We present Admittance Spectroscopy measurements on two different ionically conducting materials, Gd2Ti2-yZryO7 and Li0.5-xNaxLa0.5TiO3. Electrical relaxation data have been found to be well described by stretched exponential functions of the form Φ(t) = exp(-(t/τ)1-n). In Gd2Ti2-yZryO7 the concentration of mobile ions in the whole series is very low, from 1% to 0.02 %, and we find that by strongly decreasing the density of mobile ions the value of the exponent n shows a significant decrease from 0.44 ± 0.01 to 0.16 ± 0.01. In Li0.5-xNaxLa0.5TiO3 we have investigated changes in ion dynamics when approaching the percolation threshold for lithium diffusion by increasing the number of immoble sodium ions, and found that the exponent n increases towards a value of 0.81 ± 0.01 as the mobility of lithium ions becomes more and more constrained close to the percolation threshold. Both results are discussed in terms of the importance of ion-ion correlations in the dispersive behavior of the electrical conductivity.
Bibliographical noteFunding Information:
We thank K.L. Ngai for stimulating discussions. Authors from Universidad Complutense thank financial support from MCYT (MAT2004-3070-C05) and from CAM (GR/MAT/0250/2004). Authors from CINVESTAV thank CONACYT for financial support (Grant SEP-2003-C02-44075). K.J. Moreno thanks CINVESTAV for financial support during her stay at Universidad Complutense.
- Dielectric properties
- Fast ion conduction
- Relaxation, electric modulus