Synthesis and Structural Analysis of Four Y-Ti-O Oxide Phases Prepared by Solid-State Reaction

The nature of oxide nanoparticles in oxide dispersion strengthened (ODS) steels has been unclear because of their nanoscale geometry. To provide model materials for understanding these oxide nanoparticles, bulk Y-Ti-O ceramics were synthesized via solid-state reaction above 1200°C. Composition-dependent phase evolution from defect-fluorite Y2TiO5 to ordered pyrochlore Y2Ti2O7 across the compositions ranging from TiO2:Y2O3 = 1:1 to 2:1 was identified by X-ray diffraction and transmission electron microscopy, with structural modulations detected in defect-fluorite Y2TiO5. The TiO2:Y2O3 = 1:1 composition exhibited polymorphs, namely defect-fluorite Y2TiO5, hexagonal β-Y2TiO5, and orthorhombic α-Y2TiO5, corresponding to high-, intermediate-, and low-temperature phases, respectively. The representative structural models of those phases were constructed based on diffraction observations, reported space-group information, and crystallographic considerations. Observed phase behaviors differed from previously reported phase relations in the Y2O3-TiO2 system.