Crystal Structure and Molten Salt Environment Cooperatively Controlling the Morphology of the Plate-like CaMnO 3 Template through Topochemical Conversion.

In the field of oxide thermoelectrics, perovskite CaMnO 3 ceramics have drawn plenty of attention due to their chemical stability, low cost, and environmental friendliness. By employing Ruddlesden-Poppe phase Ca 3 Mn 2 O 7 as a precursor, the plate-like CaMnO 3 microcrystals were successfully synthesized by the molten salt method combined with topochemical microcrystal conversion (TMC). The plate-like morphology of CaMnO 3 was coordinately optimized by modulating the crystal structure of MnO 2 and the molten salt environment. Plate-like microcrystals with an average size of ∼14.55 μ m and a thickness of ∼2.89 μ m were obtained by TMC reaction, demonstrating an obvious anisotropy. When β -MnO 2 was used as the raw material, a length-thickness ratio of 4.77 was obtained, which was attributed to the fact that CaMnO 3 inherited the plate-like morphology of the Ca 3 Mn 2 O 7 precursor during the TMC. The results confirm that the plate-like CaMnO 3 microcrystals with obvious anisotropy can provide excellent template seeds for high-quality CaMnO 3 -based textured ceramics.