The degree of imperfection of crystals

Abstract

An attempt is made to arrange crystals of various materials according to their degree of imperfection, derived from the apparent value of N (the Avogadro number). N has been determined for each kind of crystal according to the formula: where M is the molecular weight, c a factor related to the number of molecules per unit cell, V the volume of the unit cell and d the density of the crystal. Metals, in accordance with their mosaic structure, show a relatively high value of N and therefore a high degree of imperfection (0.06% of their volume), whilst the lowest value of N has been found for diamond, quartz, calcite and potassium chloride (prepared from a solution). Special attention is drawn to the behaviour of perfect crystals of potassium chloride (from a solution) and imperfect crystals of the same substance (from the melt): adsorption phenomena of water vapour give rise to an estimation of the thickness of mosaic blocks. A value of 6 × 10⁻⁴ cm has been found, assuming a monomolecular layer of water molecules on the internal surface.