Beyond soft chemistry – bulk and surface modifications of polycrystalline lepidocrocite titanate induced by post-synthesis thermal treatment

Abstract

While the soft chemistry of layered alkali metal oxides is adequately understood, the effect of the post-synthesis thermal treatment on their structure, composition, and properties has been underexplored. In this article, we thoroughly investigated the bulk and surface modifications of K_0.8M_0.4Ti_1.6O₄ (M = Ni, Cu, Zn) lepidocrocite titanate thermally treated within 200 °C above its synthetic temperature under air. This practice was typically employed in e.g., specimen fabrication for physical property measurements. We observed the expansion of the interlayer distance (b/2) accompanied by a reduction in layer charge density. These findings can be explained by the deintercalation of interlayer K⁺ ions and the loss of intralayer Ti, M, and O species. Meanwhile, the enrichment of potassium and carbonate on the surfaces was evident. The slight differences in dielectric properties of the pellets thermally treated at different temperatures were attributed to the combination of bulk and surface modifications. At 10³ Hz and RT-250 °C, the maximum dielectric constants ε′_max of ∼10⁴ with the dielectric loss (tan δ) ∼0.9–1.5 were obtained for K_0.8Zn_0.4Ti_1.6O₄.