Tailoring the structural and electronic properties of RbLaTa₂O₇ double-layered perovskite by the rapid molten-flux synthesis route

The development of simple and scalable synthesis methods that yield new materials or unique morphologies [1, 2] opens up new possibilities for customizing surface and bulk properties for energy storage and conversion applications. Layered perovskite tantalates are a particularly attractive group of oxide materials, exhibiting interesting optical, piezoelectric, and/or photocatalytic properties. Herein, a rapid molten salt synthesis route was used to synthesize RbLaTa₂O₇ layered perovskite with improved structural and electronic properties. Different samples were prepared by using a stoichiometric ratio of Rb: La: Ta = 1:1:2, a 10-fold molar excess of molten RbCl at 1200 °C, and various reaction times (e.g., 4 h and 7 h). The effects of the flux-to-tantalate precursor ratio, the purity of the solids, and the synthesis duration on the particle growth of RbLaTa₂O₇ were examined and compared with the reference sample prepared through solid state reaction (SSR). XRD patterns revealed that the solid synthesized with molten RbCl in a short reaction time (4 h) primarily formed RbLaTa₂O₇, with only small amounts of LaTaO₄ impurities and unreacted RbCl. Increasing the reaction time to 7 h resulted in a pure RbLaTa₂O₇ phase with a tetragonal structure. The solid obtained by molten RbCl during 4 h led to well-defined platelet and rod morphologies, while a longer reaction time (7h) led to larger platelets with smooth surfaces. The molten salt approach led to products with larger specific surface areas and smaller band gaps than the reference. The CO₂-TPD profiles of molten salt-based perovskites exhibited a prominent peak in the 550 – 650 °C range, attributed to the presence of strongly basic sites. This study emphasizes the benefits of the molten salt-assisted method, which not only shortens the synthesis duration but also yields high-purity layered materials with well-controlled structural and electronic properties.