Abstract
Using quantum-mechanical methods we calculate and analyze (tensorial) anisotropic elastic properties of the ground-state configurations of interface states associated with 5(210) grain boundaries (GBs) in cubic L1-structure NiSi. We assess the mechanical stability of interface states with two different chemical compositions at the studied GB by checking rigorous elasticity-based Born stability criteria. In particular, we show that a GB variant containing both Ni and Si atoms at the interface is unstable with respect to shear deformation (one of the elastic constants, , is negative). This instability is found for a rectangular-parallelepiped supercell obtained when applying standard coincidence-lattice construction. Our elastic-constant analysis allowed us to identify a shear-deformation mode reducing the energy and, eventually, to obtain mechanically stable ground-state characterized by a shear-deformed parallelepiped supercell. Alternatively, we tested a stabilization of this GB interface state by Al substituents replacing Si atoms at the GB. We further discuss an atomistic origin of this instability in terms of the crystal orbital Hamilton population (COHP) and phonon dispersion calculations. We find that the unstable GB variant shows a very strong interaction between the Si atoms in the GB plane and Ni atoms in the 3rd plane off the GB interface. However, such bond reinforcement results in weakening of interaction between the Ni atoms in the 3rd plane and the Si atoms in the 5th plane making this GB variant mechanically unstable.
Highlights
Grain boundaries (GBs) represent one of the most important classes of extended defects.Their properties are crucial for many aspects of solid-state materials, including, e.g., their macroscopic strength [1,2,3,4,5]
The 3 × 3 × 3 expansion of L12 unit cell was used for the bulk Ni3 Si. We found that these cells were sufficiently large to converge the shape of the density of phonon states (DPS)
Σ5(210) grain boundaries (GBs) in Ni3 Si, the computed GB energies are very similar for both compositional variants, 1.49 and 1.59 J/m2 for the Σ5(210)Ni,Ni with only Ni atoms at the interface (Figure 1a) and Σ5(210)Si,Ni with both types of atoms (Si and Ni) at the interface (Figure 1b), respectively
Summary
Grain boundaries (GBs) represent one of the most important classes of extended defects.Their properties are crucial for many aspects of solid-state materials, including, e.g., their macroscopic strength [1,2,3,4,5]. GBs are becoming even more important due to the recent proliferation of technologies providing and utilizing ultra-fine grained or nano-granular materials Materials, which significantly suffer from intergranular fracture and low ductility, are Ni-based Ni3 X intermetallic compounds with the L12 crystal structure [31,32,33] they exhibit a large potential for high temperature applications in corrosive atmospheres [34,35]. Their cohesive strengths at GB decrease with increasing valence difference between Ni and X atom and with increasing size of X atom in order
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