Ultra-low thermal conductivity and excellent high temperature resistance against calcium-magnesium-alumina-silicate of a novel β-type pyrosilicates

The materials which have low thermal conductivity , a good match of coefficient of thermal expansion with SiC-based ceramics matrix composites (CMCs) and excellent resistance against calcium-magnesium-alumina-silicate (CMAS) are suitable candidates for thermal/environmental barrier coating. To fulfil the above requirements we developed a new multicomponent rare earth (Y 0.2 Dy 0.2 Er 0.2 Yb 0.2 Ho 0.2 ) 2 Si 2 O 7 or (5RE 0.2 ) 2 Si 2 O 7 high entropy ceramics pyrosilicate by a single step solid solution method. The x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed that the as-fabricated bulk composite (5RE 0.2 ) 2 Si 2 O 7 has a single phase β-type structure match well with single rare earth ytterbium disilicate (Yb 2 Si 2 O 7 ) and the different rare earth oxides mixed well with each other. The excellent coefficient of thermal expansion (4 × 10 −6 -5 × 10 −6 °C −1 ) and ultra-low thermal conductivity (0.7–1.6 W/m C) was observed as compared to other single and multicomponent high entropy ceramics composites. The (5RE 0.2 ) 2 Si 2 O 7 ceramics pyrosilicate show an excellent CMAS resistance at various temperatures (1300, 1400, and 1500) °C for 4 h compared with single principle RE disilicates. The above all mentioned results identify that this material is a suitable candidate for coating on the SiC-based ceramics composite for thermal/environmental barrier coating.