In the sintering of ceramic materials, abnormal grain growth is often viewed as an undesirable phenomenon because rapidly growing grains may lower the hardness of the bulk material through Hall-Petch-type effects. However, the controlled introduction of dopants to bring about controlled AGG may be used to impart fibre-toughening in ceramic materials. Additionally, AGG is undesirable in piezoelectric ceramics, as it may degrade the piezoelectric effect.