Microstructures of TiO2-doped α-Al2O 3 ceramics used as electrostatic chucks (ESC) were investigated by transmission electron microscopy including energy-dispersive spectrometry (EDS) and electron energy loss spectroscopy (EELS) analyses in connection with their electrical properties. The lattice parameters of sintered Al2O 3 grains are almost independent of TiO2 content as well as the sintering temperature, indicating immiscibility of the additive with Al2O3. Scanning transmission electron microscopy (STEM)-EDS revealed that the grain boundaries of α-Al2O 3 are slightly enriched with Ti. It was shown in EELS that the segregated Ti is in a partially reduced state. The Ti-enriched grain boundaries, therefore, play a role as a conductive network, which is responsible for considerable improvement of electronic conductivity with TiO2 doping. STEM-EDS and electron diffraction analyses confirmed that micrometre-sized TiO2 particles are dispersed in the α-Al2O 3 when sintering is operated at 1300°C or lower, while the particles transform into Al2TiO5 at higher temperature. EELS revealed that the TiO2 grains are partially reduced into non-stoichiometric TiO2-y, while Al2TiO5 grains are in the fully oxidized state. The TiO2-y-dispersed α-Al2O3 shows no dielectric relaxation and quite smooth dissipation of the electrostatic condensed charges. In contrast, α-Al2O3 with Al2TiO5 grains possesses pronounced dielectric relaxation, and the electrostatic dissipation takes such a longer time as 30 s. The former is preferable to application to ESC in terms of quick response.
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