This study identifies the crystalline defects commonly observed in conventional yttria ceramics, and proposes a processing route to produce highly densified yttria without the use of sintering aids. The primary objective is to obtain a dense yttria monolith with optimized microstructure and enhanced functional properties. The sintering behavior, mechanical performance, and plasma etching resistance of the yttria specimens were systematically analyzed as a function of the initial powder characteristics. A three-step sintering protocol was employed to suppress abnormal grain growth, yielding fully densified ceramics with uniform and controlled grain size distribution. Calcination of the yttria powder at 1,250 °C for 48 h effectively eliminated oxygen deficiencies and minimized hydration effects. The duration and temperature of each sintering stage significantly influenced grain evolution, which was reflected in the variations in Vickers hardness, Young’s modulus, and fracture toughness (KIC). The resulting yttria ceramics exhibited superior plasma resistance compared with Al2O3, ZrO2, quartz, and Si wafer, demonstrating markedly reduced weight loss during plasma etching. These findings highlight the critical role of proper initial powder treatment and precisely controlled sintering kinetics for achieving yttria monoliths with enhanced densification, mechanical integrity, and plasma erosion resistance. This work provides a practical route for high performance yttria ceramics, offering enhanced densification, structural stability, and the reliability necessary for integration into advanced systems exposed to harsh plasma environments.

The plausibility factors influencing heterogeneous nucleation at the metal/glass interface were systematically investigated as a function of temperature. Secondary phase formation at the metal/glass interface is governed by the contact angle, which is affected by volumetric changes, microstructural evolution driven by metal ion diffusion, and redox reactions influenced by the arrangement of oxygen layers on the metal surface. A comprehensive model was developed to describe these plausibility factors based on observed interfacial phenomena. Despite the inherent non-uniformity in ion distribution within the glass, the interfacial diffusion coefficient, derived from an Arrhenius plot, exhibited a clear temperature dependence, reflecting thermally activated diffusion processes. Above the glass transition temperature (Tg), chemical interactions between diffusing metal ions and migrating glass constituents were identified as the main driving force for secondary phase formation at the metal/glass interface. These chemical reactions not only alter the local stoichiometry but also contribute to structural rearrangements at the interface. The results highlight the complex interplay between the thermal, chemical, and structural factors that control nucleation at the metal/glass boundary. The proposed model provides valuable insight into the mechanisms of interfacial phase formation and offers a useful framework for the design and processing of metal/glass composite systems with tailored properties.