Polarization and dielectric constant of KH2A5O4near the phase transition

The dependence of the polarization and of the dielectric constant of KH2 AsO4 on temperature and electric field is investigated in the paraelectric and the ferroelectric phases.Their behaviour is characteristic of a first-order transition. The phenomenological theory of ferroelectricity accounts for the experimental results. The coefficients of the series expansion of the free energy in terms of powers of polarization are found to be temperature dependent. The calculated value of the heat of transition agrees with experimental data.