Annealing of Pyroclores and XRD Characterization

The next step was to anneal the pyrochlores. Combustion synthesis is a relatively simple method of creating the pyrochlores however during the combustion, carbon impurities enter the sample showing up as black and grey specks in the powder sample. This "dirty" look to the powders immediately after combustion synthesis is shown in the first picture. In addition, the process leaves the crystalline structure of the powders heterogeneous and sometimes incompletely formed. The process of annealing in which the powders are heated in crucibles at 1200 degrees Celsius for 2 hours removes the impurities in the pyrochlores and improves their crystallinity.

Half the mass of each pyrochlore was placed in a crucible and set in the furnace shown in the second picture. The furnace was set to 1200 degrees Celsius and allowed to run for 2 hours. The powders were then allowed to cool outside the furnace and stored in separate vials. The appearance of the powders after the annealing process can be seen in the third picture. The carbon impurities evaporate away at such high temperatures making the powders appear much cleaner and uniform in color.

The powders were then characterized using an XRD or X-Ray Diffractor which is shown in the fourth picture. The XRD hits a small sample of a powder with an X-ray and measures the scattered intensity of the X-ray. The intensity measured is plotted against the respective angle of measurement for that intensity. This creates a graph that can be compared to standardized graphs maintained by the International Center for Diffraction Data (ICDD) to make sure the powder formed is what was expected. The confirmed diffraction pattern from the ICDD for a certain chemical (i.e. La2Zr2O7 in one case) is laid over the diffraction pattern being created from the powder sample in the XRD. If the relative intensities and locations of peaks match up properly, it is confirmed that the sample synthesized is what it was expected to be. The XRD characterization showed that all of the pyrochlores had been properly synthesized and were ready for spectroscopic characterization at Oak Ridge National Laboratory.