In-situ detection of a complexion transition and related microstructural changes in alumina using high-temperature mechanical spectroscopy

Complexion transitions induce changes in grain boundary kinetics and microstructural evolution, yet their direct experimental detection remains challenging. In this study, high-temperature mechanical spectroscopy (1300–1600 K) is explored as an in-situ probe of grain growth and potential complexion transitions in 500 ppm La-doped alumina. A fully dense spark plasma sintered sample without grain growth exhibits an exponentially increasing mechanical loss background above 1350 K. Thermal activation of the background was analyzed with a master curve method. Temperature scans, however, fit no unique master curve and yield unphysical apparent activation energies, indicating a dynamically evolving system with structural and/or population changes at grain boundaries. Isothermal frequency scans reveal non-Arrhenius behavior, suggesting interfacial microplasticity resembling glass-like dynamics. This response could be explained with an order–disorder complexion transition or activation of additional disconnection modes. EBSD analysis confirms grain growth and grain boundary changes, supporting the occurrence of a complexion transition.