Topochemical synthesis and structural characteristics of orientation-controlled (Bi0.5 Na0.5)0.94 Ba0.06TiO3 perovskite microplatelets

Abstract

Two-dimensional perovskite microcrystals have important applications in various electronic and energy devices. In this work, 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 (0.94BNT-0.06BT) microplatelets with a pure perovskite structure, (h00) orientation, good crystallinity and remarkable electromechanical strain are fabricated through topochemical microcrystal conversion from Aurivillius-structured Bi4.5Na0. 5 Ti4 O15 precursors. The formation process of the Bi4.5Na0.5Ti4O15 precursors and the topochemical conversion mechanism of the 0.94BNT-0.06BT target are systematically studied. Intermediate phases, such as Bi4 Ti3 O12 and Bi8.5Na0.5 Ti7 O27, appear before the formation of pure Bi4.5Na0.5Ti4O15 at 950 °C in a NaCl molten salt. For the topochemical microcrystal conversion process, although the Aurivillius to perovskite structural transformation is completed at 900 °C, the original single-crystal precursor platelets are replaced by polycrystalline aggregates because of extensive exfoliation and disintegration events. Such microstructural damage is healed by recrystallization via Ostwald ripening through further heating to produce single-crystal 0.94BNT-0.06BT microplatelets with flat surfaces, regular shapes and homogenous distributions of Bi, Na, Ba, Ti and O at 1150 °C. Both labyrinth and stripe-like domains can be detected from these microplatelets, suggesting the coexistence of both rhombohedral and tetragonal phases, in agreement with the X-ray diffraction analysis. Furthermore, local electromechanical strain with an amplitude of ~600 pm (at 10 V) is observed from the platelets along the <001>c direction.