Layered perovskites as ‘soft-ceramics’

The layered perovskite KCa2Nb3O10 is shown to possess large elastic and fracture anisotropies which are explained on the basis of its structure. Its fracture toughness was measured relative to the in-basal and basal-normal directions. Combined with previously determined elastic moduli, the fracture energy release rates and associated anisotropy were determined and discussed in terms of crack deflection characteristics. The general mechanical characteristics of KCa2Nb3O10 were discussed relating to what is described as a ‘soft’ ceramic capable of sustaining considerable mechanical damage. Its high thermal stability, Tm=1464°C, and its oxidation resistance are additional features that make it attractive for high temperature applications. Anecdotal demonstrations of its softness and low damage thresholds are presented, such as might be important for cerarnic–matrix composites or machinable ceramic applications.