Highly transparent zinc aluminate ceramics were fabricated by the solid-state reaction using a spark plasma sintering machine. The sintered body exhibited a microstructure consisting of submicron-sized grains and extremely low porosities. Annealing of the sintered body in air improved the transmission close to the theoretical limit in a wavelength range of 15¯m. The band gap energy estimated from the absorption coefficient was 4.3 eV. The Young's modulus and the bulk modulus measured for the fully dense zinc aluminates were 282 and 211 GPa, respectively.

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Zinc oxide (ZnO) thermoelectric ceramics were consolidated by spark plasma sintering (SPS) along with onestep/two-step sintering (OS/TS) temperature profiles, the latter employing a strategy of heating to a higher temperature (T 1 ) followed by prolonged sintering at a lower temperature (T 2 ) for densification while preventing grain growth. In the first step, the temperatures and holding times were 1100 and 1150 °C for 15 and 5 min, respectively, and the second-step was maintained at 1050 °C for 30, 60, and 120 min. By combining TS and SPS processes (TS-SPS), high relative densities of 91.494.9 % were achieved without significant grain growth. Electron backscatter diffraction (EBSD) revealed a noticeable grain-growth suppression of 56 % for the TS-SPS sample with T 1 = 1100 °C. The highest power factor of 7.8 © 10 ¹5 W K ¹2 m ¹1 was achieved for the TS-SPS ZnO, while the lowest thermal conductivity of 4.7 W K ¹1 m ¹1 was achieved for the OS-SPS ZnO, attaining a figure of merit (ZT) of 0.017 at 775 °C.