“…[31][32][33][34][35][36] Despite much progress, however, fundamental mechanisms are still debated even after 50 years of continuous study. 37 Two examples of this are the mechanism(s) for abnormal grain growth, and the classic debate over the role of magnesia as a sintering aid. [37][38][39] However, the recent discovery of interface "complexions" offers a new perspective and possible solution to such problems.…”