Superionic phase transition in KHSO<SUB>4</SUB>: a temperature-dependent Raman investigation

Temperature-dependent Raman spectroscopic studies have been carried out on KHSO<SUB>4</SUB> single crystals in the temperature range 298-493 K. A structural phase transition driven by the lattice and molecular disorder is observed at 473 K. The spectral data enable an understanding of the nature of the lattice disorder across the phase transition leading to the superionic phase. The disorder in the HSO<SUB>4</SUB><SUP>&#8722;</SUP> polymeric hydrogen-bonded chain leading to a higher symmetry in the high temperature phase is clearly captured from our Raman results. The internal S-OH and S-O stretching modes and, to a limited extent, the external modes throw light on the disorder mechanism and the enhancement of conductivity after transition