The influence of uniaxial compressive stress on the phase transitions and dielectric properties of NaNO₂

The effect of uniaxial stress on dielectric properties of sodium nitrite (NaNO₂) ferroelectric has been investigated. The real part of the dielectric susceptibility was measured at the frequency of 1 kHz without and on applying compressive uniaxial stress along different crystallographic directions using a uniaxial compress meter. Extraordinary changes in the dielectric constant of NaNO₂ under the influence of applied uniaxial stresses were observed for the first time. The shifts of the phase transition points _Ti and _Tc under the uniaxial stresses _σyy and _σzz were investigated. The "uniaxial pressure-temperature" phase diagram of NaNO₂ was obtained from these results. The observed phenomena were interpreted on the base of the phenomenological Landau theory of phase transitions in NaNO₂ by taking into account the uniaxial compressive stress effect. A best agreement between the theoretical predictions and experimental results has been revealed.