Infrared spectroscopy investigation of theCsHSeO4superionic phase transition

The temperature dependence of the polarized infrared reflectivity spectra of cesium hydrogen selenate is reported between room temperature and 170 °C, and analyzed in the framework of the four-parameter model of the dielectric function. The results of the simulation show that the hydrogen-bond breaking starts far below $T_C$ and the ratio η of protons involved in H-bond chains follows the law $\eta \mathrm{}\left(T\right)=\exp [E/(T-T_0\left)\right]$ with $E=5.3\mathrm{}\mathrm{K}$ and $T_0=129\mathrm{}°\mathrm{C}.$ The protonic superionic phase transition is shown to occur at a topological threshold from a one-dimensional structure of H bonding to a structure of liquidlike nature. Such a microscopic mechanism, i.e., H-bond breaking, is consistent with previous results and explains the peculiar behavior of the elastic properties.