Web Date: June 10, 2015
Searching The Periodic Table For Novel Solids
As-yet-undiscovered materials that could be the key to better electronics or solar cells may give the first glimpse of themselves to a computer. A team of theoreticians has now explored the periodic table and identified silver, copper, and gold oxides with never-before-seen structures (Chem. Mater. 2015, DOI: 10.1021/acs.chemmater.5b00716). Their search accelerates the hunt for new materials by establishing that it can be done on a much larger computational scale than pursuits of the past.
The work of finding new, stable combinations of elements is like combing a beach for sand dollars. A beachcomber might do a quick search at the tide line where sand dollars tend to lie. But to find all of them, a seeker must methodically walk the length and width of the beach.
In the past, theoretical chemists have mostly searched for new materials by starting with known crystal structures from nature, switching up the elements, and then looking for stable variations. This quick method works, but it doesn’t find structures different than ones that are already known, says Miguel A. L. Marques of Martin Luther University of Halle-Wittenberg, in Germany.
So Marques set out to show that researchers now have the computational power, codes, and algorithms to perform more thorough searches of hundreds of element combinations. Marques found ways to streamline a technique called global structural prediction and use it for new-materials discovery—the equivalent of walking the entire beach to find sand dollars.
Marques and his coworkers focused on three-element oxides of copper, gold, and silver—183 different combinations. Such oxides tend to be transparent and conducting, and therefore could be useful in touch screens and solar cells. The team wanted to screen for stable configurations and predict whether any might be promising enough for experimental chemists to synthesize and test.
To search for all possible structures of each oxide, the researchers programmed the Curie supercomputer at the Very Large Computing Center (TGCC), in France, to start with a random structure and rearrange it until it found a stable, low-energy configuration. After creating three or four structures this way, the researchers applied a technique that traverses the energy landscape from one relatively stable structure to the next, comparing structures along the way, and repeats this journey until it identifies the ground-state structure with the lowest energy.
After evaluating 21,000 low-energy structures, the computer unearthed 81 stable compositions. Of those, only 36 have been reported. Some of the structures, such as silver bismuth oxide (AgBiO2), have never been observed or predicted before.
Two structures in particular, silver scandium oxide (AgScO2) and silver yttrium oxide (AuYO2), have some predicted properties that make them potential transparent conductors, says Renaud Leturcq of the Luxembourg Institute of Science & Technology. But this is “a preliminary study that requires more precise calculation” to fully evaluate their properties, he adds.
The gold and silver in these candidates means making and using these materials would be expensive, adds M. Geoffroy Hautier of Catholic University of Louvain, in Belgium. Hautier is more excited by how the study applies global structural prediction on a much larger scale than before. “I am sure that people will start doing it more and more,” he says.
Since the study, Marques and his collaborators have compared not just hundreds of compositions at a time, but thousands. “The number we can try,” he says, “is just limited by the size of the supercomputer.”
- Chemical & Engineering News
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