Phase formation of layered titanate-niobates KA2Ti2NbO10, A = Bi(III), Pr(III)

Layered perovskite-like compounds related to Dion-Jacobson phases with unique structural features have potential applications in various fields of science and technology, which makes these materials the subject of active research in recent years. Synthesis of Dion-Jacobson phases is carried out in various ways, including standard solid-state synthesis, hydrothermal synthesis, sol-gel method, molten salt synthesis, and others. At present, the most common method is the solid-state synthesis, due to simple interaction of compounds and an easy way to control the composition of the initial mixture. However, it is reported that not every compound with the Dion-Jacobson structure can be obtained by this method, which indicates the need for correct selection of heat treatment conditions and precursors. Thus, the aim of this study is to investigate the possibility of forming layered perovskite-like phases with the Dion-Jacobson structure of the KA2Ti2NbO10 composition, A=Bi(III), Pr(III), using the solid-state synthesis from the initial mixture of different compositions during heat treatment in a muffle furnace. The conditions of high-temperature annealing have been selected based on the data of differential thermal and thermogravimetric analysis. It has been shown that replacing bismuth(III) oxide in the initial mixture with a high-melting praseodymium(III, IV) mixed oxide increases the temperature of obtaining a single-phase sample. It has been found that a decrease in the radius of the A-site cation in the Dion-Jacobson phase structure leads to a decrease in the symmetry of the unit cell from a tetragonal one, in the case of A=Bi(III), to orthorhombic one for A=Pr(III). The decrease of the unit cell volume with a decrease of the A-cation ionic radius has been established. The obtained phases have been studied using diffraction and spectroscopic methods.