Al2O3–SiO2–ZrO2 ternary glasses were fabricated using a levitation technique. The addition of ZrO2 to the Al2O3–SiO2 glasses strongly affected their thermal, mechanical, and structural properties. Several compositions were partially vitrified at the laser-melted area without levitation although their melting required temperatures higher than 2000°C. With increasing ZrO2 content, the elastic moduli linearly increased, and the 50Al2O3–20SiO2–30ZrO2 glass exhibited a Young′s modulus of 166 GPa and Vickers hardness HV of 11 GPa. Conversely, crack resistance significantly decreased with the addition of ZrO2. Density measurements, Zr L2,3-edge and K-edge X-ray absorption fine structure analyses, and 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy were performed to investigate the local structure around Zr, Al, and Si in the glasses. Zr formed distorted ZrO7 as in monoclinic ZrO2, which has been rarely found in conventional oxide glasses. The highly oxygen-coordinated Al atoms such as AlO5 and AlO6, were the main components in the glasses rather than AlO4. The majority of Si atoms form SiO4 with four bridging oxygen (Q4). Among the four bridging oxygens, the number of oxygens connected to Al or Zr clearly increased with decreasing SiO2 content. The high packing density of the ternary glasses that resulted in high elastic moduli originated from the highly oxygen-coordinated Zr and Al and their close bonding with SiO4 without generating nonbridging oxygens.
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