe304 (after Adelskold). Large circles represent Pb, small ones O, and black circles Fe. 

These compounds fall into two distinct series, each formed by different stacking sequences based on three kinds of sub-unit formed from O4 or Ba03 layers  

The blocks S, M, and Y stack in various ratios and permutations but as regards sequences the units show decided preferences M is usually associated with Y (less 

The structure of BaFei20i9 is of interest as an example of a 10-layer c.p. sequence (cchhh)  

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