A research team at PNNL has identified reasons why certain materials may be able to survive rough-and-tumble environments and still maintain their functionality. The findings could be key to making more reliable space-based electronics, nuclear power plant sensors, and nuclear waste forms.
The team’s research, funded through PNNL’s Nuclear Process Science Initiative (NPSI), focused on understanding the evolution of a special class of materials called pyrochlore oxides in extreme radiation environments. Pyrochlores have long been studied for radiation-related applications, but it has not been clear how the material’s basic framework, the crystal lattice, responds to different types of radiation damage.
The team investigated the material’s behavior using advanced computer simulations that allowed them to access fast structural distortions at the atomic level that can’t be measured with high accuracy in laboratory experiments. The study revealed how the crystal lattice deforms under irradiation, eventually leading to complete loss of order through a process called amorphization.
“Our first principles simulations allowed us to identify the distortions in the materials, effectively opening a window into processes that occur at length and time scales that are difficult to access experimentally,” says Michel Sassi, a PNNL materials scientist. Sassi served as lead author on a paper chronicling the results. The paper was published recently in Scientific Reports.
Chemistry Versus Structure
To discover more about this response, the researchers explored pyrochlores with two different lattice types: cubic (cube-shaped cells) and monoclinic (rectangular prisms with one of the angles being different to 90°). The team’s simulations examined electronic damage processes and calculated the materials’ response to electronic excitations.
The researchers found that the crystal structure of the lattice influences the kind of distortions that can be incurred during the damage process. In the cubic case, the atomic arrangements are such that structural distortions are constrained, making damage generation difficult. However, the monoclinic lattice can easily undergo structural deformations, by means of octahedral rotations, allowing the crystal to accommodate radiation damage with more flexibility, but also speeding up the amorphization process.
Importantly, the team also found that the chemical composition of the material influences its radiation resistance; by choosing different elements to put into the structure, the response can be tuned to make the material more or less radiation-resistant. These findings are important because they illustrate how the “competition” between pyrochlore chemistry and structure control the material’s dynamic response to radiation damage.
Next step is microscopy
The results of this study will help guide future experimental work, and potentially inform the selection of better materials for use in extreme radiation environments. The team is currently conducting microscopy to compare to numerical simulations, with the ultimate goal to make these materials more radiation resilient for a range of applications.
The study was conducted as part of the NPSI project, “Damage Mechanisms and Defect Formation in Irradiated Model Systems,” led by PNNL materials scientist Steven Spurgeon.
NPSI is a five-year, internally funded research effort focused on understanding, harnessing, and exploiting the interfacial phenomena controlling the behavior of materials in nuclear processing.