Low temperature synthesis of nanocrystalline Y<inf>2</inf>Ti<inf>2</inf>O<inf>7,</inf> Y<inf>2</inf>Zr<inf>2</inf>O<inf>7,</inf> Y<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> with exceptional hardness by reverse co-precipitation technique

Y2Ti2O7, Y2Zr2O7, Y2Hf2O7 have pyrochlore structure and are found to be promising dispersoids for steel-based oxide dispersed strengthened (ODS) alloys, which are used in nuclear reactor and supercritical boilers applications. They should be nanocrystalline and possess high strength for better performance of ODS alloys. In the present study, oxides are successfully synthesized through Mechanically Activated Annealing (MAA) and Reverse Co-precipitation (RCP) techniques. The RCP technique could yield pyrochlore phase at lower temperatures with finer crystalline size. The structural analysis was done through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectra to confirm the presence of single phase and nanocrystallinity of oxides. Raman spectra probes into local disorderness in the structure and bond length. Y2Hf2O7 synthesized through MAA has the highest hardness (20 GPA) among all the oxides synthesized in the present study and those reported so far. Further, Y2Ti2O7 has higher Young's modulus than the Y2Zr2O7, Y2Hf2O7 due to the orderness in the structure.