Ceramic materials with high dislocation density: Possible influence on ionic conductivity and fracture toughness

All-dislocation-ceramics are theoretically proposed as solid electrolytes filled with appropriate dislocation-pipes (which are considerably wider than dislocation-cores) for high ionic conductivity because ionic conductivity along dislocations could be a few orders of magnitude higher than that in the bulk. The reasons are the accumulation of vacancies around a dislocation and the reduction of energy barrier for ionic conduction by the strain field especially for already vacancy-rich conductors. However, the situation is more complex because dislocations could decrease or increase ionic conductivity for the case of positively charged oxygen-vacancy conduction along positively charged dislocations depending on the roles of the strain field and the electrostatic repulsion of oxygen-vacancies. It is expected that fracture toughness is increased by the presence of dislocations. According to the numerical simulations of evolution of mobile and immobile dislocation densities during cold sintering (liquid-phase sintering under applied pressure), high-density dislocations required for all-dislocation-ceramics could be produced.