Mechanics and electrical conductivity of dislocation-tuned ceramics

Dislocations are attracting increasing attention for their potential to tune a whole range of functional properties in ceramics. As one-dimensional line defects, they influence their environment by both their elastic strain field as well as their charged core with compensating space charge. This can be a competing approach to point defect doping. Their geometric versatility and localized impact simultaneously allow new design dimensions and pose new layers of complexity. Dislocations also severely impact mechanical properties, which demands an interrelated understanding of both their mechanics and their impact on each functional property, severely complicating research efforts. In particular, the detailed mechanisms by which dislocations impact functional properties, such as electrical and thermal conductivity, and the respective design parameters are not fully explored. Furthermore, ways to introduce dislocations into polycrystalline samples need to be developed. And lastly, the role of dislocations on the fracture toughness of ceramics needs to be revisited. Literature on all of these three questions is abundantly available. However, it is scattered over decades and a range of different materials, which impedes overview and quick identification of critical questions to be addressed. In this work, key potential is identified by first presenting a simple perspective on dislocation mechanics in ceramics. This leads to a longer discussion on room temperature plasticity and fracture toughness: Dislocations are mobile at ambient temperature in a broad range of ceramics. While these single crystals are ductile, their respective polycrystals not ductile and both behave brittle despite their ductility. A coherent explanation for this seemingly contradicting mechanical behavior is attempted while suggesting that dislocations can unexpectedly enhance the fracture toughness of ceramics substantially. Furthermore, dislocation structures are introduced into polycrystals in compression tests at elevated temperatures. This allows the rationalization of the high-temperature deformability and designing dislocation structures in polycrystals. Lastly, a conceptual framework is developed to simplify pointed discussions on the impact of dislocations on functional properties such as conductivity. In each of the three topics discussed, 1) room temperature plasticity and fracture toughness, 2) high temperature plasticity, and 3) conductivity, attempts will be made to fully embrace the mechanistic complexity. Simpler perspectives will be derived allowing easier and more accurate judgement of the potential in each of the three fields