10-15U

An enhanced four-sublattice modification of the previously proposed model for description of lithium intercalated anatase is developed which represents thermodynamics of the system more accurately. In particular, existence of the intermediate half-filled nonpolar state (which corresponds to the intercalated anatase) has been proved as well as the conditions of its appearance have been established. A possibility of the phase separation into the empty phase and the above-mentioned half-filled one also was found in the regime of fixed concentration. Peculiarities of dielectric characteristics of the system in the critical regions of concentration and chemical potential are investigated.