Drexel University researchers are turning some of the basic tenets of chemistry and physics upside down to cut a trail toward the discovery of a new set of materials. They’re called “polar metals” and, according to many of the scientific principles that govern the behavior of atoms, they probably shouldn’t exist.
James Rondinelli, PhD, a professor in the College of Engineering, and Danilo Puggioni, PhD, a postdoctoral researcher in the College, have shed light on this rare breed of electrically conductive polar metal—whose atomic makeup actually has more in common with a drop of water than a flake of rust—using an advanced computing method called density functional theory.
This automated system of virtual chemical match-making sifts through volumes of structural chemistry data to churn out combinations of elements that could exist as stable compounds. Rondinelli and Puggioni, both members of Drexel’s Material’s Theory and Design Group in the College's Materials Science Engineering department, worked through a step-by-step process to isolate shared features of known polar metals, thus creating a way to classify them.
“We sought first to classify all known compounds and look for commonalities and ways to systematically describe them,” Rondinelli said. “By creating the classification scheme we identified the key features. That knowledge was formulated into a working principle that allowed us to predict a new compound using quantum mechanical calculations.”
These metals are considered rare because of their unusual atomic and chemical structure, specifically, an imbalanced distribution of electrons in a material with metal cations and oxygen. Most metallic materials have an even or symmetric distribution of electrons, in other words it does not have positively and negatively charged poles. But these asymmetric polar metals, appear to be an exception to the rule.
“They challenge our notions of what it means for a material to be a metal or to be polar,” Rondinelli said. “By polar, I mean just like the water molecule, which has an asymmetric distribution of charge. It’s nearly the same case here, where the material we predict is polar, but it is simultaneously metallic owing to mobile electrons, rather than bound electrons.”
Scientists have hypothesized the existence of polar metals, dubbed “metallic ferroeletrics” by Nobel Laureate Phil Anderson, since the 1960s -but with little theoretical understanding of how to discover them. Since then, researchers have essentially stumbled upon about 30 metals with asymmetric charge distributions.
More than half a century later, Rondinelli and Puggioni were able to examine the crystal structure of these known polar metals, and show that the geometric arrangement of atoms is key to understanding their asymmetric charge distribution. This information, in turn, will make it possible for materials scientists to discover more compounds.
Putting their theory to the test, the duo designed a polar metal of their own. The material, chemically termed strontium-calcium ruthenate, (Sr,Ca)RuO6, is currently in the theoretical stage, but Rondinelli and Puggioni are working with experimental groups around the country to produce the compound in a laboratory.
While it’s too early to predict what applications these materials are ideally suited for, other materials in this class of polar metals are superconducting—they are able to conduct electricity with zero resistance—so they could find use in a variety of advanced electronic and thermal devices. The pair’s research was funded by the Army Research Office’s Young Investigator Program and was recently published in Nature Communications.
“The way these materials behave and the reasons for their stability are rather unconventional, yet our classification scheme provides a general design strategy that could guide the discovery and realization of many more polar metals,” said Rondinelli. “I don’t believe these materials are as rare as is currently thought despite their counterintuitive nature; researchers may have simply been looking in the wrong places.”
Puggioni D. & Rondinelli J.M. (2014). Designing a robustly metallic noncenstrosymmetric ruthenate oxide with large thermopower anisotropy, Nature Communications, 5 DOI: 10.1038/ncomms4432
News Officer, University Communications
Britt Faulstick | EurekAlert!
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Trade Fair News
16.01.2017 | Automotive Engineering
16.01.2017 | Life Sciences