Fast Interfacial Ionic Conduction in Nanostructured Glass Ceramics

The hopping movements of mobile ions in a nanostructured ${\mathrm{LiAlSiO}}_4$ glass ceramic are characterized by time-domain electrostatic force spectroscopy (TDEFS). While the macroscopic conductivity spectra are governed by a single activation energy, the nanoscopic TDEFS measurements reveal three different dynamic processes with distinct activation energies. Apart from the ion transport processes in the glassy and crystalline phases, we identify a third process with a very low activation energy, which is assigned to ionic movements at the interfaces between the crystallites and glassy phase. Such interfacial processes are believed to play a key role for obtaining high ionic conductivities in nanostructured solid electrolytes.

Figure 1

(a) Schematic illustration of the principle of TDEFS measurements on partially crystallized glass ceramics. The inset shows an equivalent circuit diagram. (b) A representative relaxation curve: The frequency of the oscillating cantilever decreases with time due to attractive electrostatic tip-sample forces. In general, the curves can be divided into an ultrafast electronic and vibrational polarization process and a slow relaxation process.

Figure 2

TDEFS relaxation curves for a glass ceramic with 13% crystallinity in three different temperature regimes. The contributions of fast electronic and vibrational polarization are not shown, and the curves are normalized to the relaxation strength of the respective relaxation process, (a) medium temperature range (200–300 K), (b) high temperatures (above 500 K), and (c) low temperatures (below 170 K). (d) Direct comparison of relaxation curves (raw data, including fast relaxation part) under identical experimental conditions for a glass ceramic with 13% crystallinity and for a pure glass.

Figure 3

Arrhenius plot of nanoscopic TDEFS relaxation times (symbols) obtained for a glass ceramic with 13% (circles) and 42% (crosses) crystallinity, respectively. The values for the activation energies obtained from Arrhenius fits of the relation times are given in the text.