Hidden mechanics paper

I’ve just had a new paper accepted! It’s a result of an exciting new collaboration with Stephen Moggach at Edinburgh University, who’s an expert on science under extreme conditions. We studied crystals of a coordination polymer, lithium l-tartrate (polymorph number 9, for anyone following my previous papers), when subjected to pressures up to 5.5 gigapascals – the equivalent of 2 Statue of Liberty’s standing on 1 stiletto heel…

Ambient pressure structure of lithium tartrate polymorph 9

Most materials, when subjected to pressure from all sides, get smaller. While most materials do this more in some directions than others, there are a few exceptional cases in which the material actually expands in one direction. This is the phenomenon called “negative linear compressibility”, NLC. It’s generally a result the material’s structure: think about a collapsing wine rack and you’ll see how, when one direction is squeezed, the other has to expand. Materials with wine rack structures tend to exhibit NLC most at ambient pressure and the effect tails off gradually.

Using in-situ high-pressure single crystal synchrotron X-ray diffraction at Diamond Beamline I19, we have found that lithium l-tartrate exhibits NLC comparable to many of the most exceptional materials to date. What is unusual – and confirmed by variable temperature studies and DFT calculations – is that the NLC response is absent at ambient pressure: it only becomes active above 2 gigapascals.

By looking at the structure in more detail, we could explain this strange behaviour by the interplay between compression of the struts and opening of the “wine rack angle”, which gives us this rare example of “hidden” negative linear compressibility. This sort of property could be useful in new types of sensors, switches or even artificial muscles! The paper is published in the journal Physical Chemistry Chemical Physics, here. I’m looking forward to investigating more of this in the future…


Thanks Rebecca, Claire, Scott, Stephen, Tony and Dave for all your hard work and patience!


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