Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers improve description of defective oxides with first principles calculation

13.03.2019

Team develops site-dependent +U correction parameters

Some perovskite oxides, for example, have shown a wide spectrum of technologically relevant functional properties such as ferroelectricity and magnetism that can be tuned via strain. Strain, however, also couples with the defect chemistry to determine the material's properties.


Understanding how defects can affect ground-state properties, promote phase transitions, or enable entirely new functionalities in some strongly correlated oxides has become a subject of major interest in the field of design and discovery of novel functional materials. SrMnO3 (SMO) is a particularly interesting example, but better characterization is needed. MARVEL researchers have now a developed a method that may lead to more accurate predictions of the energetics of defects associated with in-gap states in semiconductors or insulators.

Credit: Ulrich Aschauer

SrMnO3 (SMO) is a particularly interesting example for examining the functionality resulting from a complex interplay of strain, magnetic order, polar distortions, and oxygen vacancies that are ubiquitous defects in these materials. In particular, theory has predicted SMO thin films to turn from antiferromagnetic to ferromagnetic with increasing oxygen deficiency, which is supported by recent experimental studies.

These previous predictions were however based on density functional theory (DFT) calculations that incorporated a correction U based on the electronic and magnetic properties of stoichiometric manganites. While the inclusion of U--meant to correct self-interaction of electrons in complex oxides--is necessary in such materials, the specific choice of U based on stoichiometric material properties could lead to potential shortcomings in the description of defective SMO--manganese ions around the defect have a different coordination environment.

... more about:
»accurate »ions »magnetic phase »materials »strain

Depending on the defect charge state, an added issue is related to the description of multiple oxidation states present in defective SMO. The formation of oxygen vacancies is generally charge-compensated by a reduction of the oxidation state (OS) of manganese ions adjacent to the vacancy, which may thus not be properly described by the same U.

This is why University of Bern postdoc Chiara Ricca and colleagues decided it was critical to take into account local structural and chemical effects for each transition metal site in the oxide when aiming for an accurate description of defective SMO.

In collaboration with a team at Nicola Marzari's THEOS lab/, which recently developed a density functional perturbation theory (DFPT)-based approach to compute U parameters, they used self-consistent site-dependent U values computed from first principles to study the defect chemistry and magnetic properties of SMO bulk and strained thin films.

"This extremely close collaboration between the two groups, one focusing on methods development and the other on applications in defective oxide materials, was sparked by uniting these different research foci under the MARVEL umbrella" said the University of Bern's Ulrich Aschauer, one of the two PIs involved in the work.

The results show that this self-consistent U improves the structure of stoichiometric SrMnO3 with respect to other methods, including one using an empirical U. For defective systems, U changes as a function of the distance of the transition-metal site from the defect, its oxidation state, its coordination number, and the magnetic phase of the material.

Taking into account this dependence, in turn, affects the computed defect formation energies and the predicted strain- and/or defect-induced magnetic phase transitions, especially when occupied localized states appear in the band gap of the material upon defect creation.

"We believe this approach can lead to more accurate predictions of the energetics of defects associated with in-gap states in semiconductors or insulators both compared to standard DFT and possibly hybrid functionals at a computational cost that is significantly lower than for the latter," Ricca said. "This is thanks to a proper description of the structural and local chemical effects induced by the defects."

Ulrich Aschauer | EurekAlert!
Further information:
http://nccr-marvel.ch/highlights/2019-03defective-oxides

Further reports about: accurate ions magnetic phase materials strain

More articles from Materials Sciences:

nachricht Fraunhofer LBF and BAM develop faster procedure for flame-retardant plastics
21.10.2019 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

nachricht For EVs with higher range: Take greater advantage of the potential offered by lightweight construction materials
21.10.2019 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A cavity leads to a strong interaction between light and matter

Researchers have succeeded in creating an efficient quantum-mechanical light-matter interface using a microscopic cavity. Within this cavity, a single photon is emitted and absorbed up to 10 times by an artificial atom. This opens up new prospects for quantum technology, report physicists at the University of Basel and Ruhr-University Bochum in the journal Nature.

Quantum physics describes photons as light particles. Achieving an interaction between a single photon and a single atom is a huge challenge due to the tiny...

Im Focus: Solving the mystery of quantum light in thin layers

A very special kind of light is emitted by tungsten diselenide layers. The reason for this has been unclear. Now an explanation has been found at TU Wien (Vienna)

It is an exotic phenomenon that nobody was able to explain for years: when energy is supplied to a thin layer of the material tungsten diselenide, it begins to...

Im Focus: An ultrafast glimpse of the photochemistry of the atmosphere

Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols.

The nanocosmos is constantly in motion. All natural processes are ultimately determined by the interplay between radiation and matter. Light strikes particles...

Im Focus: Shaping nanoparticles for improved quantum information technology

Particles that are mere nanometers in size are at the forefront of scientific research today. They come in many different shapes: rods, spheres, cubes, vesicles, S-shaped worms and even donut-like rings. What makes them worthy of scientific study is that, being so tiny, they exhibit quantum mechanical properties not possible with larger objects.

Researchers at the Center for Nanoscale Materials (CNM), a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE's Argonne National...

Im Focus: Novel Material for Shipbuilding

A new research project at the TH Mittelhessen focusses on the development of a novel light weight design concept for leisure boats and yachts. Professor Stephan Marzi from the THM Institute of Mechanics and Materials collaborates with Krake Catamarane, which is a shipyard located in Apolda, Thuringia.

The project is set up in an international cooperation with Professor Anders Biel from Karlstad University in Sweden and the Swedish company Lamera from...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Symposium on Functional Materials for Electrolysis, Fuel Cells and Metal-Air Batteries

02.10.2019 | Event News

NEXUS 2020: Relationships Between Architecture and Mathematics

02.10.2019 | Event News

Optical Technologies: International Symposium „Future Optics“ in Hannover

19.09.2019 | Event News

 
Latest News

New deep-water coral discovered

22.10.2019 | Life Sciences

DNA-reeling bacteria yield new insight on how superbugs acquire drug-resistance

22.10.2019 | Life Sciences

Heat Pumps with Climate-Friendly Refrigerant Developed for Indoor Installation

22.10.2019 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>