An explicit expression is derived for the indentation hardness numbers of alkali halide crystals in terms of ionic binding, combined with the theory of plastic indentation. The resistance to indentation is caused by the electrostatic faults that exist at the cores of {100} 〈1̄10〉 dislocations. The theoretical hardness is given by (cgs units) H0=0.096(e2/εb4)= 1.2×10−2C44, where e is the electron charge, ε is the static dielectric constant, b is the Burgers displacement, and c44 is the elastic shear stiffness. The theoretical hardness for NaCl is 17 kg/mm2 compared with the observed value of 16.7 kg/mm2.

Topics
Dielectric properties, Electrostatics, Chemical compounds
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© 1973 American Institute of Physics.
1973
American Institute of Physics
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