Impedance spectroscopy studies of KHSO4 above room temperature

The dielectric permittivity of polycrystalline KHSO4 was measured from 5 Hz to 13 MHz over the temperature range 51–187 °C. The corrected imaginary part of permittivity, ε″, and its real part ε′ vs. frequency clearly show a new dielectric relaxation around fmax = 1.5 * 105 Hz at 51 °C, which shifts to higher frequencies (∼ 1 MHz) as the temperatures increases. If the measurements are done when increasing the temperature, fmax decreases sharply (more than two orders of magnitude) around 164 °C; however, above this transition temperature, it continues shifting to higher frequencies as the temperature increases. However, if the measurements are done when decreasing the temperature, fmax increases abruptly around 146 °C, thus showing a hysteretic behaviour. We suggest that the observed dielectric relaxation could be produced by proton jumps and SO4− reorientation, causing distortion and changing the local lattice polarizability to induce dipoles like HSO4−.