Title: PHASE TRANSITIONS IN PSEUDOSPIN-ELECTRON MODEL WITH DIRECT INTERACTION BETWEEN PSEUDOSPINS
Authors: I.V.Stasyuk, Yu.Havrylyuk (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

The analysis of thermodynamic properties of the pseudospin-electron model in the case of zero electron transfer with the inclusion of the direct pseudospin-pseudospin interaction of ferroelectric type is performed. The equilibrium conditions in the regimes $\mu=$const and $n=$const are investigated in the mean field approximation. It is shown that the interaction with electrons leads at the fixed $\mu$ value to the possibility of the first order phase transition at the change of temperature with a jump-like behaviour of $\langle S^{z}\rangle$. In the regime $n=$const there takes place an instability with respect to phase separation in the wide range of asymmetry parameter $h$ values.

Comments: Figs. 4, Refs. 9, Tabs. 0.