Pyrochlore to fluorite transitions - ordering in fluorites?
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Materials Research Society
Two systems have been studied La2-xYxZr2O7 and La2-xYxHf2O7, as part of an on-going study of radiation tolerance in nuclear waste forms and related oxide materials. The structural effects of increasing Y content in La based zirconate and hafnate pyrochlores have been studied with neutron diffraction and electron microscopy. Results have shown a difference in structural stability for both the pyrochlore and fluorite phases within each system, including the presence of two-phase regions in both systems. In the zirconate, the two-phase region lies in the range x = 0.9-1.6. This is shifted to higher Y content in the hafnate system and lies in the range of x = 1.5 to approximately 1.8-1.9. In addition to the differences in phase stability, electron diffraction, predominantly down the  zone axis, has shown evidence for ordering in the form of structured diffuse scattering within the fluorite phases.
Pyrochlore, Fluorite, Neutron diffraction, Electron microscopy, Diffuse scattering, Hafnates
Whittle, K. R., Cranswick, L. M., Redfern, S. A. T., Swainson, I. P., & Lumpkin, G. R. (2008). Pyrochlore to fluorite transitions - ordering in fluorites? Paper presented to the 2008 MRS Fall Meeting, 1st – 5th December 2008. Boston, Massachusetts, United States of America: Hynes Convention Center. In K. E. Sickafus, A. Navrotsky, S. R. Phillpot (Eds.), MRS Proceedings: Structure/Property Relationships in Fluorite-Derivative Compounds, 1122, 66-71. doi:10.1557/PROC-1122-O03-01