Influences of TiO₂ or Y₂O₃ doping on the homogeneity of polycrystalline Al₂O₃ produced by pulsed electric current sintering

Influences of TiO2 or Y2O3 dopants on pressure-assisted sintering of polycrystalline Al2O3 were investigated to control the microstructure of sintered Al2O3 as well as to improve the homogeneity of transparent Al2O3 samples. The transparent polycrystalline Al2O3 samples with and without the dopants were fabricated by two-step pulsed electric current sintering (TS-PECS). By the grain boundary segregation by the dopants, both TiO2 and Y2O3 depressed the densification and grain growth processes during the sintering of polycrystalline Al2O3. The principle originalities of this work include the relationship between the homogeneities of microstructure and of optical transmittance of large-size polycrystalline Al2O3 and the consequent doping strategy for controlling of homogeneity of transparent polycrystalline Al2O3 prepared by two-step PECS. Doping of Y2O3 dramatically reduced the grain size of polycrystalline Al2O3 and improved its optical transparency. The homogeneity of the microstructure and the optical transparency of the large-sized polycrystalline Al2O3 with 0.1 mol% Y2O3 was improved. The addition of TiO2 also slightly retarded densification and reduced the grain size of the sintered Al2O3 samples. However, TiO2 dopant is not good for applications of transparent Al2O3 because it caused a dark color in transparent polycrystalline Al2O3 samples by uncertain reasons.