Ultra-low thermal conductivity and hydrophobic properties of high entropy β-type quaternary pyrosilicate

To raise the operating temperature of Si-based ceramic matrix composites (CMCs), thermal/environmental barrier coating (T/EBCs) materials, typically rare earth silicates are applied. However, the high thermal conductivity of each single silicate possible coating option and the mismatch of thermal expansion present a significant barrier in the development of novel materials to offer thermal insulation and environmental protection to CMCs. The entropy engineering is used to create a multicomponent equi-atomic single-phase pyro silicate with extremely low thermal conductivity and enhanced water vapor corrosion resistance at 1300 °C in 90% H₂O and 10% O₂ environment, specifically (Yb_0.25Er_0.25Tm_0.25Sc_0.25)₂Si₂O₇. X-ray diffraction patterns confirms monophase formation and the thermal parameters such as specific heat capacity, thermal expansion and thermal diffusivity were determined and microstructures were described using scanning electron microscopy before and after water vapor corrosion. The ultra-low thermal conductivity of high entropy disilicates 0.90 W/m.°C at 1000 °C and very low value of weight loss 0.0014 g/cm² is observed after 150 h corrosion time which is not reported before for even single or multicomponent high entropy rare earth disilicates.