Impact of oxygen vacancies on the thermophysical properties of the phase‐pure Mg₂TiO₄ ceramics

Abstract Phase‐pure, highly dense (∼97%) magnesium orthotitanate (Mg 2 TiO 4 ) ceramics were processed via two distinct pressureless sintering techniques, e.g., conventional sintering in air and vacuum sintering in a hot press unit. The conventionally sintered Mg 2 TiO 4 ceramic (CS) exhibited the highest thermal conductivity value of , reported to date. In contrast, vacuum sintered Mg 2 TiO 4 ceramic (VS) demonstrated a comparatively lower thermal conductivity value of . The measured coefficient of thermal expansion (CTE) for CS and VS at 1683 K was and , respectively. A phonon‐lattice softening mechanism, likely driven by a higher concentration of oxygen vacancies, had a strong influence on the VS sample. In inverse spinel‐based systems, computational studies have previously predicted an order‐disorder phase transition occurring beyond 800°C. This transition is strongly associated with anharmonic phonon scattering processes. In the present work, we provide the first experimental validation of these predictions. Although oxygen vacancy is generally considered a favourable factor for numerous functional applications, it adds no benefit in relation to the thermophysical properties (i.e., thermal conductivity and thermal expansion) of the Mg 2 TiO 4 ceramics. VS and CS showed minimal MgO after repeated quenching in 5°C water. While annealing post‐quenching induced clear phase separation of MgO, MgTiO 3 , and Mg 2 TiO 4 .