Crystal defects or imperfections

Real, naturally occurring crystalline substances never have a perfect crystal structure -- they always show some disorder or irregularity in how their constituent particles are stacked, and such irregularities are called defects or imperfections. Defects are created during the process of crystallisation itself, and more imperfections are produced when crystallisation happens rapidly; carrying out crystallisation more slowly therefore minimises defects. In fact, a perfectly ideal crystal with no imperfections at all is possible only at the absolute zero of temperature -- above absolute zero, no crystalline material is ever 100% pure or defect-free. Whatever the specific nature of a crystal defect, the electrical neutrality of the solid as a whole is always maintained. It is also worth noting that defects are sometimes created intentionally, in a controlled way, to engineer a desired property into a crystalline solid (for example, doping a s …