• Sub-micron La2Zr2O7 ceramic with pyrochlore structure was successfully synthesized via sol-gel and high-temperature sintering, achieving an average grain size of 895 nm.
• At 1673 K, CFAS melt rapidly infiltrates the LZO ceramic, but the formation of rod-shaped Ca2La8(SiO4)6O2 apatite and m-ZrO2 phases effectively hinders further diffusion, limiting corrosion depth.
• After 30 h of CFAS corrosion, the corrosion depth was only 160.3 μm, demonstrating excellent high-temperature resistance of sub-micron LZO ceramic.
• The findings highlight LZO ceramic as a promising candidate for thermal/environmental barrier coatings (T/EBCs) in aerospace and nuclear applications, outperforming YSZ at temperatures above 1473 K.