Fabrication and topchemical transformation mechanism of PbTiO3 microplatelets

Two-dimensional platelets of the perovskite-structured PbTiO₃ were synthesized from a layer-structured PbBi₄Ti₄O₁₅ precursor, using a topochemical microcrystal route. The PbBi₄Ti₄O₁₅ precursor showed a high aspect ratio with an average size of ～7.74 μm and thickness of ～0.29 nm. Later, PbTiO₃ platelets coexisting with Pb₄Bi₄Ti₇O₂₄ mesophase were obtained, which had a more stable Aurivillius structure and was difficult to completely convert to the perovskite structure during topochemical microcrystal conversion. The reason that the Pb₄Bi₄Ti₇O₂₄ mesophase coexisted in PbTiO₃ platelets was deeply discussed. Both the crystal structure difference between the unit cell parameters for (Pb₄Bi₂Ti₇O₂₂)^2- and the thickness for the (Bi₂O₂)²⁺ layer, and the stability of (Bi₂O₂)²⁺ layer were used to analyze the existence of Pb₄Bi₄Ti₇O₂₄ phase. However, the result showed that the stability of (Bi₂O₂)²⁺ layer was the dominant reason, because the [OBi₄]/[OPb₄] tetrahedron formed in the (Bi₂O₂)²⁺ layer due to the similar chemical properties of Pb²⁺ and Bi³⁺. The work provided deep theoretical guidance to fabricate anisotropic perovskite platform-based topchemical microcrystal conversion mechanisms.