โ Scribed by M. Atanasov; U. Kesper; B.L. Ramakrishna; D. Reinen
No coin nor oath required. For personal study only.
Optical spectra and structural data of mixed crystals (\mathrm{Cu}{x} \mathrm{Zn}{1-x} \mathrm{Cr}{2} \mathrm{O}{4}, \mathrm{Ni}{x} \mathrm{Zn}{1-x} \mathrm{Cr}{2} \mathrm{O}{4}), and (\mathrm{Cu}{1-x} \mathrm{Ni}{x}) (\mathrm{Cr}{2} \mathrm{O}{4}) are reported. The optical results are used as a probe characterizing the (d)-contributions to the (\mathrm{Cu}-\mathrm{O}) bonds. The cooperative Jahn-Teller forces are analyzed, extending the statistical model by Wojtowicz to the tetrahedral sublattice. Thermodynamical and optical data are used to estimate the corresponding cooperative strain energies. A microscopic bonding model is proposed which is based on the bonding properties of the oxygen ligands with respect to (\mathrm{Cu}^{2+}) due to the presence of the "contrapolarizing" (\mathrm{Cr}^{3+}) cations. This concept makes it possible to understand the enhancement of the local Jahn-Teller distortions with increasing cooperativeness. O 1993 Academic Press, Inc.
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