Microstructural and spectroscopic analysis in non-uniform Y₂O₃ ceramics fabricated by spark plasma sintering

In Y₂O₃ ceramics densified at 1000 °C by spark plasma sintering (SPS), non-uniform sintering behavior of grains and pores occurred for a heating rate of 20 °C/min. The sintered Y₂O₃ was translucent at the periphery but white and opaque at the center. According to microstructural analysis, the non-uniform sintering was caused by rapid grain growth and pore coarsening at the center. Under complicated electric and magnetic fields during SPS, an assumption of the movement of defects toward the center enables to explain the microstructural non-uniformity. For the non-uniform sintering behavior, spectroscopic analysis was used to investigate the introduced impurities (C, H, O) and by-products (carbonates). In the spectroscopic analysis, the peaks located at 2555, 2950, and 3560 cm¹¹ (OH stretching band of H₂O) were weakly detected for low heating rates but clearly detected for high heating rates. This is because H₂O adsorbed to the initial Y₂O₃ powder was not sufficiently removed and was trapped during rapid densification at high heating rates. Due to the carbon-rich environment during SPS, carbonate was formed by the reaction of carbon with OH. Most carbons were detected as a CO peak, indicating that a reaction of carbon with OH occurred.