Unusual electron sharing found in cool crystal

Date:
July 31, 2020
Source:
Nagoya University
Summary:
Tungsten atoms are seen to come together in a way that is similar
to an outer space ion. The finding suggests many more types of
electron sharing between atoms could exist in nature.



FULL STORY ==========================================================================
A team of scientists led by Nagoya University in Japan has detected a
highly unusual atomic configuration in a tungsten-based material. Until
now, the atomic configuration had only been seen in trihydrogen, an ion
that exists in between star systems in space. The findings, published in
the journal Nature Communications, suggest further studies could reveal compounds with interesting electronic properties.


========================================================================== Atoms that make up humans and trees and kitchen tables generally bond
together by sharing electrons -- think of electrons as the atomic glue of
life. Nagoya University applied physicist Yoshihiko Okamoto and colleagues
have found a highly unusual version of this glue: a regular triangular
molecule was formed of three atoms bonded together by two electrons.

"This type of bond had only previously been seen in the trihydrogen ions
found in interstellar material," says Okamoto. "We were excited to see
this configuration in a cooled tungsten-based crystal." The so-called tritungsten molecules were discovered in single crystals of caesium
tungsten oxide (CsW2O6) cooled below -58DEGC. CsW2O6 conducts electricity
at room temperature but changes into an insulating material when it is
cooled below -58DEGC. It has been a challenge to study how the atomic
structure of this type of material changes in response to temperature. To overcome this, Okamoto and his colleagues in Japan synthesized very pure
single crystals of CsW2O6 and bombarded them with X-ray beams at room temperature and -58DEGC.

The tungsten molecules in the conducting crystal form three-dimensional networks of tetrahedral pyramids connected at their corners, known as
a pyrochlore structure. The bonds between the molecules form due to a symmetrical sharing of electrons between them.

However, when the compound is cooled, the electrons re-arrange and
two types of tungsten atoms emerge within the tetrahedra, each with a
different 'valence', or bonding power with other atoms. This, in turn,
distorts the lengths of tungsten bonds with oxygen atoms in the compound, leading to a more compressed shape. Importantly, the tungsten atoms
with lower valence form small and large triangles on the sides of the
tungsten tetrahedra, with the highly unusual tritungsten molecules
forming on the small triangles. The three tungsten atoms forming the
points of these triangles share only two electrons between them to keep
them bonded together.

"To our knowledge, CsW2O6 is the only example where this type of bond formation, where several atoms share only a few electrons, appears as
a phase transition," says Okamoto.

The team aims to further investigate compounds with pyrochlore structures,
with the ultimate goal of discovering materials with new and interesting properties.


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


========================================================================== Journal Reference:
1. Yoshihiko Okamoto, Haruki Amano, Naoyuki Katayama, Hiroshi Sawa,
Kenta
Niki, Rikuto Mitoka, Hisatomo Harima, Takumi Hasegawa, Norio
Ogita, Yu Tanaka, Masashi Takigawa, Yasunori Yokoyama, Kanji
Takehana, Yasutaka Imanaka, Yuto Nakamura, Hideo Kishida, Koshi
Takenaka. Regular-triangle trimer and charge order preserving the
Anderson condition in the pyrochlore structure of CsW2O6. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-16873-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200731085641.htm

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