The inevitable flaw: imperfect crystals.

All nature is but art unknown to thee, All chance, direction which thou canst not see; All discord, harmony not understood; All partial evil, universal good; And, spite of pride, in erring reason's spite, One truth is clear, Whatever is, is right. The bonding between atoms is governed by the structure of the atoms themselves, and because all atoms of a given element are identical, we might expect the atomic arrangement in a crystal to be regular. Crystals, and indeed solids in general, were believed to be perfect for many years after the atomic structure of matter had become generally accepted. There are now so many common phenomena whose very existence is the result of a lack of perfection that it seems surprising that the concept of crystal defects developed only recently. The idea emerged in several different guises, and there was an important precursor which, although not specifically related to crystals, played a major role in heralding the new era. The first person to delve into the realm of imperfection was Alan Griffith, in 1920, following studies of the strengths of glass rods and fibres. He found that when the diameter decreases to about 10 μm, the strength of a fibre becomes markedly higher than that of a relatively thick rod. Assuming that such thin fibres must be free of the flaws that plague thicker specimens, Griffith analyzed the energy balance at idealized cracks and its dependence on applied stress. [ABSTRACT FROM AUTHOR]