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

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