Aqueous sol-gel synthesis, structural, thermoanalytical studies, and conductivity properties of lithium lanthanum titanate

Abstract

Newly developed aqueous sol-gel preparation technique was applied for the synthesis of lithium lanthanum titanate with the initial composition of Li0.35La0.55TiO3. The influence of hydrochloric acid, which plays a crucial role in the formation of Li–La–Ti–O tartrate gel precursor, was also investigated. The dissolution mechanism of titanium in the concentrated hydrochloric acid and its relation with the corresponding lithium and lanthanum salts was proposed. Besides, the effect of the tartaric acid as a ligand to the formation of transparent sol and homogeneous gel precursor was discussed. X-ray diffraction revealed that below the temperature of 800 °C starts the crystallization of the final tetragonal crystal phase for Li0.3La0.567TiO3 ceramic. Rietveld refinement of the crystalline samples showed the tendency of crystallites growing with the increase of heat-treatment temperature. Besides, the single crystalline ceramic compounds heat-treated at 1000 °C and 1250 °C of temperatures were obtained only for the initial composition of Li0.35La0.55TiO3. The calculated values of the tolerance factor and structural distortion parameters in octahedral coordination of TiO6 octahedral network for tetragonal and orthorhombic crystal structures confirmed the phase transition tendency by the increase of heat treatment temperature. The scanning electron microscopy proved the formation of the dense structure of the sample for Li0.35La55TiO3 ceramic after the additional heat treatment at the temperature of 1,250 °C. In addition, the quality of synthesized ceramic was confirmed by the impedance spectroscopical measurements, which revealed that the conductivity value for bulk at the temperature of 27 °C (300 K) is equal to 0.123 S m–1.