NSUF 20-3008: Recrystallization Behavior in Irradiated Gadolinium Titanate as a Proxy for Structural Disorder
In our currently active NSUF RTE proposal, we have been studying the radiation tolerance of nanoporous gadolinium titanate relative to polycrystalline and single crystal microstructures. This work has revealed that the microstructural features, specifically the high density of defect sinks in the nanoporous microstructure are effective in delaying the onset of irradiation induced amorphization relative to the other microstructural configurations. This work will be completed and ready for publication following our February 2020 instrument time. During the course of this set of experiments, we observed an unexpected phenomenon, specifically we found that repeated irradiation induced amorphization and recrystallization cycles led to a systematic increase in the recrystallization temperature. Within these limited observations there was no apparent impact on the amorphization threshold, regardless of the microstructural region (nanoporous or dense polycrystalline) or irradiation temperature. While there are many studies available in the literature that explore irradiation induced amorphization behavior, especially in the case of pyrochlore-based ceramics, these studies are exclusively limited to single irradiation events. There are limited opportunities for repeated recrystallization in practical applications such as nuclear waste containment/isolation; however, systematic investigation of this phenomenon has the potential to shed light on elusive underlying mechanisms that are relevant to predicting the long-term radiation tolerance of these and other ceramic/geological waste form strategies. For example, we hypothesize that the observed phenomenon is fundamentally related to residual defect build-up that is not fully recovered during heat treatments. This would then provide us with a direct, experimental route to systematically probe the impact of residual defect concentration on the evolution of these pyrochlores subject to irradiation. The proposed experimental approach will employ similar in situ irradiation and heating as was employed for our previous efforts. We will also rely upon two specimen configurations. FIB prepared single crystal specimens will serve as a pristine baseline, with limited intrinsic defect sinks. While, “3-zone” pyrochlore specimens, including a single crystal, nanoporous and polycrystalline region, will allow us to establish different levels of amorphiziation in the same specimen. For example, because we have already shown that the nanoporous region has a higher amorphization fluence threshold, we can stop the irradiation process at the point where the polycrystalline region is amorphized but the other regions are simply disordered. This type of 3-zone specimen also inherently contains differing site densities for nucleation during the recrystallization process. Nanobeam diffraction during irradiation and recrystallization heat treatments will be critical to assess the level of disorder and recovery. While video capture and image analysis will enable precise analysis of the thermal-spatiotemporal evolution of the material during heat treatment. The observations enabled by this study have the potential to impact the current understanding of defect evolution and tolerance of pyrochlore systems, possibly elucidating new pathways for improved radiation tolerance.
Additional Info
| Field | Value |
|---|---|
| Abstract | In our currently active NSUF RTE proposal, we have been studying the radiation tolerance of nanoporous gadolinium titanate relative to polycrystalline and single crystal microstructures. This work has revealed that the microstructural features, specifically the high density of defect sinks in the nanoporous microstructure are effective in delaying the onset of irradiation induced amorphization relative to the other microstructural configurations. This work will be completed and ready for publication following our February 2020 instrument time. During the course of this set of experiments, we observed an unexpected phenomenon, specifically we found that repeated irradiation induced amorphization and recrystallization cycles led to a systematic increase in the recrystallization temperature. Within these limited observations there was no apparent impact on the amorphization threshold, regardless of the microstructural region (nanoporous or dense polycrystalline) or irradiation temperature. While there are many studies available in the literature that explore irradiation induced amorphization behavior, especially in the case of pyrochlore-based ceramics, these studies are exclusively limited to single irradiation events. There are limited opportunities for repeated recrystallization in practical applications such as nuclear waste containment/isolation; however, systematic investigation of this phenomenon has the potential to shed light on elusive underlying mechanisms that are relevant to predicting the long-term radiation tolerance of these and other ceramic/geological waste form strategies. For example, we hypothesize that the observed phenomenon is fundamentally related to residual defect build-up that is not fully recovered during heat treatments. This would then provide us with a direct, experimental route to systematically probe the impact of residual defect concentration on the evolution of these pyrochlores subject to irradiation. The proposed experimental approach will employ similar in situ irradiation and heating as was employed for our previous efforts. We will also rely upon two specimen configurations. FIB prepared single crystal specimens will serve as a pristine baseline, with limited intrinsic defect sinks. While, “3-zone” pyrochlore specimens, including a single crystal, nanoporous and polycrystalline region, will allow us to establish different levels of amorphiziation in the same specimen. For example, because we have already shown that the nanoporous region has a higher amorphization fluence threshold, we can stop the irradiation process at the point where the polycrystalline region is amorphized but the other regions are simply disordered. This type of 3-zone specimen also inherently contains differing site densities for nucleation during the recrystallization process. Nanobeam diffraction during irradiation and recrystallization heat treatments will be critical to assess the level of disorder and recovery. While video capture and image analysis will enable precise analysis of the thermal-spatiotemporal evolution of the material during heat treatment. The observations enabled by this study have the potential to impact the current understanding of defect evolution and tolerance of pyrochlore systems, possibly elucidating new pathways for improved radiation tolerance. |
| Award Announced Date | 2020-02-05T14:18:03.833 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | Intermediate Voltage Electron Microscopy (IVEM)-Tandem Facility |
| PI | Jessica Krogstad |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 3008 |