  We study influence of image forces on conductance of ferroelectric tunnel
junctions. We show that the influence of image forces is twofold: i) they
enhance the electro-resistance effect due to polarization hysteresis in
symmetric tunnel junctions at non-zero bias and ii) they produce the
electro-resistance effect due to hysteresis of dielectric permittivity of
ferroelectric barrier. We study dependence of ferroelectric tunnel junction
conductance on temperature and show that image forces lead to strong
conductance variation with temperature.
