Origin of c-axis ultraincompressibility of Zr2InC above 70 GPa via first-principles

The elastic and structural properties of nanolaminate Zr2InC are studied by first-principles, and it is shown that, for any used modes, including the generalized gradient approximation (GGA) and localized density approximation, there always exists an ultraincompressibility along c axis between 70 GPa and 400 GPa. Such anomalous behavior is originated from the slowdown of core-valence charge transfer. The rapid shift of Zr atom along c axis also contributed much to the ultraincompressibility as it is greatly reduced once the Zr atom shift suspends along c axis above about 400 GPa. Both the elastic constants and the phononic vibrational frequencies investigations confirmed the structural unstable simultaneously. The Poisson's ratio investigations observed a higher ionic or weaker covalent contribution in interatomic bonding and the degree of ionicity increases with pressure.