Irradiation effects in ceramics for nuclear waste storage

Nan Jiang, Arizona State University, DMR 0603993

The successful development of materials suitable for safe nuclear waste storage requires novel strategies for controlling materials under radiation at the nanoscale or even the atomic level. Historically, radiation effects have been studied by relying on measurements of the end-products of the damage processes. Due to the complexity of radiation effects, such post-radiation observations cannot reveal the initial process of radiation damage, and so have caused confusion as to the fundamental mechanisms of damage in ceramics and glasses. We have developed a procedure to detect the early stages of radiation damage in nuclear waste glasses and ceramics using in situ electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM). This nanoscale spectroscopy offers an unprecedented combination of spatial, time and energy resolution for direct observation of the initial stages of the damage process. An example is given in the study of radiation damage in Zircon (ZrSiO4), which has been extensively studied for the use for immobilization of plutonium. Our results overturn the previous suggestions of amorphization of zircon under high-energy electron irradiation. The damage is mainly cause by the preferential sputtering of O. The loss of O does not uniformly occur within the illuminated area, but rather within small sporadic regions. These isolated patches gradually connect each other. The damage does not result in forming amorphous zircon, but rather forming nanocrystalline ZrxSiy.

0

0.5

1

10 20 30 40 50

ACDFGJ

Inte

nsit

y

Energy loss (eV)

25.0eV

18.0eV

Zr N-edge

0

1

2

3

4

100 120 140 160 180 200

Inte

nsit

y

Energy loss (eV)

Si L23

Si L1

Zr M45

B

E

H

K

In situ HREM images and SAED patterns of zircon showing the damage process induced by electron irradiation

In situ EELS of zircon showing the damage process induced by electron irradiation. The letters represent the recording sequence of each spectrum. Spectra A and B were from undamaged zircon, while spectra J and K from damaged zircon.

International collaboration on photoluminescent materials

Nan Jiang, Arizona State University, DMR 0603993

We hosted an exchange scholar supported by the NSF International Materials Institute (IMI) for New Functionality in Glass (DMR-0409588). The project was “preparation and characterization of novel glass-ceramics with ultra-broadband near-infrared luminescence”. Specifically, we were focusing on developing a cheap and efficient luminescent materials for solar cells. Although solar power is in rapid growth mode, the solar cells are predicted to only supply about 5% of the huge amount of carbon-free energy we will need by 2050. One of reasons is that the newly developed solar cells are too expensive. Our approach is to reconsider our philosophy in the past. We need to build new technologies as simple as possible; not by sacrificing the advanced properties, but by utilizing an inexpensive synthetic method. We proposed a new strategy to realize the broadband spectral modulation. By utilizing a designed hybrid structure of LiYbO2 nanoparticles embedded wide band gap semiconductor ZnO, the high efficient energy transfer from ZnO substrate to Yb3+ ions can be achieved.

This SEM image shows an embedded LiYbO2 nanoparticle in ZnO substrate.

Excitation and emission spectra for (a): 1 mol% Yb2O3 mixed ZnO, λem=498 nm (black), λem=980 nm (red), and λex=380 nm (blue); (b) 1 mol%Li2CO3-1 mol% Yb2O3 mixed ZnO, λem=542 nm (black), λem=980 nm (red), and λex= 397 nm (blue); (c): pure ZnO (orange) and 1 mol% Li2CO3 mixed ZnO (green), λem=498 nm, λex=390 and 365 nm, respectively.