Chemists from Russia opened the «impossible» connection of gold

© AP Photo / Mike GrollЗолотые barsChemists from Russia opened the «impossible» connection of gold© AP Photo / Mike GrollПодпишись to daily updates RIA Science

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. Scientists from Russia and Germany uncovered the secret of the stability calaverita, strange and rare mineral of gold, and found evidence that noble metal can form a very unusual compound with tellurium. Their findings and calculations were presented in the journal PNAS.

«The mineral calaverite amazing destiny. Noticeably influenced the «gold rush» for many decades it was a headache and more of a paradox for crystallography. The deeper he studied, the more new questions arose. Our team managed to tie all the weirdness calaverita in the framework of the simple model, experimenters can now hunt predicted a new connection,» — says Artem Oganov, Professor of Skoltech and MIPT.

Gold, unlike most other metals, high chemical inertness and almost never found in nature in the form of large deposits of various compounds with other elements. Most of the inventory of gold mined by mankind until the early 20th century, was found in the form of nuggets and the net deposits of this metal.

The only exception to this rule is mineral calaverite, a compound of gold and tellurium AuTe2. He has long been interested not only miners, but also chemists and physicists, as calaverite has a very unusual structure, which cannot be explained within the classical theory of the structure of crystals. Only relatively recently have scientists solved the mystery of the device, describing it in four-dimensional space.

This description, as noted by Oganov and his colleagues created a new problem – the gold in these crystals will have a «wrong» oxidation state is +2, that will make them unstable from the point of view of chemistry. Russian scientists and their German colleagues figured out why calaverite still exists, using USPEX, Oganov created several years ago for predicting the properties of chemical elements and crystals.

To do this, scientists first had to consider how it is possible to calculate the properties of such complex compounds. They found a way out of this situation, using other natural mineral gold – Silvana, its connection with the tellurium and silver, as a kind of «template» to calculate the properties of the individual parts calaverita.

Calculated properties of sylvanite and substituting silver atoms for gold, Oganov and his team found that will calaverite is not gold, oxidized to the extent of +2, and mixtures of atoms in two different oxidation States — +1 and +3, distributed over the crystal in a special way.

«Place of monovalent and trivalent gold, even if it existed, so that they recurred equally in each direction, on a triangular lattice calaverita simply impossible. Therefore, nature is forced to compromise – to smoothly change the valence of the gold in the crystal. The environment of tellurium reacts to it, which leads to unusual distortions of the crystal lattice,» explains Sergey Streltsov Institute of metal physics, Russian Academy of Sciences in Yekaterinburg.

These calculations, as they note, revealed several interesting and unusual properties calaverita. In particular, it was found that it can be turned into a superconductor, and holding up to extreme pressure or adding atoms of platinum and some other metals. Such behavior, according to chemists, is not typical for gold compounds.

In addition, calculations by Oganov and his colleagues suggest that there may be another «impossible» compounds of gold and tellurium AuTe. As suggested by the chemist, it will also have an unusual structure and interesting properties, including superconductivity.

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