Ionic conductivity enhancement during pre-crystallization in amorphous lithium ionic conductor Li2B2O4

It is found from the temperature dependence of the ionic conductivity of amorphous Li₂B₂O₄ that the ion transport process is rather complicated. At temperature below T_k (≈310°C), the ionic conductivity obeys an Arrhenius relation. Above the crystallization temperature T_c (≈410°C) ion transport is dominated by the process in the crystalline state. In between the ionic conductivity is anomalously enhanced. In this pre-crystallization range two distinguishable steps with a transition temperature at T_p (≈380°C) can be identified. At temperature between T_k and T_p, the conductivity increase is due to the redistribution of free volume. For temperature between T_p and T_c the specimen contains a small amount of crystallites but the crystallinity is less than 5%. The ⁷Li NMR spectra show that the line shape of partially crystallized amorphous material is quite similar to that of LiCl containing DSPP but in this case the second-phase particles are crystallites of the parent material.