RF-MICROWAVE DIELECTRIC-RELAXATION AND CONDUCTIVITY IN CS1-XMXHSO4 DISORDERED PROTONIC CONDUCTORS

Structural knowledge of the host lattice and of the protonic species is not sufficient for the understanding of proton transfer in solids. Dynamic data are also required. In this paper we report on RF-microwave measurements (1 MHz-18 GHz) of Cs0.9Li0.1HSO4, Cs0.75Li0.25HSO4 and Cs0.5Rb0.5HSO4 binary salts. Assignments of the relaxations observed in the epsilon'-epsilon" Cole-Cole plots are made by comparison with a previous investigation of CsHSO4.HSO4- relaxations are observed in the microwave range and conducting cation relaxations are observed in the radiofrequency range, according to predictions. Large activation energies are measured for cation jumps in poorly conducting alloys (e.g. Rb, x = 0.5) whereas very low values are observed for tetrahedron reorientations. Phase transitions evidenced by differential scanning calorimetry, vibrational spectroscopy or low-frequency conductivity are also observed. The ferroelectric nature of the 330 K transition in Cs0.9Li0.1HSO4 alloys and the role of HSO4- orientational dipole are confirmed. Conductivity models are discussed with respect to the influence of the host lattice disorder.