Structural phase transformation and limited miscibility in Jahn-Teller systems

Immiscibility of crystal systems with Jahn-Teller (JT) ions is studied at low temperatures. Phase transformations under which concentrated JT systems are separated into phases with a high and low concentration of JT ions with structural JT transformations are analyzed. A dependence of the phase diagram topology on the ratio between the cooperative interaction energy in the JT subsystem and the intensity of random crystal fields acting on the JT ions is established. The possibility of low-temperature three-phase equilibrium of two cubic and a tetragonal phase with different concentrations of JT centers is demonstrated for a high degree of substitutional-type disorder. (C) 1999 American Institute of Physics. [S1063-777X(99)01206-2].