A quaternary high entropy (Er1/4Sc1/4Tm1/4Yb1/4)2SiO5 monosilicate with low thermal conductivity and excellent resistance to CMAS corrosion

Abstract

The matched CTE with SiC-based ceramics composites, low thermal conductivity and better corrosion resistance against calcium-magnesium-aluminosilicate (CMAS) are the basic requirements for suitable thermal/environmental barrier coating materials for silicon-based ceramics. Rare earth silicates have better corrosion resistance against CMAS and water vapor but their high thermal conductivity and higher value of CTE limit their applications. Inspired by the high entropy effect, a new quaternary (Er_1/4Sc_1/4Tm_1/4Yb_1/4)₂SiO₅ or (4RE_1/4)₂SiO₅ monosilicate was fabricated to improve the overall performance. The TEM analysis shows the uniform mixing of powders after synthesis. The as-synthesized (4RE_1/4)₂SiO₅ monosilicate shows a matched CTE value of 3 to 5.5 × 10^–6/K with SiC-based composites due to severe lattice distortion and chemical bonding variation. The point defects, including mass mismatch and oxygen vacancies, lead to a lower thermal conductivity value (1.2 W/m·K) of (4RE_1/4)₂SiO₅ monosilicate. Furthermore, the quaternary (4RE_1/4)₂SiO₅ monosilicate also shows better resistance against CMAS at high temperatures and for longer periods. Overall, the above (4RE_1/4)₂SiO₅ monosilicate is a suitable candidate to use as T/EBC material.