̽��ֱ�� of Cambridge - Chris Pickard

New phases of water detected

sc604 — Wed, 14 Sep 2022 15:27:56 +0000

Scientists at the ̽��ֱ�� of Cambridge have discovered that water in a one-molecule layer acts like neither a liquid nor a solid, and that it becomes highly conductive at high pressures.

Much is known about how ‘bulk water’ behaves: it expands when it freezes, and it has a high boiling point. But when water is compressed to the nanoscale, its properties change dramatically.

By developing a new way to predict this unusual behaviour with unprecedented accuracy, the researchers have detected several new phases of water at the molecular level.

Water trapped between membranes or in tiny nanoscale cavities is common – it can be found in everything from membranes in our bodies to geological formations. But this nanoconfined water behaves very differently from the water we drink.

Until now, the challenges of experimentally characterising the phases of water on the nanoscale have prevented a full understanding of its behaviour. But in a paper published in the journal Nature, the Cambridge-led team describe how they have used advances in computational approaches to predict the phase diagram of a one-molecule thick layer of water with unprecedented accuracy.

They used a combination of computational approaches to enable the first-principles level investigation of a single layer of water.

̽��ֱ��researchers found that water which is confined into a one-molecule thick layer goes through several phases, including a ‘hexatic’ phase and a ‘superionic’ phase. In the hexatic phase, the water acts as neither a solid nor a liquid, but something in between. In the superionic phase, which occurs at higher pressures, the water becomes highly conductive, propelling protons quickly through ice in a way resembling the flow of electrons in a conductor.

Understanding the behaviour of water at the nanoscale is critical to many new technologies. ̽��ֱ��success of medical treatments can be reliant on how water trapped in small cavities in our bodies will react. ̽��ֱ��development of highly conductive electrolytes for batteries, water desalination, and the frictionless transport of fluids are all reliant on predicting how confined water will behave.

“For all of these areas, understanding the behaviour of water is the foundational question,” said Dr Venkat Kapil from Cambridge’s Yusuf Hamied Department of Chemistry, the paper’s first author. “Our approach allows the study of a single layer of water in a graphene-like channel with unprecedented predictive accuracy.”

̽��ֱ��researchers found that the one-molecule thick layer of water within the nanochannel showed rich and diverse phase behaviour. Their approach predicts several phases which include the hexatic phase--an intermediate between a solid and a liquid--and also a superionic phase, in which the water has a high electrical conductivity.

“ ̽��ֱ��hexatic phase is neither a solid nor a liquid, but an intermediate, which agrees with previous theories about two-dimensional materials,” said Kapil. “Our approach also suggests that this phase can be seen experimentally by confining water in a graphene channel.

“ ̽��ֱ��existence of the superionic phase at easily accessible conditions is peculiar, as this phase is generally found in extreme conditions like the core of Uranus and Neptune. One way to visualise this phase is that the oxygen atoms form a solid lattice, and protons flow like a liquid through the lattice, like kids running through a maze.”

̽��ֱ��researchers say this superionic phase could be important for future electrolyte and battery materials as it shows an electrical conductivity 100 to 1,000 times higher than current battery materials.

̽��ֱ��results will not only help with understanding how water works at the nanoscale, but also suggest that ‘nanoconfinement’ could be a new route into finding superionic behaviour of other materials.

Dr Venkat Kapil is a Junior Research Fellow at Churchill College, Cambridge. ̽��ֱ��research team included Dr Christoph Schran and Professor Angelos Michaelides from the Yusuf Hamied Department of Chemistry ICE group, working with Professor Chris Pickard at the Department of Materials Science & Metallurgy, Dr Andrea Zen from the ̽��ֱ�� of Naples Federico II and Dr Ji Chen from Peking ̽��ֱ��.

Reference:
Angelos Michaelides et al. ‘ ̽��ֱ��first-principles phase diagram of monolayer nanoconfined water.’ Nature (2022). DOI: 10.1038/s41586-022-05036-x

Water can be liquid, gas or ice, right? Think again.

One way to visualise this phase is that the oxygen atoms form a solid lattice, and protons flow like a liquid through the lattice, like kids running through a maze

Venkat Kapil

Daniel Sonoca via Unsplash

Water

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Scientists find upper limit for the speed of sound

Anonymous — Mon, 12 Oct 2020 09:17:26 +0000

̽��ֱ��result - about 36km per second - is around twice as fast as the speed of sound in diamond, the hardest known material in the world.

Waves, such as sound or light waves, are disturbances that move energy from one place to another. Sound waves can travel through different mediums, such as air or water, and move at different speeds depending on what they’re travelling through. For example, they move through solids much faster than they would through liquids or gases, which is why you’re able to hear an approaching train much faster if you listen to the sound propagating in the rail track rather than through the air.

Einstein’s theory of special relativity sets the absolute speed limit at which a wave can travel which is the speed of light and is equal to about 300,000km per second. However, until now it was not known whether sound waves also have an upper speed limit when travelling through solids or liquids.

̽��ֱ��study, published in the journal Science Advances, shows that predicting the upper limit of the speed of sound is dependent on two dimensionless fundamental constants: the fine structure constant and the proton-to-electron mass ratio.

These two numbers are already known to play an important role in understanding our Universe. Their finely-tuned values govern nuclear reactions such as proton decay and nuclear synthesis in stars and the balance between the two numbers provides a narrow ‘habitable zone’ where stars and planets can form and life-supporting molecular structures can emerge. However, the new findings suggest that these two fundamental constants can also influence other scientific fields, such as materials science and condensed matter physics, by setting limits to specific material properties such as the speed of sound.

̽��ֱ��scientists tested their theoretical prediction on a wide range of materials and addressed one specific prediction of their theory that the speed of sound should decrease with the mass of the atom. This prediction implies that the sound is the fastest in solid atomic hydrogen. However, hydrogen is an atomic solid at very high pressure above 1 million atmospheres only, pressure comparable to those in the core of gas giants like Jupiter. At those pressures, hydrogen becomes a fascinating metallic solid conducting electricity just like copper and is predicted to be a room-temperature superconductor. Therefore, researchers performed state-of-the-art quantum mechanical calculations to test this prediction and found that the speed of sound in solid atomic hydrogen is close to the theoretical fundamental limit.

Professor Chris Pickard, from Cambridge's Department of Materials Science and Metallurgy, said: “Soundwaves in solids are already hugely important across many scientific fields. For example, seismologists use sound waves initiated by earthquakes deep in the Earth's interior to understand the nature of seismic events and the properties of Earth's composition. They’re also of interest to materials scientists because sound waves are related to important elastic properties including the ability to resist stress.”

Professor Kostya Trachenko, Professor of Physics at Queen Mary, said: “We believe the findings of this study could have further scientific applications by helping us to find and understand limits of different properties such as viscosity and thermal conductivity relevant for high-temperature superconductivity, quark-gluon plasma and even black hole physics.”

Reference:
K. Trachenko et al. ‘Speed of sound from fundamental physical constants.’ Science Advances (2020). DOI: 10.1126/sciadv.abc8662

Adapted from a Queen Mary ̽��ֱ�� of London press release.

A research collaboration between the ̽��ֱ�� of Cambridge, Queen Mary ̽��ֱ�� of London and the Institute for High Pressure Physics in Troitsk has discovered the fastest possible speed of sound.

PublicDomainPictures from Pixabay

Soundwave

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Quantum effects at work in the world’s smelliest superconductor

sc604 — Mon, 28 Mar 2016 15:00:00 +0000

̽��ֱ��quantum behaviour of hydrogen affects the structural properties of hydrogen-rich compounds, which are possible candidates for the elusive room temperature superconductor, according to new research co-authored at the ̽��ֱ�� of Cambridge.

New theoretical results, published online in the journal Nature, suggest that the quantum nature of hydrogen – meaning that it can behave like a particle or a wave – strongly affects the recently discovered hydrogen sulphur superconductor, a compound that when subjected to extremely high pressure, is the highest-temperature superconductor yet identified. This new step towards understanding the underlying physics of high temperature superconductivity may aid in the search for a room temperature superconductor, which could be used for applications such as levitating trains, lossless electrical grids and next-generation supercomputers.

Superconductors are materials that carry electrical current with zero electrical resistance. Low-temperature, or conventional, superconductors were first identified in the early 20th century, but they need to be cooled close to absolute zero (zero degrees on the Kelvin scale, or -273 degrees Celsius) before they start to display superconductivity. For the past century, researchers have been searching for materials that behave as superconductors at higher temperatures, which would make them more suitable for practical applications. ̽��ֱ��ultimate goal is to identify a material which behaves as a superconductor at room temperature.

Last year, German researchers identified the highest temperature superconductor yet – hydrogen sulphide, the same compound that gives rotten eggs their distinctive odour. When subjected to extreme pressure – about one million times higher than the Earth’s atmospheric pressure – this stinky compound displays superconducting behaviour at temperatures as high as 203 Kelvin (-70 degrees Celsius), which is far higher than any other high temperature superconductor yet discovered.

Since this discovery, researchers have attempted to understand what it is about hydrogen sulphide that makes it capable of superconducting at such high temperatures. Now, new theoretical results suggest that the quantum behaviour of hydrogen may be the reason, as it changes the structure of the chemical bonds between atoms. ̽��ֱ��results were obtained by an international collaboration of researchers led by the ̽��ֱ�� of the Basque Country and the Donostia International Physics Center, and including researchers from the ̽��ֱ�� of Cambridge.

̽��ֱ��behaviour of objects in our daily life is governed by classical, or Newtonian, physics. If an object is moving, we can measure both its position and momentum, to determine where an object is going and how long it will take to get there. ̽��ֱ��two properties are inherently linked.

However, in the strange world of quantum physics, things are different. According to a rule known as Heisenberg’s uncertainty principle, in any situation in which a particle has two linked properties, only one can be measured and the other must be uncertain.

Hydrogen, being the lightest element of the periodic table, is the atom most strongly subjected to quantum behaviour. Its quantum nature affects structural and physical properties of many hydrogen compounds. An example is high-pressure ice, where quantum fluctuations of the proton lead to a change in the way that the molecules are held together, so that the chemical bonds between atoms become symmetrical.

̽��ֱ��researchers behind the current study believe that a similar quantum hydrogen-bond symmetrisation occurs in the hydrogen sulphide superconductor.

Theoretical models that treat hydrogen atoms as classical particles predict that at extremely high pressures – even higher than those used by the German researchers for their record-breaking superconductor – the atoms sit exactly halfway between two sulphur atoms, making a fully symmetrical structure. However, at lower pressures, hydrogen atoms move to an off-centre position, forming one shorter and one longer bond.

̽��ֱ��researchers have found that when considering the hydrogen atoms as quantum particles behaving like waves, they form symmetrical bonds at much lower pressures – around the same as those used for the German-led experiment, meaning that quantum physics, and symmetrical hydrogen bonds, were behind the record-breaking superconductivity.

“That we are able to make quantitative predictions with such a good agreement with the experiments is exciting and means that computation can be confidently used to accelerate the discovery of high temperature superconductors,” said study co-author Professor Chris Pickard of Cambridge’s Department of Materials Science & Metallurgy.

According to the researcher’s calculations, the quantum symmetrisation of the hydrogen bond has a tremendous impact on the vibrational and superconducting properties of hydrogen sulphide. “In order to theoretically reproduce the observed pressure dependence of the superconducting critical temperature the quantum symmetrisation needs to be taken into account,” said the study’s first author, Ion Errea, from the ̽��ֱ�� of the Basque Country and Donostia International Physics Center.

̽��ֱ��discovery of such a high temperature superconductor suggests that room temperature superconductivity might be possible in other hydrogen-rich compounds. ̽��ֱ��current theoretical study shows that in all these compounds, the quantum motion of hydrogen can strongly affect the structural properties, even modifying the chemical bonding, and the electron-phonon interaction that drives the superconducting transition.

“Theory and computation have played an important role in the hunt for superconducting hydrides under extreme compression,” said Pickard. “ ̽��ֱ��challenges for the future are twofold - increasing the temperature towards room temperature, but, more importantly, dramatically reducing the pressures required.”

Reference:
Ion Errea et. al. ‘Quantum hydrogen-bond symmetrization in the superconducting hydrogen sulfide system.’ Nature (2016).DOI: 10.1038/nature17175.

Researchers have found that quantum effects are the reason that hydrogen sulphide – which has the distinct smell of rotten eggs –behaves as a superconductor at record-breaking temperatures, which may aid in the search for room temperature superconductors.

That we are able to make quantitative predictions with such a good agreement with the experiments is exciting and means that computation can be confidently used to accelerate the discovery of high temperature superconductors.

Chris Pickard

UPV/EHU

Structure with symmetric hydrogen bonds induced by the quantum behavior of the protons, represented by the fluctuating blue spheroids

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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