On the road to conductors of the future

Date:
September 14, 2020
Source:
Wiley
Summary:
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. Scientists 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 DEGC, respectively.



FULL STORY ========================================================================== 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 DEGC, respectively.


==========================================================================
This is even true in comparison with the current front-runners, copper- containing ceramics with transition temperatures that start at about
-135 DEGC.

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 DEGC, 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 DEGC. 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 DEGC. The D(3)S
analogues had a transition temperature of about -107 DEGC 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.


========================================================================== Story Source: Materials provided by Wiley. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Vasily S. Minkov, Vitali B. Prakapenka, Eran Greenberg, Mikhail I.

Eremets. A Boosted Critical Temperature of 166 K in
Superconducting D 3 S Synthesized from Elemental Sulfur and
Hydrogen. Angewandte Chemie International Edition, 2020; DOI:
10.1002/anie.202007091 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200914112152.htm

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