{"id":19104,"date":"2018-04-04T18:27:13","date_gmt":"2018-04-04T18:27:13","guid":{"rendered":"https:\/\/cnpem.staging.wpengine.com\/?p=19104"},"modified":"2022-01-21T15:34:22","modified_gmt":"2022-01-21T18:34:22","slug":"19104","status":"publish","type":"post","link":"https:\/\/cnpem.br\/en\/19104\/","title":{"rendered":"Electronic structure of uranium compounds is revealed"},"content":{"rendered":"

Ag\u00eancia FAPESP<\/a>, 28\/mar\u00e7o 2018<\/p>\n

By Jos\u00e9 Tadeu Arantes\u00a0 |\u00a0 Ag\u00eancia FAPESP<\/b>\u00a0\u2013 The actinides are a group of 15 radioactive elements that are part of the seventh row of the periodic table. This means their atoms have electrons in all seven possible energy levels. In ascending order of atomic numbers, they start with actinium (89 protons and 89 electrons) and end with lawrentium (103 protons and 103 electrons). Uranium (92) and thorium (90) are the most abundant actinides in the Earth\u2019s crust.<\/p>\n

Generally speaking, all macroscopic properties of materials \u2013 and hence their technological applications \u2013 depend on electron distribution in the outermost layers of their atoms. This is what determines whether a material is malleable or brittle, how well it conducts electricity, and whether it responds strongly or weakly to a magnetic field.<\/p>\n

The outermost orbitals can also combine to form hybrid orbitals with different shapes and energy levels. Orbital hybridization modifies the properties of atoms, how they bond to other atoms, and even the structure of the molecules formed.<\/p>\n

An experimental and theoretical study conducted at the National Synchrotron Light Laboratory (LNLS<\/a><\/b>) used X-rays to investigate the configuration of the outermost orbitals and their hybridization in uranium compounds, providing new knowledge about actinides. The properties of these materials have remained relatively unknown compared with those of lighter elements owing to the difficulty of handling them safely. This has changed thanks to the new study.<\/p>\n

An article on the study by\u00a0Narcizo Marques de Souza Neto<\/a><\/b>, first author Ricardo dos Reis and collaborators in Brazil and abroad has been\u00a0published<\/a>\u00a0<\/b>in the journal\u00a0Nature Communications<\/i>. Souza Neto designed the study and acted as principal investigator.<\/p>\n

\u201cBecause actinides are heavy elements with many electrons, they display a unique energy distribution in their last orbitals, 5f and 6d. Our main contribution was to establish experimental techniques capable of probing these outer levels. We succeeded in selectively observing the properties of layers 5f and 6d, as well as their hybridization. Previously, this hadn\u2019t been possible. Most of these materials\u2019 macroscopic properties are due to interactions between levels 5f and 6d,\u201d Souza Neto told Ag\u00eancia FAPESP.<\/p>\n

The LNLS group used a technique called X-ray magnetic circular dichroism (XMCD), with relatively high-energy X-rays in the range of 17 keV, to investigate orbitals 5f and 6d and their hybridization in uranium compounds.<\/p>\n

The XMCD technique is based on the differences between two X-ray absorption spectra in a magnetic field, one with left-polarized light and the other with right-polarized light. An analysis of these differences yields a great deal of information about the properties of the atom concerned.<\/p>\n

\u201cThis experimental technique was previously used to study other materials but had never been applied to actinides because of various operational difficulties,\u201d Souza Neto said.<\/p>\n

The study was supported by FAPESP through its\u00a0Young Investigator Grant Program<\/a><\/b>\u00a0and\u00a0Multiuser Equipment Program<\/a><\/b>, as well as a\u00a0PhD scholarship<\/a><\/b>\u00a0and a\u00a0Scientific Initiation scholarship<\/a><\/b>.<\/p>\n

Superconductors at room temperature<\/b><\/p>\n

The LNLS group worked with two silicate compounds: uranium-manganese and uranium-copper. The previously existing idea was that the compound\u2019s magnetism was entirely due to the manganese in the case of uranium-manganese and to the uranium in the case of uranium-copper.<\/p>\n

The researchers found that at room temperature, uranium-manganese also displays a degree of magnetism in the uranium, induced by the manganese, and that at low temperatures, in addition to induced magnetism, the uranium lattice is ordered independently and therefore displays even stronger magnetism.<\/p>\n

In the case of uranium-copper, the group discovered that the copper also displays magnetism induced by the uranium. All this is new knowledge produced by the study.<\/p>\n

\u201cIn addition to the behavior of uranium as a totality, we also observed what happens in its layers and sublayers, in this case 5f, 6d and the hybrid, at low and high temperatures. And we explained why it happens,\u201d Souza Neto said.<\/p>\n

\u201cThe Young Investigator grant I received from FAPESP was for the development of X-ray techniques under extreme conditions. This involved both low temperatures and high pressures with very low magnetic signals. The study we performed, which resulted in the article in\u00a0Nature Communications<\/i>, was one of the outcomes of the project. We developed the technique and succeeded in deploying several strategies to measure low signals efficiently. As a result, we were able to measure signals 50 times lower than would be measured at the other absorption edge, in this case the uranium. Thanks to the study, we now enjoy very good conditions in which to perform measurements not only in actinides but also in several other kinds of material.\u201d<\/p>\n

There are uranium compounds that are some of the few examples of unconventional superconducting materials with two antagonistic properties: ferromagnetism and superconductivity. Until now, superconductivity, the property belonging to certain materials whereby they conduct electricity without resistance or losses, has been achieved only by cooling these materials to extremely low temperatures.<\/p>\n

A deeper understanding of these unconventional uranium compounds could be a key step toward obtaining a material that is a superconductor at room temperature. This would have an extraordinary technological and social impact.<\/p>\n

\u201cAlthough our research was conducted strictly as basic science, technological developments as interesting as this are by no means beyond its horizons,\u201d Souza Neto said.<\/p>\n

The article \u201cUnraveling 5f-6d hybridization in uranium compounds via spin-resolved L-edge spectroscopy\u201d by R. D. dos Reis, L. S. I. Veiga, C. A. Escanhoela Jr., J. C. Lang, Y. Joly, F. G. Gandra, D. Haskel and N. M. Souza-Neto can be read at:\u00a0nature.com\/articles\/s41467-017-01524-1<\/a><\/b>.<\/p>\n","protected":false},"excerpt":{"rendered":"

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