Phosphine as a Superconductor?

Phosphine is one of the newest materials to be named a superconductor, a material through which electricity can flow with zero resistance. Scientists first liquefied phosphine in 2015, squeezing it under high pressure in a diamond vise to achieve superconductivity, and now a group of researchers from the University of Buffalo (UB) is providing insight into what may have happened to the chemical as it underwent this intense compression.

The UB scientists say phosphine’s superconductivity under pressure likely arose due to the compound decomposing into other chemical products that contain phosphorus and hydrogen. “So it’s probably a mix of these decomposition products, and not phosphine itself, that results in the superconductivity observed in experiments,” says Eva Zurek, an associate professor of chemistry in the UB College of Arts and Sciences.

The findings could assist scientists in the quest to find or create new commercially feasible superconductors, often sought after because the materials transmit energy with ultra-high efficiency, losing no energy and giving off no heat, according to Zurek. “In experiments where high pressures are involved, it’s difficult for scientists to characterize what materials they’ve created,” Zurek says. “But understanding what’s actually there is important because it gives us an idea of how we might go about making new superconducting compounds.”

The new study was published in the Journal of the American Chemical Society as a “Just Accepted Manuscript” and will appear in a future print edition of the journal.

At room temperature, phosphine is composed of one atom of phosphorus (P) and three of hydrogen (H). UB researchers calculated that under pressure, PH3 becomes unstable and likely breaks down into more stable structures that include PH2, PH and PH5.

Zurek’s team used XtalOpt, an open-source computer program that one of her former students created, to understand which combinations of phosphorus and hydrogen were stable at pressures of up to 200 gigapascals—nearly two million times the pressure of our atmosphere here on Earth, and similar to the pressure at which phosphine was squeezed in the diamond vice in the superconductor experiment.

One reason researchers are so keen on finding new superconductors is that the only known superconductors are superconducting only at extremely low temperatures.

Interest in the field has intensified over the past year after a team led by scientist Mikhail Eremets smashed previous temperature records by finding a hydrogen and sulfur compound, squeezed under 150 gigapascals of pressure, was a superconductor at 203K, about -94ºF.

Eremets and his colleagues were also the group that conducted the experiment on phosphine, with superconductivity observed at temperatures higher than 100K (roughly -280ºF). “Finding materials that are superconducting at high temperatures would revolutionize our electric power infrastructure, because virtually no energy would be wasted during transmission and distribution through superconducting wires,” Zurek says. “In addition, superconducting magnets could be employed for high-speed levitating trains (maglev) that move more smoothly and efficiently than wheeled trains. These technologies exist nowadays, but the superconductors must be cooled to very low temperatures for them to work.”