The log(σ) vs. log(ω) derivative plot used to analyze the ac conductivity. Application to fast Li+ ion conductors with perovskite structure

A criterion is proposed to analyze the dependence of conductivity data vs. frequency logσ vs. logω in ionic conductors. The derivative of experimental logσ vs. logω data enables a better differentiation of different contributions to the conductivity (bulk, grain boundary, near constant loss (NCL) and others). The usefulness of this procedure is tested for cases with different degrees of convolution between different relaxations. The criterion is applied to real data of two solid electrolytes with perovskite structure. The analysis of La0.5Li0.16Sr0.16TiO3 (LLSr) compound allowed the differentiation of bulk and NCL contributions. The analysis of the fast ion conductor La0.6Li0.2TiO3 (LLTO-06) required an enlargement of the frequency window to precisely study the bulk conductivity and correlation effects on Li motion (determination of n parameter). This methodology can be extrapolated to other solid electrolytes.

► D (log (σ))/D (log (ω)) vs. Log (ω) “derivative criterion” is used for the admittance data analysis.
► It identifies the existing relaxations and changes in the power law dispersion.
► It allows the direct extraction of conductivity parameters without fitting.
► The existence of correlated ion motions with a unique “n” (UDR) value is demonstrated.
► Evolution from UDR to the NCL regime (n=1) on increasing frequency is demonstrated.