“Green” chemistry

In mechanochemistry, reagents are finely ground and mixed so that they combine to form the desired product, even without need for solvent. By eliminating solvent, this technology promises to contribute significantly towards ‘green’ and environmentally benign chemical manufacture in the future. However, there are still major gaps in understanding the key processes that occur during mechanical treatment and reaction. A team led by the Federal Institute for Materials Research (BAM) has now developed a method at BESSY II to observe these processes in situ with X-ray scattering.

Chemical reactions are often based on the use of solvents that pollute the environment. Yet, many reactions can also work without solvent. This is the approach known as mechanochemistry, in which reagents are very finely ground and mixed together so that they react with each other to form the desired product.  The mechanochemical approach is not only more environmentally friendly, but even potentially cheaper than classical synthesis methods. The International Union of Pure and Applied Chemistry (IUPAC) therefore ranks mechanochemistry among the 10 chemical innovations that will change our world. However, the full potential of this technology cannot be realized until the processes during mechanical treatment are understood in more detail, so that it is possible to precisely direct and control them.

Read more on the HZB website

Image: Finely ground powders can also react with each other without solvents to form the desired product. This is the approach of mechanochemistry.

Credit: © F. Emmerling/BAM

Dramatic impact of crystallographic conflict on material properties

Many material properties are associated with structural disorder that exhibits local periodicity or correlations. A new form of this phenomenon exhibiting strong disorder-phonon coupling has been shown to arise in response to crystallographic conflict, with dramatic phonon lifetime suppression.

In recent years there has been a rapidly growing understanding that, hidden within the globally periodic structures of many crystals, various forms of disorder may exist that could form ‘locally periodic’ states, which the language of classic crystallography fails to describe. Such phenomena are commonly referred to as ‘correlated disorder’ and in many functional materials, from leading ferroelectric and thermoelectric candidates to photovoltaic perovskites and ionic conductors, this correlated deviation from perfect periodicity plays a pivotal role in governing functionality. As such, understanding the role of disorder, and the correlations that exist within it, is one of the defining challenges for the development of future functional materials.

Read more on the ESRF website

Image: Fig. 1: a) Reciprocal space reconstructions of the (hk2)s plane. All three samples investigated are shown with relevant at. % Mo indicated. Reflections are categorised and indexed in the bottom right quadrant, parent Bragg peaks (black) and diffuse superstructure reflections from two different domains (blue/green). b) Orientational relationship between parent (blue) and superstructure (red) unit cells for one of six possible domains. All atoms in the “shear plane” (highlighted red) move collinearly with the direction of motion indicated by arrows on the plane edge. Alternate planes, demarcated by I, I, III, … , move in antiphase. c) Top-down view showing the 45 relationship between the parent and superstructure. d) Schematic of the atomic motions in a “phonon plane.” Blue dashed and red dotted lines refer to interatomic bonding in the parent and superstructure unit cells, respectively.

Physicists uncover secrets of world’s thinnest superconductor

Physicists report the first experimental evidence to explain the unusual electronic behaviour behind the world’s thinnest superconductor, a material with myriad applications because it conducts electricity extremely efficiently. In this case the superconductor is only an atomic layer thick. 

The research, led by Massachusetts Institute of Technology and Brookhaven National Laboratory, was possible thanks to new instrumentation available at Diamond.  

Diamond is one of only a few facilities in the world to use the new experimental technique, Resonant Inelastic X-ray Scattering (RIXS), which is a combination of X-ray Absorption Spectroscopy (XAS) and X-ray Emission Spectroscopy (XES), where both the incident and emitted energies are scanned. This state-of-the-art facility is where the team from three continents conducted their experiment.  

Read more on the Diamond website

Image: Members of the RIXS team at Diamond. Left to right: Jaewon Choi (Postdoc), Abhishek Nag (Postdoc), Mirian Garcia Fernandez (Beamline Scientist), Charles Tam (joint PhD student), Thomas Rice (Beamline technician), Ke-Jin Zhou (Principal Beamline Scientist), Stefano Agrestini (Beamline Scientist).

Strong and resilient synthetic tendons produced from hydrogels

Human tissues exhibit a remarkable range of properties. A human heart consists mostly of muscle that cyclically expands and contracts over a lifetime. Skin is soft and pliable while also being resilient and tough. And our tendons are highly elastic and strong and capable of repeatedly stretching thousands of times per day. While limited success has been achieved in producing man-made materials that can mimic some of the properties of natural tissues (for instance polymers used as synthetic skin for wound repair) scientists have failed to create artificial materials that can match all the outstanding features of tendons and many other natural tissues. An international team of researchers has transformed a standard hydrogel into an artificial tendon with properties that meet and even surpass those of natural tendons. This new material was examined via electron microscopy and x-ray scattering to reveal the microscopic structures responsible for its outstanding features. The x-ray measurements were gathered at the U.S. Department of Energy’s (DOE’s) Advanced Photon Source (APS). The researchers have shown that their new hydrogel-based material can be modified to mimic a variety of human tissues and could also potentially be adapted to non-biological roles. Their results were published in the journal Nature.

Read more on the APS website

Image: Fig. 1. SEM images (left) showing the deformation of the mesh-like nanofibril network during stretching and corresponding in situ SAXS patterns (right). Scale bars, 1 μm (SEM images); 0.025 Å−1 (SAXS images)

Credit: From M. Hua et al., Strong tough hydrogels via the synergy of freeze-casting and salting out,” Nature 590, 594 (25 February 2021). © 2021 Springer Nature Limited

Shedding light on the causes of arsenic contamination

An international team has used the Canadian Light Source at the University of Saskatchewan to uncover the elusive structure of two arsenic-containing compounds, information that can be used to prevent and predict arsenic contamination.

Arsenic occurs naturally in the environment, and it is present in ore deposits and the waste left behind by mining for gold, uranium, and other metals. The concern with arsenic-containing compounds, like yukonite and arseniosiderite, is that soil sources can find their way into waterways. Understanding how this happens on a structural level can help scientists — and industry — better understand how the two are formed and better protect the surrounding environment from potential arsenic contamination.

Discovered more than 100 years ago, yukonite and arseniosiderite, which are compounds of arsenic, calcium, iron and oxygen, have concealed their structure from scientists thanks to their low crystallinity. While it’s relatively easy to determine the structure of materials that have a high degree of crystallinity, because of the complexity in the way these minerals’ atoms are arranged, usual methods have come up short in painting a clear picture of their structure.

Using a special technique at the CLS called the pair distribution function (PDF), an international team of researchers from Canada, China, the USA, Italy, and Ireland was able to visualize for the first time how atoms are structured in samples of arseniosiderite, which is classified as semi-crystalline, and yukonite, which is considered a nano-crystalline mineral.

Read more on the CLS website

 Image: Specimen BM.62813 from the collections of the Natural History Museum, London 

Credit: © The Trustees of the Natural History Museum, London