Heavy doped organic crystals ordering

Abstract

The simple model that can describe structure and charge ordering in complex doped organic crystals is proposed. We consider the quasione-dimensional model of a crystal with chains (stacks) of flat BEDT-TTF molecules. In a chain of large molecules, small molecules fill every space between large molecules. The interaction between all molecules is described by the Lennard-Jones potential. It is shown that the small dopant molecules are in the double-well potential. It is shown that in case of the electrically neutral molecules at low temperatures, there is a fluctuating structural ordering: the small molecules group in pairs near a large molecule, and the lattice period in the fluctuation domain doubles. The structure of the boundary between the fluctuation domains is defined. In case of the charged molecules, correction to electric dipole interaction makes the system essentially three-dimensional, and there is ferroelectric ordering in a chain and an antiferroelectric one between the chains. Structure of the charge domains and domain boundaries are described.