During the phase coexistence at the ferro-para transition of a ferro-ferro crystal, the application of an applied conjugated electric field changes the ratios of competing energies: chemical, electric, elastic ones. Then it is possible to change the shape of the phase front, the situation of domains in the ferro phase and in the ferro part of the coexistence region too. By some particular processes it is possible to create inclusions of a phase into another or some fractals inside a phase front which become subjects of studies themselves. Are then explained the thermal hysteresis of the transitions and the double hysteresis cycles. The experimentally demonstrated links between microscopic phenomena and macroscopic results clarify unexplained results and lead to revise certain models previously proposed at the para-ferro transitions.