Lithium ion conductivity and dielectric relaxation in dendritic nanostructured LiTaO3 glass-nanocrystal composites

Lithium tantalate in single-crystalline and coarse-grained configurations is a poor ionic conductor and does not qualify as a solid electrolyte for lithium-based batteries. In this work, ionic conductivity was sought to be enhanced by the use of nanocrystals of LiTaO3 embedded in a borate-based glass matrix. Glasses of composition 3Li(2)O-4B(2)O(3)-Ta2O5 were formed by melt-quenching. The crystallization process was described by using isothermal crystallization kinetics, invoking the Johnson-Mehl-Avrami-Kolmogorov equation, which indicated a three-dimensional growth with an Avrami exponent of 3.5 and an effective activation energy for crystallization of 735 +/- 65 kJ mol -1. Heat treatment of the as-quenched glasses was performed between 530 and 560 degrees C, and the evolution of LiTaO3 phase was studied by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The heat treatment yielded coalesced LiTaO3 nanocrystals of 18-32 nm size, forming dendritic structures in the glass matrix. Impedance analyses of the asquenched and heat-treated glasses showed a dramatic improvement in dc conductivity (sigma(dc)), with a maximum around 3 x 10(-3) S m(-1) at 200 degrees C (sigma T-dc = 1.5 S m(-1) K) and activation energy of 0.54 eV for 530 degrees C/3 h heat-treated glasses. The values of rdc of the as-quenched glasses and of the 530 degrees C/ 3 h and 540 degrees C/3 h heat-treated glasses were about seven orders of magnitude higher than those of the single crystalline LiTaO3. Furthermore, the effect of heat treatment on lithium ion dynamics in the 40-200 degrees C temperature range was investigated by modulus formalism invoking the stretched exponential Kohlrausch-Williams-Watts function. The Li-7 magic angle spinning NMR was used to investigate lithium self-diffusion in the nanostructured glass nanocrystal composites as a function of temperature between -10 degrees C and 60 degrees C. Published by AIP Publishing