The compressibility of the nanolaminated M2AlC phases (space group P6(3)/mmc) with M=Ti,Zr,Hf valence electron concentration (VEC) of the M element of 4, V, Nb, Ta (VEC=5), and Cr, Mo, W (VEC=6) is systematically studied in the pressure range from 0 to similar to 70 GPa using ab initio calculations. These phases are characterized by interleaving of MC and Al layers. For VEC=4, we observe a larger compressibility along the c axis as compared to the a axis. As the VEC is increased to 5, the compressibility in the c direction decreases and becomes comparable to the compressibility in the a direction, whereas at VEC=6, the compressibility in the a direction is larger than that along the c direction. These results are consistent with recent experimental work. Based on a systematic study of the VEC-induced changes in bond stiffness, bond angle, and bond energy, we conclude that the geometric alteration of the bonding configuration in combination with the increase in M-C bond stiffness is mainly responsible for the observed compressibility change.
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