Raising the heat on superconductors
Researchers have used high-energy X-ray powder diffraction to investigate the fundamental science behind the transition of materials into high-temperature superconductors.
By pouring the FeSe into a solution of lithium in liquid ammonia at temperatures between -78 °C and room temperature, the researchers used time-resolved X-ray powder diffraction to investigate how intercalates (layers within the crystalline structure of FeSe) formed. This resulted in the discovery of new crystalline superconductors with Tcs of about 40 Kcontaining large amounts of ammonia between the FeSe layers (see Figure).
Intercalation of Li+ ions and ammonia / NH2- ions into FeSe and the equilibrium between the ammonia-poor and ammonia-rich phases which are both high temperature (Tc ~ 40 K) superconductors. The 2D film plot of powder XRD patterns conducted at I12 (bottom right) and the NH3 adsorption / desorption isotherms (bottom left) accompany the chemical reaction and the equilibrium, respectively.
Setting up the beamline to investigate the reaction proved to be one of the major challenges of the project. "Ammonia is a gas at room temperature, so cooling it to look at the reactions was tricky" explained Stefan Sedlmaier, of Oxford University. "Fortunately, we were able to work with the beamline scientists and the glassblower at Oxford Chemistry to create a special vessel in our labs, which could hold the liquid ammonia safely and allow us to pour in the FeSe powder to initiate the reaction while the solution was exposed to the intense, high-energy X-ray beam on I12."