Ising-Like Model For Ferroelectric Phase Transitions In Tetragonal Tungsten Bronze Compounds

Abstract

The two-component anisotropic Ising-like model was proposed to model the ferroelectric phase transitions in Tetragonal Tungsten Bronze (TTB) compounds. Using the mean-field approach we reconstructed the phase diagram of the TTB system and showed that depending on he relative strength of the interaction parameters there ferroelectric states are possible: (i) the state with y-directed polarization that corresponds to the tetragonal ferroelectric phase in TTB compounds, (ii) the state with x-directed polarization that corresponds to the orthorhombic TTB phase and (iii)  the state with superposition of x- and y- polarization components that can correspond to the not yet discovered mixed phase.