Influence of grain growth on the structural properties of the nanocrystalline Gd2Ti2O7

The microstructural evolution and grain growth kinetics of the nanocrystalline Gd2Ti2O7 drastically affect its properties and functionalities as thermal barrier coatings and nuclear waste forms for actinide incorporation. Here, we report the synthesis of the dense nano-sized Gd2Ti2O7 by high energy ball milling (HEBM), and spark plasma sintering (SPS), and also investigated the isothermally annealing induced grain coarsening and structural properties variations. As-prepared nano powder (D similar to 60 nm) by HEBM exhibited an amorphous nature, which was consolidated to a dense single phase crystalline pyrochlore nano-ceramic (D similar to 120 +/- 10 nm) by SPS sintering at 1200 degrees C. Isothermal annealing was performed at different temperatures (1300 degrees C - 1500 degrees C) with holding time varying from 0.5 to 8 h, and the pyrochlore phase is stable with no indication of a transformation into a defect fluorite structure. A rapid initial grain growth was observed which increased with temperature and annealing durations due to the large driving force of the curvature-driven grain coarsening of the nano-ceramics, and grain growth saturates at longer durations. The calculated value of the time constant and activation energy for the nanocrystalline Gd2Ti2O7 were 0.52 +/- 0.02 and 240 +/- 20 kJ/mol (similar to 2.48 eV), respectively. The enhanced grain growth kinetics with a lower value of activation energy can be explained by the effect of fast diffusion across the grain boundaries for dense nanoceramics. (C) 2017 Elsevier B.V. All rights reserved.