16-Sep-2020 - Max-Planck-Institut für Chemie

On the road to conductors of the future

Superconductivity in hydrogen sulfide

Superconducting wires can transport electricity without loss. This would allow for less power production, reducing both costs and greenhouse gasses. Unfortunately, extensive cooling stands in the way, because existing superconductors only lose their resistance at extremely low temperatures. In the journal Angewandte Chemie, scientist have now introduced new findings about hydrogen sulfide in the H(3)S form, and its deuterium analogue D(3)S, which become superconducting at the relatively high temperatures of -77 and -107 °C, respectively.

This is even true in comparison with the current front-runners, copper-containing ceramics with transition temperatures that start at about -135 °C. Despite extensive research into sulfur/hydrogen systems, many important questions remain. Most importantly, superconducting hydrogen sulfide was previously produced from "normal" hydrogen sulfide, H(2)S, which was converted into a metal-like state with a composition of H(3)S under pressures of about 150 GPa (1.5 million bar). Such samples were inevitably contaminated by hydrogen-depleted impurities that can distort experimental results. To avoid this, researchers led by Vasily S. Minkov have now produced stoichiometric H(3)S by heating elemental sulfur directly with an excess of hydrogen (H(2)) with a laser, under pressure. They also produced samples made with deuterium (D(2))--an isotope of hydrogen.

The cause of the relatively high transition temperature of H(3)S is its hydrogen atoms, which resonate with an especially high frequency within the crystal lattice. Because deuterium atoms are heavier than hydrogen, they resonate more slowly, so lower transition temperatures were expected for D(3)S. The team at the Max-Planck Institute for Chemistry (Mainz, Germany), the University of Chicago (USA), and the Soreq Nuclear Research Center (Yavne, Israel) used a variety of analytical methods to refine the phase diagrams for H(3)S and D(3)S in relation to pressure and temperature, and to shed additional light on their superconducting properties.

At 111 to 132 GPa and 400 to 700 °C, the syntheses produced nonmetallic, electrically isolating structures (Cccm phases) that do not become a metal when cooled or pressurized further. They contain H(2) (or D(2)) units within the crystal structure, which suppress superconductivity. The desired superconducting structures, cubic Im-3m phases, were obtained by syntheses above 150 GPa at 1200 to 1700 °C. They are metallic and shiny with low electrical resistance. At 148 to 170 GPa, samples of Im-3m-H(3)S had transition temperatures around -77 °C. The D(3)S analogues had a transition temperature of about -107 °C at 157 GPa, which is significantly higher than expected. Decrease of pressure reversibly leads to an abrupt reduction of the transition temperature and loss of metallic properties. This is caused by rhombohedral distortions in the crystal structure (R3m phase). Heating under pressure irreversibly transforms the R3m phase into the Cccm phase. R3m is clearly a metastable intermediate phase that only occurs during decomposition.

In the future, the researchers hope to find other hydrogen-rich compounds that can be converted to metals without high pressures and become superconducting at room temperature.

Facts, background information, dossiers
  • hydrogen sulfide
More about MPI für Chemie
  • News

    Pinpointing Pollutants from Space

    Nitrogen oxides (NO and NO2) are major contributors to air pollution. In order to accurately predict air quality and develop strategies to reduce pollution, precise emission data are needed. Daily satellite measurements can help to derive such data. The measuring instrument observes a speci ... more

    Prestigious prize for superconductivity researcher Mikhail Eremets

    The American Physical Society (APS) awards Mikhail Eremets the 2020 James C. McGroddy Prize for New Materials. As recently announced, the researcher from the Max Planck Institute for Chemistry receives the honor for his "For pioneering studies of hydrides, a new family of high Tc materials, ... more

    A chemical criterion for rating movies

    A measurable criterion now exists for determining the age rating of films. A group of scientists at the Max Planck Institute for Chemistry in Mainz has found that the concentration of isoprene in cinema air correlates with the cinema industry‘s voluntary classification of films. Evidently, ... more

More about University of Chicago
More about Angewandte Chemie
  • News

    Cascades with carbon dioxide

    Carbon dioxide (CO2) is not just an undesirable greenhouse gas, it is also an interesting source of raw materials that are valuable and can be recycled sustainably. In the journal Angewandte Chemie, Spanish researchers have now introduced a novel catalytic process for converting CO2 into va ... more

    Structural colors from cellulose-based polymers

    A surface displays structural colors when light is reflected by tiny, regular structural elements in a transparent material. Researchers have now developed a method to make structural colors from cellulose-based polymers by using coated droplets that exist in a surrounding fluid--so-called ... more

    Trapping of Acetylene

    Ethylene, a key feedstock in the chemical industry, often includes traces of acetylene contaminants, which need to be removed. In the journal Angewandte Chemie, researchers describe a robust and regenerable porous metal–organic framework that captures acetylene with extraordinary efficiency ... more