B-Site Jahn-Teller Effects

The fact that Mn3+ or Cu2+ ions occupying more than a critical fraction of the spinel B sites produce distortions from cubic to tetragonal (c/a 1) symmetry has been well established, as can be seen from Table XV. In fact Satomi (552) has measured the oxygen parameters in M113O4 to demonstrate directly that it is the octahedral sites that are distorted that the tetrahedral sites resist the distortion. 

Simple extension of the Kanamori formalism leads to a linear varia- 

Unit cell as a function of composition for the systems Co i2xMn2 ]04. (After Wickham and Croft (668).) 

addition of paramagnetic Mn3+ ions into the B sites initiates A-B coupling of sufficient magnitude that N el ordering occurs in the 

Cossee and Van Arkel (133) have pointed out that tetrahedral-site Co2+ does not obey a Curie-Weiss law in the paramagnetic region because the triplet Ts and r4 levels, which are at distances of only 4000 cm-1 and 7000 cm-1 from the singlet ground state r2 (see Fig. 12), introduce a measurable high-frequency, temperature-independent component into Xm that is given by equation 17. 

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