Engineers at the University of Cambridge used new techniques to manufacture high-temperature superconducting materials, producing samples that can carry record quantities of electrical current for their type and size. The Cambridge team have developed a technique to manufacture large single grains of bulk superconductors.
The breakthrough has improved the effectiveness of yttrium barium copper oxide (YBCO) and a related family of superconducting materials. It raises the prospect of more powerful and affordable samples that could have huge benefits in a number of fields.
In the past, however, producing effective bulk superconducting devices from the material has proved difficult. YBCO is processed most easily in the form of a polycrystalline ceramic, but has to be manufactured as a single grain in order to generate large magnetic fields since boundaries between grains limit the flow of current in the bulk sample.
In addition, microscopic defects within the material can impede, or ‘pin’ the motion of magnetic flux lines and increase the flow of current through it. The distribution of these lines within a bulk superconductor has to be managed to maximise the flow of current and therefore the field.
The Cambridge team have developed a technique to manufacture large single grains of bulk superconductors that involves initially heating the material to a temperature of 1,000 degrees C, causing it to part-melt. In a series of experiments, various elements, such as depleted uranium, were then added to the chemical composition of the superconductor to generate artificial flux pinning sites within the single grain.
When the material cooled and reformed, these added materials retained their integrity and formed physical obstacles that form direct the motion of magnetic flux lines, enabling larger currents to flow.
In addition, the team developed a technique for fabricating large, single grains of bulk superconductors in air, using a new type of seed crystal that they have also patented, which enables much more scope for optimising the partial-melt process. Together, these techniques led to the production of samples far more powerful than those fabricated by more standard techniques, which exhibited record energy densities and magnetic fields for their size.
“The properties these samples exhibit could in time offer huge commercial potential by improving or reducing the weight and size of applications such as energy storage flywheels, magnetic separators, motors and generators,” Professor Cardwell added. “These devices already use superconductors to varying degrees. With these new bulk processing techniques, we could greatly improve their power and potential.”