The team, including former ANU PhD scholar Tom Shiell now at Carnegie Institution for Science, previously created Lonsdaleite in the lab only at high temperatures.
This new unexpected discovery shows both Lonsdaleite and regular diamond can also form at normal room temperatures by just applying high pressures — equivalent to 640 African elephants on the tip of a ballet shoe.
“The twist in the story is how we apply the pressure. As well as very high pressures, we allow the carbon to also experience something called ‘shear’ — which is like a twisting or sliding force. We think this allows the carbon atoms to move into place and form Lonsdaleite and regular diamond,” Professor Bradby said.
Co-lead researcher Professor Dougal McCulloch and his team at RMIT used advanced electron microscopy techniques to capture solid and intact slices from the experimental samples to create snapshots of how the two types of diamonds formed.
“Our pictures showed that the regular diamonds only form in the middle of these Lonsdaleite veins under this new method developed by our cross-institutional team,” Professor McCulloch said.
“Seeing these little ‘rivers’ of Lonsdaleite and regular diamond for the first time was just amazing and really helps us understand how they might form.”
Lonsdaleite, named after the crystallographer Dame Kathleen Lonsdale, the first woman elected as a Fellow to the Royal Society, has a different crystal structure to regular diamond. It is predicted to be 58 percent harder.
“Lonsdaleite has the potential to be used for cutting through ultra-solid materials on mining sites,” Professor Bradby said.
“Creating more of this rare but super useful diamond is the long-term aim of this work.”
Ms. Xingshuo Huang is an ANU PhD scholar working in Professor Bradby’s lab.
“Being able to make two types of diamonds at room temperature was exciting to achieve for the first time in our lab,” Ms. Huang said.
The team, which involved University of Sydney and Oak Ridge National Laboratory in the US, have published the research findings in the journal Small.
Reference: “Investigation of Room Temperature Formation of the Ultra‐Hard Nanocarbons Diamond and Lonsdaleite” by Dougal G. McCulloch, Sherman Wong, Thomas B. Shiell, Bianca Haberl, Brenton A. Cook, Xingshuo Huang, Reinhard Boehler, David R. McKenzie and Jodie E. Bradby, 2020 Nov 04, Small.