08-16U

A model description of lithium intercalated anatase is presented. Such a compound is known for the coexistence of Li-rich and Li-poor phases. Performed symmetry analysis indicates the possibility of internal piezoeffect (lattice deformation accompanied by the ordering of antiferroelectric type). The set of model parameters corresponding to the lithiated anatase has been found by the analysis of the system ground state. Both Landau expansion and microscopic model approaches are available to describe the phase separation into poor and rich phases. Thermodynamics of the system is studied for the cases of constant chemical potential and constant lithium concentration. Peculiarities of dielectric, elastic and charge characteristics of the crystal in critical regions are investigated.