Laser-Induced Melting and Crystal Growth of Sodium Ion Conductive β-NaFeO<sub>2</sub>

Abstract

Laser irradiation of β-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 β-NaFeO2 surface through laser irradiation with a wavelength of 1 µm. 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 β-NaFeO2 indicates a reduction reaction, suggesting that the laser-irradiated area is heated to 1500°C or higher. We confirmed that the structure change region could be controlled down to a thickness of about 10 µm by laser irradiation with varying laser power to β-NaFeO2.