Ionic compounds bulk modulus

The appeal of this approach is in the small number of parameters which need be put into the calculation (those of Table 12-2, which are also given in the Solid State Table) as well as in the remoteness-of-origin of these parameters relative to the mechanical properties of the ionic crystals being studied. We use that approach though it is quite crude. Notice, in particular, that it predicts the same properties for complementary skew compounds such as NaCl and KF, which we shall see is far from true. Much higher accuracy could be obtained by fitting a and i to the observed spacing and bulk modulus for each compound. That choice is better... 

All the expressions indicate that shorter and denser chemical bonds as well as smaller ionicity should favor hardness. In order to obtain a compound with large bulk modulus, one must find such a covalent compound that has both shorter bond length and smaller ionicity, and high compactness in atomic arrangement inside. Thus, the atomic CN-imperfection-induced bond contraction should contribute directly to the hardness at the surface or sites surrounding defects. Therefore, a nanometer-sized diamond is expected to be 100 % (0.88 — 1) harder than the... 

In order to obtain a compound with large bulk modulus, one must find such a covalent compound that has both a shorter bond and smaller ionicity, and high compactness in internal atomic arrangement [35]. 

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