How is a metal formed?

June 05, 2020

What does it mean to be a metal and how is a metal formed? These seem like textbook questions with a simple answer: Metal is characterized by free electrons which give rise to its high electric conductivity. But how exactly is a metallic conduction band formed from originally localized electrons and what is the corresponding microscopic picture for the material involved?

In collaboration involving scientists from the Czech Republic, USA, and Germany, the Science, one of the most prestigious scientific journals in the world, which also selected the study for cover image.

Alkali metals dissolved in liquid ammonia represent archetypal systems to explore the transition from blue electrolytes at low concentrations to bronze or gold colored metallic solutions (with conductivity comparable to a copper wire) with higher concentrations of excess electrons. At the same time, PES represents an ideal tool for establishing the electronic structure pertinent to this transition. As an ultra-high vacuum technique, PES was long thought to be incompatible with volatile liquids until the technique of liquid microjets was developed for water and aqueous solutions. However, it was only in 2019 that the group of Pavel Jungwirth in collaboration with colleagues at the University of Southern California and at the BESSY II synchrotron in Berlin performed first successful PES measurements on a refrigerated polar liquid - pure liquid ammonia.

"This is what happens when you give a theory group a bit of lab space to play," says Pavel Jungwirth of the decision of the Institute's director to grant him a small laboratory.

This achievement opened the door to PES studies of alkali metal - liquid ammonia systems (as reported in the present paper in Science), which map the electrolyte-to-metal transition for lithium, sodium, and potassium dissolved in liquid ammonia by means of PES using soft X-ray synchrotron radiation. In this way, researchers captured for the first time the photoelectron signal of excess electrons in liquid ammonia as a peak at around 2 eV binding energy. This peak then broadens asymmetrically toward higher binding energies upon increasing the alkali metal concentration, gradually forming a conduction band with a sharp Fermi edge accompanied by plasmon peaks, both of which being fingerprints of the nascent metallic behavior.

Together with state-of-the-art electronic structure calculations, these measurements provide a detailed molecular picture of the transition from a non-metal to a metal, allowing us to better understand the onset of metallic behavior characterized by properties such as the very large electric conductivity.

"Hopefully the present work on metallic ammonia will open the path to realizing our most 'explosive' idea: The preparation of metallic water by very carefully mixing it with alkali metals," concludes Pavel Jungwirth.
Original paper: Buttersack T., Mason P.E., McMullen R.S., Schewe C., Martínek T., B?ezina K., Crhan M., Gomez A., Hein D., Wartner G., Seidel R., Ali H., Thurmer S., Maršálek O., Winter B., Bradforth S.E., Jungwirth P.: Photoelectron spectra of alkali metal-ammonia microjets: From blue electrolyte to bronze metal. Science, June 5, 2020, DOI: 10.1126/science.aaz7607.

Professor Pavel Jungwirth, DSc. (b. 1966, Prague) is a Czech physical chemist, educator, and popularizer of science. He studied physics in Prague at Charles University, Faculty of Mathematics and Physics, where he specialized in chemical physics. He received his Candidate of Sciences degree from the J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences for his work in computational chemistry under the guidance of Professor R. Zahradník. He has spent several years at the University of California, Irvine, the University of Southern California in Los Angeles, and the Hebrew University of Jerusalem.

Currently, Pavel Jungwirth heads a research team at the Institute of Organic Chemistry and Biochemistry of the

Pavel Jungwirth has published more than 300 original papers in international journals, including Science, Nature Chemistry, and PNAS, with over 14,000 citations. He is a senior editor of the Journal of Physical Chemistry, which is published by the American Chemical Society. He is also the president of the Learned Society of the Czech Republic and has received numerous awards, among them the Spiers Memorial Prize of the British Royal Society of Chemistry and the Jaroslav Heyrovský Honorary Medal for Merit in the Chemical Sciences from the Czech Academy of Sciences. Pavel Jungwirth's popular-science contributions regularly appear on the pages of the weekly Respekt, and he is a frequent Czech Radio and television guest.

The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences /
IOCB Prague is a leading internationally recognized scientific institution whose primary mission is the pursuit of basic research in chemical biology and medicinal chemistry, organic and materials chemistry, chemistry of natural substances, biochemistry and molecular biology, physical chemistry, theoretical chemistry, and analytical chemistry. An integral part of the IOCB Prague's mission is the implementation of the results of basic research in practice. Emphasis on interdisciplinary research gives rise to a wide range of applications in medicine, pharmacy, and other fields. Video:
Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences (IOCB Prague)

Related Metal Articles from Brightsurf:

Blue phosphorus: How a semiconductor becomes a metal
Blue phosphorus, an atomically thin synthetic semiconductor, becomes metallic as soon as it is converted into a double layer.

Vaporized metal in the air of an exoplanet
An international team of researchers led by the National Centre of Competence in Research PlanetS of the University of Bern and the University of Geneva studied the atmosphere of the ultra-hot exoplanet WASP-121b.

Turning diamond into metal
Researchers have discovered a way to tweak tiny needles of diamond in a controlled way to transform their electronic properties, dialing them from insulating, through semiconducting, all the way to highly conductive, or metallic.

The best of both worlds: A new take on metal-plastic hybrid 3D printing
Current 3D printers employ either plastic or metal only, and the conventional method to coat 3D plastic structures with metal is not environment-friendly and yields poor results.

Metal-ion breakthrough leads to new biomaterials
Metals such as iron and calcium play a crucial role inside the human body, so it's no surprise that bioengineers would like to integrate them into the soft, stretchy materials used to repair skin, blood vessels, lungs and other tissue.

How is a metal formed?
Metal is characterized by free electrons which give rise to its high electric conductivity.

Tuning the surface gives variations to metal foils
IBS researchers reported how to give variations to single crystalline metal foils.

Metal collector made of bacteria
Bacteria, fungi and plants sometimes produce metal-binding substances that can be harnessed, for example for the extraction of raw materials, for their separation, for cleaning soils or for medical purposes.

Noble metal aerogels enabled by freezing
TU Dresden chemists developed a freeze-thaw method, capable of synthesising various noble metal aerogels (NMAs) with clean surfaces and multiscale structure.

Wetting property of Li metal with graphite
Compositing two classic anode materials, graphite and Li metal, has shown promising performance to go beyond the traditional Li-ion batteries.

Read More: Metal News and Metal Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to