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The researchers believe that it is mainly hydrogen
atoms that are responsible for hydrogen sulfide
losing its electrical resistance under high pressure
at relatively high temperatures: Hydrogen
atoms oscillate in the lattice with the highest
frequency of all elements, because hydrogen
is the lightest. As the oscillations of the lattice
determine the conventional superconductivity,
and do this more effectively the faster the atoms
oscillate, materials with high hydrogen content
exhibit a relatively high transition temperature.
In addition, strong bonds between the atoms
increase the temperature at which a material
becomes superconductive. These conditions are
met in H3S, and it is precisely this compound
that develops from H2S at high pressure.
Eremets and his team are now looking for materials with even higher
transition temperatures. Increasing the pressure acting on the hydrogen
sulfide above 1.5 megabar is not helpful in this case. This has not only
been calculated by theoretical physicists, but now also confirmed in
experiments performed by the team in Mainz. At even higher temperatures
the electron structure changes in such a way that the transition
temperature slowly begins to drop again.
¡°An obvious candidate for a high transition temperature is pure hydrogen,¡±
says Eremets. ¡°It is expected that it would become superconductive at
room temperature under high pressure.¡± His team has already begun
experimenting with pure hydrogen, but the experiments are very difficult
as pressures of three to four megabar are required.
¡°Our research into hydrogen sulfide has however shown that many
hydrogen-rich materials can have a high transition temperature,¡±
says Eremets. It may even be possible to realize a high-temperature
superconductor worth the name in terms of common temperature
perception without high pressure. The researchers in Mainz currently need
the high pressure to convert materials that act electrically insulating like
hydrogen sulfide into metals.
¡°There may be polymers or other hydrogen-rich compounds that can be
converted to metals in some other way and become superconductive at
room temperature,¡± says the physicist, ¡°If such materials can be found, we
would finally have superconductors that can be used for a wide range of
technical applications.¡±
Low temperature superconductivity can currently be used to levitate
objects therefore many people have longed for room-temperature versions
of today¡¯s devices. (Article continued on page 3 >>>)
Researchers Discover ¡°Holy Grail Of Superconductors¡±
Superconductivity record a historic step towards a room-temperature superconductor
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August 18, 2015: Hydrogen sulfide, the
compound responsible for the smell of rotten
eggs, has been reported to conduct electricity
with zero resistance at a record high temperature
of 203 kelvin (¨C70 ¡ãC), according to several
sources*.
Up until now, no material has been able to
conduct current with no resistance at such high
temperatures. However, recently, researchers at
the Max Planck Institute for Chemistry in Mainz,
Germany and the Johannes Gutenberg University
Mainz have observed that hydrogen sulfide
becomes superconductive at minus 70 degree
Celsius, when the substance is placed under a
pressure of 1.5 million bar. This corresponds to
half of the pressure of the earth¡¯s core.
2015 SEPTEMBER #6-8
With their high pressure experiments the researchers in Mainz have thus
not only set a new record for superconductivity, but their findings have also
highlighted a potential new way to transport current at room temperature
with no loss.
For many solid-state physicists, superconductors that are suitable for use
at room temperature are still a dream. Up until now, the only materials
known to conduct current with no electrical resistance and thus no loss
did so only at very low temperatures. Accordingly, special copper ceramics
(cuprates) took the leading positions in terms of transition temperature,
the temperature at which the material loses its resistance. The record for
a ceramic of this type is roughly minus 140 degrees Celsius at normal air
pressure and minus 109 degrees Celsius at high pressure. In the ceramics,
a special, unconventional form of superconductivity occurs. For conventional
superconductivity, temperatures of at least minus 234 degrees Celsius have
so far been necessary.
¡°With our experiments we have set a new record for the temperature at
which a material becomes superconductive,¡± says Mikhael Eremets, head of
the working group at the Max Planck Institute for Chemistry.
His team has also been the first to prove in an experiment that there
are conventional superconductors with a high transition temperature.
Theoretical calculations had already predicted this for certain substances
including H2S.
¡°There is a lot of potential in looking for other materials in which
conventional superconductivity occurs at high temperatures,¡± says the
physicist. ¡°There is theoretically no limit for the transition temperature of
conventional superconductors, and our experiments give reason to hope
that superconductivity can even occur at room temperature.¡±
Superconductor exhibiting magnetic levitation. Image:
Department of Theoretical Physics at Ural University