Morphology control of layered Bi11Fe2.8Co0.2Ti6O33 microcrystals: critical role of NaOH concentration and citric acid

Abstract

In this article, morphology control of Aurivillius Bi₁₁Fe₃Ti₆O₃₃ (4.5-BFCTO) microcrystals was investigated in detail in the hydrothermal process, where NaOH concentration and citric acid play a critical role. When NaOH concentrations are 0.3–0.5 M, 0.6 M, and 0.7–1.5 M4.5-BFCTO microflowers, microsheets and truncated tetragonal bipyramid particles formed, respectively. For the 0.3–0.5 M-sample, (Bi₂O₂)₂CO₃(OH)₂ intermediate product, rather than (Na/Bi)₇Fe_xCo_yTi_5−x−yO_21−δ of 0.6 M and 0.7–1.5 M samples, acts as a template and is responsible for the morphology change due to the competition between OH⁻ and CO₃²⁻ ions originating from the decomposition of citric acid. For the 0.6 M and 0.7–1.5 M samples, the morphology was controlled by the Gibbs free energy along the [001] direction. Besides, the dependence of magnetic properties on the morphologies was also investigated. This research on the morphology control could serve as guidance to potentially synthesize larger BFCTO single crystals and shed light on further designing nanodevices.