Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Disorder plays a key role in phase transitions of materials

05.11.2018

Phase transitions are common occurrences that dramatically change the properties of a material, the most familiar being the solid-liquid-gas transition in water. Each phase corresponds to a new arrangement of the atoms within the material, which dictate the properties of the substance.

While these arrangements can be easily studied in each phase individually, it is significantly harder to study how they change their arrangements from one state to the other during a phase transition.


This is a schematic illustration of the Vanadium Dioxide atomic structure.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

This is because atoms are incredibly small, and the distances by which they move are correspondingly tiny and, as a result, they can occur very quickly. Furthermore, materials consist of over 1023 atoms, making it extremely challenging to track their individual motions.

One particularly intriguing phase change is the insulator-metal transition in the material Vanadium Dioxide (VO2). At room temperature VO2 is an insulator, and inside the crystal, the vanadium ions form periodic chains of vanadium pairs, known as dimers.

When this compound is heated to just above room temperature, the atomic structure changes and the pairs are broken, but the material remains a solid. At the same time, the conductivity of the material increases by over 5 orders of magnitude and has a diverse range of applications from energy-free climate control to infrared sensing.

One of the intriguing properties of VO2 is that the phase transition can occur incredibly rapidly with the only limit appearing to be how fast you can heat the system. In order to explain this incredible speed, scientists suggested that there must be cooperative motion between the vanadium ions, i.e. each vanadium pair breaks in the same way at the same time.

In order to understand atomic structure of materials, scientists use a technique known as diffraction. Over the past 30 years, this method has been extended to include time resolution, with the goal of obtaining the "molecular movie", i.e. to directly film the motion of the atoms during the transition. When this technique was first applied to VO2 in 2007, it seemed to confirm the picture of coordinated motion.

However, diffraction only measures the average atomic position and reveals little information about the actual path taken by the individual atoms involved. For example, protestors marching down the avenue Passeig de Gràcia in Barcelona move in a uniform, regular coordinated fashion, whereas a group of tourists may cover the same distance, on average, but in a completely uncoordinated fashion, wondering around and randomly halting to look at the architecture of the city. In diffraction, these processes would look the same.

Now, in a recent study, published in Science, ICFO researchers Prof. Simon Wall, PhD student Luciana Vidas and former post doc Timothy miller, in collaboration with scientists from Duke University, SLAC National Accelerator Laboratory, Japan Synchrotron Radiation Research Institute, Stanford University and Oak Ridge National Laboratory have used a new technique that is capable of resolving the atomic pathways.

To do this the researchers made use of the world's first X-ray laser situated in the SLAC National Accelerator Laboratory. This new light source enabled researchers to examine the crystal structure with unprecedented details using a technique known as total X-ray scattering. In contrast to the prevailing view, the authors found that the break-up of the vanadium pairs was extremely disorderly and more like the tourists, than the marchers.

As Simon Wall, first author of the paper comments "This is the first time we have really been able to observe how atoms re-arrange in a phase transition without assuming the motion is uniform and suggests that the text book understanding of these transitions needs to be re-written. We now plan to use this technique to explore more materials to understand how wide-spread the role of disorder is".

To date, VO2 has often been used as a guide for understanding the phases in more complex materials such as high temperature superconductors. Thus the lessons learnt here suggest that these materials will also need to be re-examined. Furthermore, understanding the role of disorder in vibrational materials could imply a new perspective on how to control matter, especially in the field of superconductivity, which could have major implications for nano-technology and optoelectronics.

###

Reference: Simon Wall, Shan Yang, Luciana Vidas, Matthieu Chollet, James M. Glownia, Michael Kozina, Tetsuo Katayama, Thomas Henighan, Mason Jiang, Timothy A. Miller, David A. Reis, Lynn A. Boatner, Olivier Delaire, Mariano Trigo, 2018, Science, Vol. 362, Issue 6414, pp. 572-576, DOI: 10.1126/science.aau3873 (http://science.sciencemag.org/content/362/6414/572.editor-summary)

Link to the research group led by ICFO Prof. Simon Wall: https://www.icfo.eu/lang/research/groups/groups-details?group_id=36

Media Contact

Alina Hirschmann
alina.hirschmann@icfo.eu
34-935-542-246

http://www.icfo.es 

Alina Hirschmann | EurekAlert!

Further reports about: Photonic VO2 X-ray scattering atomic structure ions vanadium ions

More articles from Materials Sciences:

nachricht Shell increases versatility of nanowires
26.06.2019 | Helmholtz-Zentrum Dresden-Rossendorf

nachricht Crystal with a twist: Scientists grow spiraling new material
21.06.2019 | University of California - Berkeley

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fraunhofer IDMT demonstrates its method for acoustic quality inspection at »Sensor+Test 2019« in Nürnberg

From June 25th to 27th 2019, the Fraunhofer Institute for Digital Media Technology IDMT in Ilmenau (Germany) will be presenting a new solution for acoustic quality inspection allowing contact-free, non-destructive testing of manufactured parts and components. The method which has reached Technology Readiness Level 6 already, is currently being successfully tested in practical use together with a number of industrial partners.

Reducing machine downtime, manufacturing defects, and excessive scrap

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

Im Focus: The hidden structure of the periodic system

The well-known representation of chemical elements is just one example of how objects can be arranged and classified

The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Shell increases versatility of nanowires

26.06.2019 | Materials Sciences

Hubble finds tiny 'electric soccer balls' in space, helps solve interstellar mystery

26.06.2019 | Physics and Astronomy

New combination therapy established as safe and effective for prostate cancer

26.06.2019 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>