Journal of the American Ceramic Society, Vol.101, No.1, 365-375, 2018
M2YSi (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 Rh2YSi and Ir2YSi. Rh2YSi and Ir2YSi have bulk modulus B of 150 and 185 GPa, respectively, which are comparable to the typical MAX phases like Ti2AlC, Ti3AlC2, and Ti3SiC2, but much lower shear modulus G (82 and 97 GPa for Rh2YSi and Ir2YSi, 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, Rh2YSi and Ir2YSi are predicted as damage-tolerant silicides and promising water vapor-resistant interphase materials for SiCf/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 (11) over bar0 > and {11 (2) over bar0} < 0001 > for both Rh2YSi and Ir2YSi.
Keywords:damage-tolerant ceramics;electronic structure;interphase material;Ir2YSi;MAX phase-like materials;Rh2YSi