Valuable imperfections in crystal lattices

Crystal lattice structures are prone to error with both localized faults of impurities or misplaced atoms, and more major long-range flaws. The chapter discusses the many ways in which a lattice may be imperfect, both at the localized level of nearby neighbours, or with larger grains, boundaries and inclusions. All types exist and variously offer beneficial or negative features for various properties of the material options and how they influence the overall properties. Some very simple, well-characterized defect structures are discussed and from there one tries to extrapolate to more complex systems. Imperfections are variously valuable or destructive, and therefore understanding and control are critical. In reality this is challenging and so the examples used here are idealized but, because they are based on simple structures, they are readily understandable.