source: University of Houston
Science is taking a step forward in the quest for superconductors that will not require ultra-high pressure to function, thanks to multinational research led by Xiaojia Chen at the University of Houston.
"It has long been superconductivity researchers' goal to ease or even eliminate the critical controls currently required regarding temperature and pressure," said Chen, the M.D. Anderson Professor of Physics at UH's College of Natural Sciences and Mathematics and a principal investigator at the Texas Center for Superconductivity at UH.
The evolution toward eliminating the current special handling now required by superconductive material—which is defined as material that offers little or no impedance from electrical resistance or magnetic fields—hints that the potential for radical boosts in efficiency for certain processes in research, health care, industry, and other commercial enterprises might become reality before long.
But currently, the conditions needed for successful superconductivity outstretch the resources of many potential users, even many research laboratories.
Chen explains that lowering the accessible pressure for superconductivity is one important goal of the current studies on hydrides. "But the experiments are still challenged in providing a set of convincing evidence," he said.
"For example, rare-earth hydrides have been reported to exhibit superconductivity near room temperature. This is based on the observations of two essential characteristics—the zero-resistance state and the Meissner effect," Chen said.
(The Meissner effect, discovered in 1933, recognizes a decrease or reverse in magnetism as a material achieves superconductivity, providing physicists with a method to measure the change.)
"However, these superconducting rare-earth materials performed on target only at extremely high pressures. To make progress, we have to reduce synthesis pressure as low as possible, ideally to atmosphere conditions," Chen explained.
Chen's team found their breakthrough with their choice of conductive media—alloys of hydride, which are lab-made metallic substances that include hydrogen molecules with two electrons. Specifically, they worked with yttrium-cerium hydrides (Y0.5Ce0.5H9) and lanthanum-cerium hydrides (La0.5Ce0.5H10).
The inclusion of Cerium (Ce) was seen to make a key difference.
"These observations were suggested due to the enhanced chemical pre-compression effect through the introduction of the Ce element in these superhydrides," Chen explained.
Two journal articles detail the team's findings. The more recent, in Nature Communications, focuses on yttrium-cerium hydrides; the other, in Journal of Physics: Condensed Matter, concentrates on lanthanum-cerium hydrides.
The team has found these superconductors can maintain relatively high transition temperatures. In other words, the lanthanum-cerium hydrides and yttrium-cerium hydrides are capable of superconductivity in less extreme conditions (at lower pressure but maintaining relatively higher transition temperature) than has been accomplished before.
"This moves us forward in our evolution toward a workable and relatively available superconductive media," Chen said. "We subjected our findings to multiple measurements of the electrical transport, synchrotron X-ray diffraction, Raman scattering, and theoretical calculations. The tests confirmed that our results remain consistent."
"This finding points to a route toward high-temperature superconductivity that can be accessible in many current laboratory settings," Chen explained. The hydride research moves the frontier far beyond the recognized standard set by copper oxides (also known as cuprates).
"We still have a way to go to reach truly ambient conditions. The goal remains to achieve superconductivity at room temperature and in pressure equivalent to our familiar ground-level atmosphere. So the research goes on," Chen said.