MECHANISM FOR NONUNIFORM BROADENING OF THE NMR-SPECTRUM OF ORBITALLY DEGENERATE CENTERS IN CRYSTALS WITH MIXED-VALENCE IONS

A mechanism is proposed for the nonuniform broadening of the NMR spect rum of Jahn-Teller centers formed by mixed-valence ions. The effect st ems from a nonuniform distribution of the net charge and of the spin d ensity among the various nuclei of the impurity center upon the splitt ing of a degenerate term in the random crystal fields. This broadening is governed by isotropic hyperfine interactions and is distinct from the conventional mechanisms, which stem from anisotropic hyperfine int eractions at Jahn-Teller ions.