Isothermal and Adiabatic Electrostrictive Constants of NaNO₂

Abstract

The electrostrictive constants Q₁₂₂, Q₂₂₂ and Q₃₂₂ of NaNO₂ have been obtained in the para- and antiferroelectric phases by measuring the change in the dielectric constant caused by the application of a uniaxial stress. It has been found that there is a remarkable difference between the isothermal electrostrictive constant Q_i22^T and the adiabatic one Q_i22^σ. The difference is so great that the signs of Q₁₂₂^T and Q₁₂₂^σ are opposite to each other over a certain temperature range above T_N. Further the electrostrictive constants show pronounced temperature dependence near T_N, which is ascribed to the critical behavior of the electric susceptibility in this temperature region. An equation is derived which gives the pressure dependence of the transition temperature in terms of the electrostrictive constants.