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_0.2Dy_0.2Er_0.2Yb_0.2Ho_0.2)₂Si₂O₇ or (5RE_0.2)₂Si₂O₇ 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)₂Si₂O₇ has a single phase β-type structure match well with single rare earth ytterbium disilicate (Yb₂Si₂O₇) 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)₂Si₂O₇ 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.