Topochemical microcrystal conversion toward Zr-substituted Ba(Zr, Ti)O₃ plate-like perovskite microcrystals

Zr-containing titanate plate-like microcrystals with perovskite structures are highly desirable for various functional applications because of their anisotropic morphology and the enhanced electrical properties induced by Zr substitution. Here, a series of (001)-oriented Ba(Zr_xTi_1-x)O₃ perovskite microplatelets with tunable Zr contents (x ≤ 0.20) and homogeneous elemental distributions were synthesized via topochemical microcrystal conversion (TMC) from Aurivillius Bi₄(Zr_xTi_1-x)₃O₁₂ precursors. The effects of Zr content x on phase structure and morphology development of both the precursors and converted microplatelets were investigated. The conversion mechanism was further elucidated using Ba(Zr_0.15Ti_0.85)O₃ as a representative by examining the structural, morphological and reaction-interface evolutions during TMC. The results demonstrate that Zr⁴⁺ ions are successfully incorporated into the BaTiO₃ lattice with controlled concentrations while preserving the platelet morphology and strong (001) crystallographic orientation. Increasing Zr content gradually reduces the lateral dimensions of the converted Ba(Zr_xTi_1-x)O₃ microcrystals, with high average aspect ratios (>8) maintained for compositions with x < 0.20. Mechanistic studies reveal that the Aurivillius-to-perovskite transformation proceeds directly without forming stable Bi-containing intermediate phase(s), and the crystalline and microstructural damages induced by the structural conversion are repaired through Ostwald ripening-driven recrystallization. This work advances the fundamental understanding of the TMC and extends the topochemical design of anisotropic perovskite microcrystals toward B-site-engineered titanate systems.