Concentrated Jahn-Teller Systems

1 Institute of Metallurgy, Ural Branch of Russian Academy of Sciences, Amundsen Str. 101, Ekaterinburg 620016, Russia 

2Institute of Metal Physics, National Academy of Sciences of Ukraine, Vernadskogo Str. 36, Kiev-142 03680, Ukraine 

The study of oxygen diffusion in oxides with mixed-valence 3d-ions presents great interest both in theoretical and practical terms. Such systems with Jahn-Teller (JT) 3d-cations are suitable model objects for analysis of the diffusion process in degenerate or pseudo-degenerate condensed systems. The mechanism of multi-well potential formation has been explored well for JT ions [1,2] and it is possible to give a simple microscopic description of the inter-center interactions and different properties of these systems. The practical interest paid to diffusion properties of the 

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Figure 2. Crystal structure phase diagram of the Lao ssMnOx (2.82

We consider a lattice of crystal-field split ions in which some of the ions are replaced by impurities. These impurities can be either other RE-ions with different crystal-field splitting and/or different coupling parameter to the neighbouring ions or they can be ions such as La which act like holes in the lattice due to the absence of 4f electrons. In the following we want to discuss the influence of such impurities on the properties of the otherwise perfect lattice system. We shall divide the problem into two parts. First we shall consider the one impurity problem. Here the changes of the excitation spectrum are of interest (local modes, resonant modes) as well as the possible occurrence of such phenomena as giant moments or giant Jahn-Teller distortions. After this we consider finite impurity concentrations and their effect on the transition temperature. 

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