Abstract
The obvious topological method of investigation of phase transitions in ferroelectric crystals and nonlinear phenomena is proposed. This method is based on representations about cellular complexes of system of singular points of thermodynamic potential. A full set of cellular complexes for a barium titanate is constructed. Regularities for the phase transitions induced by an external electric field are found. Opportunities of use of the method for research of structure and phase transitions in ferroelectric domain have been shown.