We have studied qualitatively the influence of an electric field on ferroelectric and antiferroelectric structures by means of the phenomenological theory of Landau. We have chosen a simplified example in which the antiferroelectric–ferroelectric phase change takes place without variation of the direction of the polarization. We have been able to show that without field and at increasing temperature, there are four possible cases, exhibiting the following sequences: AF → FE → PR, FE → AF → PR, AF → PR and FE → PR. We have drawn the general pattern of the phase diagrams as a function of the field and the temperature in the four cases. The comparison with the experimental results, chosen among the solid solutions of PbZrO3, shows a satisfactory fit to our theoretical results.
