60 years of dislocations in ceramics: A conceptual framework for dislocation mechanics in ceramics

Abstract

High‐tech ceramics are typically engineered by controlling point defects and interfaces while one‐dimensional dislocations have found much less attention so far. Nevertheless, their impact on almost any functional property and the sudden ease to fabricate them with novel synthesis methods, such as rapid densification, brings spotlight attention to dislocations as design dimension. Although the typical brittleness of ceramics insinuates the irrelevance of dislocations for mechanical behavior, abundant literature is spread over materials, decades, and disciplines, however, often unconnected. Here, a conceptual framework for dislocation mechanics in ceramics separated into five logical aspects, (1) fundamental mobility, (2) obstacles to motion, (3) limitation by necessity of nucleation, (4) motion complexity, and (5) avoidance of competing mechanisms, brings oversight into the complex behavior. In consequence, quicker identification of the limiting step allows to estimate the potential involved more precisely and to identify open research questions with greater ease. An introduction to dislocations and the functionality involved, a look back over the last six decades, and highlights of open question are dedicated to provide a framework and bridge the gap between the attached research fields.

Dislocation toughening in single‐crystal KNbO3

“…Dislocations in ceramics have been investigated since the 1950s, most prominently by Gilman and Johnston in LiF 4–8 . An overview of the current understanding of the general dislocation mechanics in ceramics has been provided by Porz recently 9 . The understanding of dislocation nucleation, multiplication, and motion proposed by Gilman and Johnston can be borrowed to lay the foundation for the dislocation mechanics in ceramics.…”

“…[4][5][6][7][8] An overview of the current understanding of the general dislocation mechanics in ceramics has been provided by Porz recently. 9 The understanding of dislocation nucleation, multiplication, and motion proposed by Gilman and Johnston can be borrowed to lay the foundation for the dislocation mechanics in ceramics. On the other hand, recently the dislocation-mediated functional properties in ceramics have attracted increasing research interest, be it superconductivity, 10 electrical conductivity, 11 or ferroelectric properties.…”

Mechanical tailoring of dislocations in ceramics at room temperature: A perspective

“…It was suggested that engineering dislocation sources to circumvent dislocation nucleation may be a feasible way to promote dislocation plasticity in ceramics. 34 An example of such is, as discussed before, flash-sintered TiO 2 that contains a high density of dislocations and stacking faults and can exhibit plastic strain up to ∼12% during room-temperature pillar compression, 65 while conventionally sintered, dislocation-free TiO 2 samples have a fracture strain of ∼2%. In this sense, the previously presented cyclic Brinell indentation and cyclic scratching methods show consistent results: during the first cycle of indentation/scratching, fresh dislocations with a medium density are produced, which serve as effective sources for upcoming deformation cycles.…”

On the anion and cation positions within and nearby R(101¯2)$R(10\overline{1}2)$, Σ(202¯4)$\mathrm{\Sigma}(20\overline{2}4)$, and Π(101¯4)$\mathrm{\Pi}(10\overline{1}4)$ planes of α‐Al2O3 corundum structure

“…2,[36][37][38][39][40][41] A recent survey of dislocation mechanics in ceramics is given in reference. 42 Molecular dynamics simulations of edge dislocations within basal and pyramidal planes of sapphire have been conducted by many investigators, as reported, for example, in references. 43,44…”

“…This gives rise to plastic deformation by gliding of four partial dislocations separated by stacking faults 2,36–41 . A recent survey of dislocation mechanics in ceramics is given in reference 42 . Molecular dynamics simulations of edge dislocations within basal and pyramidal planes of sapphire have been conducted by many investigators, as reported, for example, in references 43,44 …”