Investigation of annealed and metamict pyrochlore minerals by x-ray absorption spectroscopy. [Synthetic pyrochlores with general formula (RE)/sub 2/Ti/sub 2/O/sub 7/, RE = Er, Y/sub 2/, Gd/sub 2/, Dy, La]

Abstract

Materials of the pyrochlore structure type exhibit a variety of interesting properties including phases capable of acting as hosts for actinides in radioactive wastes. Studies of curium doped gadolinium titanate phases (Gd/sub 2/Ti/sub 2/O/sub 7/) have been made which showed that the radiation damage ingrowth followed an exponential relationship. For the study reported here a series of synthetic pyrochlores were produced having the titanate phase with the general formula (RE)/sub 2/Ti/sub 2/O/sub 7/, RE = Er, Y/sub 2/, Gd/sub 2/, Dy, La. Additionally a set of metamict (radiation damaged) pyrochlores was examined in both a natural and post temperature annealed state. Experiments were conducted on these samples using the Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) techniques. In summary, these studies show that in pyrochlore structure types the Ti-O cage undergoes changes due to radiation damage. The individual Ti-O bonds become more disordered which leads to a loss of short and long range order and, ultimately, to expansion of the bulk material. 2 refs., 2 figs