M 2 YSi (M=Rh, Ir): Theoretically predicted damage‐tolerant MAX phase‐like layered silicides

Searching for layered MAX phase‐like materials with properties of both ceramics and metals is a topic in its infancy. Herein, through a combination of crystal structure, electronic structure, chemical bonding, and elastic property investigations, we report two MAX phase‐like layered materials Rh 2 YSi and Ir 2 YSi. Rh 2 YSi and Ir 2 YSi have bulk modulus B of 150 and 185 GPa, respectively, which are comparable to the typical MAX phases like Ti 2 AlC, Ti 3 AlC 2 , and Ti 3 SiC 2 , but much lower shear modulus G (82 and 97 GPa for Rh 2 YSi and Ir 2 YSi, respectively) than MAX phases. The high stiffness is due to the presence of rigid Si2–M–Si3–M (M = Ir, Rh) units, while the low shear deformation resistance is due to the presence of metallic bonds and the weak bonds that link the rigid Si2–M–Si3–M (M = Ir, Rh) units. Based on the low shear deformation resistance and low Pugh's ratio, Rh 2 YSi and Ir 2 YSi are predicted as damage‐tolerant silicides and promising water vapor‐resistant interphase materials for SiC f /SiC composites if yttria or yttrium silicates are formed to protect the SiC fibers in oxygen containing environments. The possible slip systems are {0001} < 2 1 ¯1 ¯ 0 > and { 11 2 ¯ 0 } <0001> for both Rh 2 YSi and Ir 2 YSi.