Electronegativity Identification of Novel Superhard Materials

Abstract

We show that electronegativity can be used to effectively identify the hardness of crystal materials on the basis of a new microscopic model for hardness. Bond electronegativity is proposed to characterize the electron-holding energy of a bond, which is the intrinsic origin of hardness. Applying this model to c-BC(2)N materials, we confirm the proper bond composition of the experimentally observed phase of c-BC(2)N, in which the bond ratio N(C-C):N(B-N):N(B-C):N(C-N) is 3:3:1:1. A number of bonds that can or cannot form a superhard material are qualitatively distinguished, which enables us to explore novel superhard materials by screening possible elemental combinations.

Modeling hardness of polycrystalline materials and bulk metallic glasses

“…Differently, our model depends totally on the so-called polycrystalline moduli (bulk and shear modulus as well as Pugh's modulus ratio), which indeed response directly to the abilities of resistance under loading forces for polycrystalline materials. As demonstrated above, for polycrytalline materials the introduced Pugh's modulus ratio in our model plays a crucial role in elucidating plastic deformation, which is intrinsically different from all known semi-empirical hardness models [5,6,7,8,9].…”

“…It is thus highly reasonable to establish a correlation between hardness and the modulus ratio G/B in Eq. (8). Thus, we revise further the Eq.…”

“…It has been often argued [13] that hardness measurements unavoidably suffer of an error of about 10%. All these aspects add huge complexity to a formal theoretical definition of hardness [5,6,7,8,9].…”

“…During the past few years, several semi-empirical theoretical models [5,6,7,8,9] have been developed to estimate hardness of materials based on: (i) the bond length, charge density, and ionicity [5], (ii) the strength of the chemical bonds [6], (iii) the thermodynamical concept of energy density per chemical bonding [7], and (iv) the connection between the bond electron-holding energy and hardness through electronegativity [8], and (v) the temperaturedependent constraint theory for hardness of multicomponent bulk metallic glasses (BMGs) [9]. Experimentally, hardness is a highly complex property since the applied stress may be dependent on the crystallographic orientations, the loading forces and the size of the indenters.…”

Generalized evolutionary metadynamics for sampling the energy landscapes and its applications

“…We have simplified it [11,12,14] by taking bond hardness coefficients [15] as force constants (3). Bond hardness coefficients are computed from interatomic distances in a relaxed structure, and from the tabulated covalent radii and electronegativities of the atoms [12,15].…”