Local structures around Cu2+and Zn2+ions related to cooperative jahn-teller distortions in dilute systems of K2Cux.Zn1F4

The structural properties of the dilute systems of K2Cu x Zn1 x F4 have been studied by means of X-ray absorption fine structure (EXAFS) for the Cu-K edge and Zn-K edges. It is found that there are rigid-like Jahn-Teller distortions of the CuF6 octa-hedra in the region of 0.0 < x ≤ 1.0. It is also found that, in dilute systems, the ZnF6 octahedra at least show two kinds of shapes, of which one is characterized to have a 2-fold symmetry axis and the other to have a 4-fold symmetry axis in the (x-y) plane. Thus, the inner strains induced by the replacement of the Zn atoms by the Cu atoms are localized around the Zn atoms, and can be reduced by the appearance of the former ZnF6 octahedra showing a pseudo Jahn-Teller distortion.