| Abstract Scope |
(Co,Cu,Mg,Ni,Zn)O is known to exhibit both entropy and enthalpy driven phase transformations that produce a complex, multi-phase microstructure dependent on processing conditions. The formation of the Cu-rich tenorite and Co-rich spinel secondary phases is well studied, but the ability to engineer the crystal structure of the secondary phases through compositional doping has not been explored. In this study, we leverage the capacity of Mn/Co-spinel phases to adopt both cubic and tetragonal crystal structures simultaneously due to the multiple stable valent states of the cations. By adding Mn<sub>3</sub>O<sub>4</sub> to (Co,Cu,Mg,Ni,Zn)O, we are able to engineer the crystal structure of a Mn-rich secondary phase by manipulating post-consolidation heat treatments to investigate the enthalpic nature of Mn-dependent phase transformations. Bulk samples are consolidated using conventional sintering, and then heat treated to produce multi-phase microstructures. X-ray diffraction, scanning election microscopy, and transmission electron microscopy are used to characterize the secondary phases. |