Laser-Induced Melting and Crystal Growth of Sodium Ion Conductive β-NaFeO2

Laser irradiation of beta-NaFeO2 shows local melting and crystal growth from the melt pool and sodium ion conductivity. Local melting, densification, and crystal growth were confirmed on the beta-NaFeO2 surface through laser irradiation with a wavelength of 1 mu m. Scanning electron microscopy and electron backscatter diffraction analysis confirmed anisotropic grain growth and grain boundary shrinkage in the laser-irradiated area. X-ray diffraction results suggested that the laser-irradiated area was in a low crystalline state. In addition, the precipitation of Fe3O4 in laser-irradiated beta-NaFeO2 indicates a reduction reaction, suggesting that the laser-irradiated area is heated to 1500 degrees C or higher. We confirmed that the structure change region could be controlled down to a thickness of about 10 mu m by laser irradiation with varying laser power to beta-NaFeO2.