Phase transitions in CsHSO4 up to 2.5 GPa: Impedance spectroscopy under pressure

Phase transitions in CsHSO4 at pressures up to 2.5 GPa have been studied with the help of electrical impedance measurements. The phase boundaries have been identified with the help of calculated activation energies of electrical conductivity and dielectric relaxation time. The derived temperatures of phase transition from the low conductive phase II into super ionic phase I at pressure less than 1 GPa confirm the previous results of Ponyatovskiĩ et al. (1985) [4] and Friesel et al. (1989) [27]. The phase diagram derived in this study for pressure larger than 1 GPa differs from the data of Ponyatovskiĩ et al. (1985) [4]. The phase transitions IV–VI and VI–I occur at higher temperatures having significantly larger Clapeyron slope. The phase VII was not identified from heating cycle and appears only under cooling between phases I and VI. The phase VIII was detected at 2.5 GPa at T<350 K and only during heating.

Research Highlights
► The electrical impedance measurements have been conducted on CsHSO4 samples at high pressures and temperatures.
► The bulk electrical conductivity of CsHSO4 has been used to identify the P-T boundaries of phase transitions.
► The Clapeyron slopes of phase boundaries obtained in this study differ significantly from the previusly reported phase diagramm of CsHSO4 polymorphs.