Microstructure evolution of gadolinium doped cerium oxide under large thermal gradients

The effects of large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were investigated. GDC powder was prepared by solvent deficient method and sintered at 1650 degrees C for 10 h to achieve dense ceramics with -8 mu m grain size. The densified GDC samples were subsequently annealed using a 60 W infrared laser at over 2100 degrees C for 1 h under a thermal gradient equivalent to -0.3-0.5 degrees C/mu m. The postannealed samples at 2150 degrees C for 1 h exhibit grains with average length and width of 37 and 28 mu m, respectively. Electron backscattered diffraction (EBSD) analysis revealed that the post-annealed sample at 2150 degrees C consists of grains oriented close to five principal directions ( 4 3 10 0 0 1 13 1 14 7 6 20 7 2 7 on [0 1 0]) within a tolerance angle of +/- 10 degrees, whereas the grains of the pre-annealed sample are randomly oriented. Gadolinium diffuses 20-30 mu m away from the irradiated surface, with the measured composition of regions deeper than 30 mu m, Ce0.86Gd0.14O1.93, is close to that of the pre-annealed sample, Ce0.87Gd0.13O1.94. Enhancement of total conductivity of the post-annealed GDC (1.1 x 10-3 S cm-1 at 500 degrees C, and 2.1 x 10-2 S cm-1 at 700 degrees C) is observed when compared to the pre-annealed GDC (3.1 x 10-5 S cm-1 at 500 degrees C, and 1.7 x 10-3 S cm-1 at 700 degrees C), and points to the decrease in the grain boundary (GB) resistivity. This could be attributed to both the change in GB area and grain alignment.

Automated summary

The effects of large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were studied, showing changes in grain orientation, gadolinium diffusion, and enhancement of total conductivity after annealing.