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In this study, 10 wt.% ceramics—Al₂O₃, La₂O₃, Y₂O₃, MgO, and TiO₂—were employed as additives for amorphous SiO₂ after pressing and annealing at 1300 °C. The amorphous SiO₂ changed to cristobalite SiO₂. Through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy with energy-dispersive spectrometry, the reaction phases of La₂Si₂O₇, Y₂Si₂O₇, and MgSiO₃ (Mg₂SiO₄) were found in the SiO₂ with 10 wt.% La₂O₃, Y₂O₃, and MgO additives. Cracks formed in the Si and SiO₂–ceramic additive sites because of the difference in the coefficients of thermal expansion among the Si, SiO₂, ceramic additives, and reaction phases. After Si came into contact with the SiO₂–ceramics, two types of microstructures were found: those with and those without an amorphous SiO₂ reaction layer at the interface. Amorphous SiO₂ layer formation is due to the replacement of the Si position in SiO₂ by Al³⁺ and Ti⁴⁺ impurities, which can break the bonds between Si atoms. The O content in the Si decreased from 6–9 × 10¹⁷ atoms/cm³ for SiO₂ to less than ~10¹⁶ for SiO₂–Al₂O₃ and SiO₂–MgO. The average resistivity of the Si was 3 Ω·cm for SiO₂ and decreased to 0.12–0.36 Ω·cm for the SiO₂ with ceramic additives.