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

Abstract

Influences of TiO 2 or Y 2 O 3 dopants on pressure-assisted sintering of polycrystalline Al 2 O 3 were investigated to control the microstructure of sintered Al 2 O 3 as well as to improve the homogeneity of transparent Al 2 O 3 samples. The transparent polycrystalline Al 2 O 3 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 TiO 2 and Y 2 O 3 depressed the densification and grain growth processes during the sintering of polycrystalline Al 2 O 3 . The principle originalities of this work include the relationship between the homogeneities of microstructure and of optical transmittance of large-size polycrystalline Al 2 O 3 and the consequent doping strategy for controlling of homogeneity of transparent polycrystalline Al 2 O 3 prepared by twostep PECS. Doping of Y 2 O 3 dramatically reduced the grain size of polycrystalline Al 2 O 3 and improved its optical transparency. The homogeneity of the microstructure and the optical transparency of the large-sized polycrystalline Al 2 O 3 with 0.1 mol% Y 2 O 3 was improved. The addition of TiO 2 also slightly retarded densification and reduced the grain size of the sintered Al 2 O 3 samples. However, TiO 2 dopant is not good for applications of transparent Al 2 O 3 because it caused a dark color in transparent polycrystalline Al 2 O 3 samples by uncertain reasons.