Relaxation assignment in protonic conductors

The first problem is to exclude geometrical relaxation. When an electric field is applied, charges are localized on the sample under the influence of both the field and the diffusion gradient. On reversal of the field, charges find a new equilibrium so that the macroscopic dipole, the dimensions of which are those of the sample, and the new polarization are opposed to the previous one. The resulting Debye-like relaxation frequency depends on the sample thickness. 

An assignment of intrinsic relaxation phenomena can be proposed by comparing materials having similar structure and conductivity but different protonic species. A comparison of H3OUO2PO4..SHjO (HUP) and NaU02P04.3H2O (NaUP) Cole-Cole plots, for instance, helped to assign the reorientation by defects. Other relaxations are due to 

H2O and ion jumps. In MHXO4 (MDXOJ compounds, the substitution of selenium by sulphur decreases strongly the HXO. reorientation while substitution of hydrogen by deuterium reduces the proton jump relaxation to half its initial value due to the mass effect (Fig. 25.3) When cesium ions are substituted by ammonium ions, a new very slow relaxation in the 3-10 MHz region is introduced. A regular NH4 tetrahedron has no permanent dipole but a distorted ion has a dipole and the dipole intensity is strongly correlated to ferroelectric behaviour. 

The difference between and (7 is very small for the true superionic conductor phase, according to the description of conduction in terms of a quasi-liquid (free charge model). We have thus a transition from a bound charge configuration to a free charge state at the superionic phase transition. 

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