High Temperature Dielectric Relaxation in Ferroelectric PbHPO 4 in the kHz Range

The complex dielectric constant,\documentclass{article}\pagestyle{empty}\begin{document}$$ \hat \varepsilon $$\end{document} , of PbHPO 4 is measured in the high temperature range of the paraelectric phase between 420 and 590 K at frequencies below 30 kHz. A dielectric response of relaxation type is observed. The real and imaginary part of\documentclass{article}\pagestyle{empty}\begin{document}$$ \hat \varepsilon $$\end{document}take on values of the order of 10 4 at 100 Hz. This response can be well described by a superposition of two Debye‐terms with relaxation times in the millisecond region. Arrhenius plots of the real part of the conductivity show that the crystal passes to a new phase at about 420 K by an activated process with an activation energy of 1.0 eV. This process is assumed to be due to the onset of hindered rotation of HPO 4 groups.