Aqueous and non-aqueous Li+/H+ ion exchange in Li0.44La0.52TiO3 perovskite

Abstract

The topotactic Li+/H+ exchange in Li0.44La0.52TiO3 has been studied in different aqueous and non-aqueous media with different acidity. With this purpose, aqueous hydrochloric and nitric acid solutions and benzoic acid/ethanol solution were employed. The pristine and exchanged samples have been characterized by 1H and 7Li MAS-NMR, TGA and XRD techniques. Aqueous hydrochloric and nitric acid solutions produce the powders degradation and the subsequent formation of Li2TiO3 and La2Ti2O7 phases. A detailed analysis of the 1H MAS NMR spectra of exchanged samples indicate that Li+/H+ exchange reaction in pure water produced formation of LiOH at the particles surface, band at 0 ppm, that could subsequently carbonated after exposition in air. Furthermore the presence of other OH signals at 8, 6 and 2ppm has been related to differences on octahedral Ti-O distances, produced by La/vacancy ordering in alternating planes of perovskites. In samples immersed into benzoic acid/ethanol solution results are similar, however the amount of LiOH species in particle surface is considerable lower. The exchange degree improved when increasing exchange temperature. The mechanical grinding of powders decreases the particle size improving exchange reactions; however, grinding treatments eliminated specific NMR bands of perovskite. In ground materials new 1H NMR bands at 6 and 4ppm were ascribed to an amorphous phase.