Home > Press > Scientists discover new class of semiconducting entropy-stabilized materials

Crystal structure of GeSnPbSSeTe, a semiconducting entropy-stabilized chalcogenide alloy. The yellow atoms are cations (Ge, Sn, Pb) and the blue atoms are anions (S, Se, Te). The difference in lightness corresponds to different species of the anions and cations. The configurational entropy from the disorder of both the anion and the cation sublattices stabilizes the single-phase rocksalt solid solution, as demonstrated from first-principles calculations as well as experimental synthesis and characterization. CREDIT Logan Williams, Emmanouil Kioupakis, and Zihao Deng, Dept. of Materials Science & Engineering, University of Michigan

Abstract:
Semiconductors are important materials in numerous functional applications such as digital and analog electronics, solar cells, LEDs, and lasers. Semiconducting alloys are particularly useful for these applications since their properties can be engineered by tuning the mixing ratio or the alloy ingredients. However, the synthesis of multicomponent semiconductor alloys has been a big challenge due to thermodynamic phase segregation of the alloy into separate phases. Recently, University of Michigan researchers Emmanouil (Manos) Kioupakis and Pierre F. P. Poudeu, both in the Materials Science and Engineering Department, utilized entropy to stabilize a new class of semiconducting materials, based on GeSnPbSSeTe high-entropy chalcogenide alloys,[1] a discovery that paves the way for wider adoption of entropy-stabilized semiconductors in functional applications. Their article, “Semiconducting high-entropy chalcogenide alloys with ambi-ionic entropy stabilization and ambipolar doping” was recently published in the journal Chemistry of Materials.

Scientists discover new class of semiconducting entropy-stabilized materials

Ann Arbor, MI | Posted on July 31st, 2020

Entropy, a thermodynamic quantity that quantifies the degree of disorder in a material, has been exploited to synthesize a vast array of novel materials by mixing eachcomponent in an equimolar fashion, from high-entropy metallic alloys to entropy-stabilized ceramics. Despite having a large enthalpy of mixing, these materials can surprisingly crystalize in a single crystal structure, enabled by the large configurational entropy in the lattice. Kioupakis and Poudeu hypothesized that this principle of entropy stabilization can be applied to overcome the synthesis challenges of semiconducting alloys that prefer to segregation into thermodynamically more stable compounds. They tested their hypothesis on a 6-component II-VI chalcogenide alloy derived from the PbTe structure by mixing Ge, Sn, and Pb on the cation site, and S, Se, and Te on the anion site.

Using high throughput first-principles calculations, Kioupakis uncovered the complex interplay between the enthalpy and entropy in GeSnPbSSeTe high-entropy chalcogenide alloys. He found that the large configurational entropy from both anion and cation sublattices stabilizes the alloys into single-phase rocksalt solid solutions at the growth temperature. Despite being metastable at room temperature, these solid solutions can be preserved by fast cooling under ambient conditions. Poudeu later verified the theory predictions by synthesizing the e

quimolar composition (Ge1/3Sn1/3Pb1/3S1/3Se1/3Te1/3) by a two-step solid-state reaction followed by fast quenching in liquid nitrogen. The synthesized power showed well-defined XRD patterns corresponding to a pure rocksalt structure. Furthermore, they observed reversible phase transition between single-phase solid solution and multiple-phase segregation from DSC analysis and temperature dependent XRD, which is a key feature of entropy stabilization.

What makes high-entropy chalcogenide intriguing is their functional properties. Previously discovered high-entropy materials are either conducting metals or insulating ceramics, with a clear dearth in the semiconducting regime. Kioupakis and Poudeu found that. the equimolar GeSnPbSSeTe is an ambipolarly dopable semiconductor, with evidence from a calculated band gap of 0.86 eV and sign reversal of the measured Seebeck coefficient upon p-type doping with Na acceptors and n-type doping with Bi donors. The alloy also exhibits an ultralow thermal conductivity that is nearly independent of temperature. These fascinating functional properties make GeSnPbSSeTe a promising new material to be deployed in electronic, optoelectronic, photovoltaic, and thermoelectric devices.

Entropy stabilization is a general and powerful method to realize a vast array of materials compositions. The discovery of entropy stabilization in semiconducting chalcogenide alloys by the team at UM is only the tip of the iceberg that can pave the way for novel functional applications of entropy-stabilized materials.

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This study was supported by the National Science Foundation through Grant No. DMR-1561008 (first-principles calculations, synthesis, and characterization) and the Department of Energy, Office of Basic Energy Sciences under Award # DE-SC-00018941 (electronic and thermal transport measurements). The DFT calculations used resources of the National Energy Research Scientific Computing (NERSC) Center, a DOE Office of Science User Facility supported under Contract No. DE-AC02-05CH11231.Related conference presentation:

Zihao Deng, Alan Olvera, Joseph Casamento, Juan Lopez, Logan Williams, Ruiming Lu, Guangsha Shi, Pierre F. P. Poudeu, and Emmanouil Kioupakis. Computational prediction and experimental discovery of semiconducting high-entropy chalcogenide alloys, MRS Fall Meeting 2019, EL04.01.05

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Contacts:
Emmanouil (Manos) Kioupakis
734-945-4456

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Home > Press > TU Graz researchers synthesize nanoparticles tailored for special applications

The graph illustrates the stepwise synthesis of Silver-Zinc Oxide core-shell clusters. CREDIT © IEP – TU Graz

Abstract:
Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest portions of bulk material – form the basis for a whole range of new technological developments. Due to the laws of quantum mechanics, such particles measuring only a few millionths of a millimetre can behave completely differently in terms of conductivity, optics or robustness than the same material on a macroscopic scale. In addition, nanoparticles or nanoclusters have a very large catalytically effective surface area compared to their volume. For many applications this allows material savings while maintaining the same performance.

TU Graz researchers synthesize nanoparticles tailored for special applications

Graz, Austria | Posted on July 31st, 2020

Further development of top-level research in Graz in the field of nanomaterials

Researchers at the Institute of Experimental Physics (IEP) at Graz University of Technology have developed a method for assembling nanomaterials as desired. They let superfluid helium droplets of an internal temperature of 0.4 Kelvin (i.e. minus 273 degrees Celsius) fly through a vacuum chamber and selectively introduce individual atoms or molecules into these droplets. “There, they coalesce into a new aggregate and can be deposited on different substrates,” explains experimental physicist Wolfgang Ernst from TU Graz. He has been working on this so-called helium-droplet synthesis for twenty-five years now, has successively developed it further during this time, and has produced continuous research at the highest international level, mostly performed in “Cluster Lab 3”, which has been set up specifically for this purpose at the IEP.

Reinforcement of catalytic properties

In Nano Research, Ernst and his team now report on the targeted formation of so-called core-shell clusters using helium-droplet synthesis. The clusters have a 3-nanometer core of silver and a 1.5-nanometer-thick shell of zinc oxide. Zinc oxide is a semiconductor that is used, for example, in radiation detectors for measuring electromagnetic radiation or in photocatalysts for breaking down organic pollutants. The special thing about the material combination is that the silver core provides a plasmonic resonance, i.e. it absorbs light and thus causes a high light field amplification. This puts electrons in an excited state in the surrounding zinc oxide, thereby forming electron-hole pairs – small portions of energy that can be used elsewhere for chemical reactions, such as catalysis processes directly on the cluster surface. “The combination of the two material properties increases the efficiency of photocatalysts immensely. In addition, it would be conceivable to use such a material in water splitting for hydrogen production,” says Ernst, naming a field of application.

Nanoparticles for laser and magnetic sensors

In addition to the silver-zinc oxide combination, the researchers produced other interesting core-shell clusters with a magnetic core of the elements iron, cobalt or nickel and a shell of gold. Gold also has a plasmonic effect and also protects the magnetic core from unwanted oxidation. These nanoclusters can be influenced and controlled both by lasers and by external magnetic fields and are suitable for sensor technologies, for example. For these material combinations, temperature-dependent stability measurements as well as theoretical calculations were carried out in collaboration with the IEP theory group led by Andreas Hauser and the team of Maria Pilar de Lara Castells (Institute of Fundamental Physics at the Spanish National Research Council CSIC, Madrid) and can explain the behaviour at phase transitions such as alloy formation that deviates from macroscopic material samples. The results were published in the Journal of Physical Chemistry.

Ernst now hopes that the findings from the experiments will be rapidly transferred into new catalysts “as soon as possible”.

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This research area is anchored in the Field of Expertise “Advanced Materials Science”, one of five strategic foci of TU Graz. The Cluster 3 laboratory was set up using funds from the European Regional Development Fund (ERDF) with the support of the European Union and the State of Styria. The measurements for photoelectron spectroscopy of the particles could be carried out with the aid of a photoemission electron microscope in the framework of the structural funds of the higher education area of the Austrian Federal Government. The work was also supported by three projects of the Austrian Research Fund FWF.

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Contacts:
Wolfgang ERNST
Em.Univ.-Prof. Dipl.-Phys. Dr.rer.nat.
Tel.: +43 316 873 8140; E-Mail:

Florian LACKNER
Univ.Ass. Dipl.-Ing. Dr.techn.
Tel.: +43 316 873 8647; E-Mail:

Andreas HAUSER
Assoc.Prof. Mag. phil. Dipl.-Ing. Dr. phil Dr. techn.
Tel.: +43 316 873 8157; E-Mail:

At Institute of Fundamental Physics at the Spanish National Research Council CSIC, Madrid:
Maria Pilar de Lara Castells
E-Mail:

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Home > Press > New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home

This tensile object was created using 3D injection printing, a new technology invented by UMass Lowell Plastics Engineering Prof. David Kazmer. CREDIT David Kazmer

Abstract:
More durable prosthetics and medical devices for patients and stronger parts for airplanes and automobiles are just some of the products that could be created through a new 3D printing technology invented by a UMass Lowell researcher.

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home

Lowell, MA | Posted on July 31st, 2020

Substances such as plastics, metals and wax are used in 3D printers to make products and parts for larger items, as the practice has disrupted the prototyping and manufacturing fields. Products created through the 3D printing of plastics include everything from toys to drones. While the global market for 3D plastics printers is estimated at $4 billion and growing, challenges remain in ensuring the printers create objects that are produced quickly, retain their strength and accurately reflect the shape desired, according to UMass Lowell’s David Kazmer, a plastics engineering professor who led the research project.

Called injection printing, the technology Kazmer pioneered is featured in the academic journal Additive Manufacturing posted online last week.

The invention combines elements of 3D printing and injection molding, a technique through which objects are created by filling mold cavities with molten materials. The marriage of the two processes increases the production rate of 3D printing, while enhancing the strength and properties of the resulting products. The innovation typically produces objects about three times faster than conventional 3D printing, which means jobs that once took about nine hours now only take three, according to Kazmer, who lives in Georgetown.

“The invention greatly improves the quality of the parts produced, making them fully dense with few cracks or voids, so they are much stronger. For technical applications, this is game-changing. The new process is also cost-effective because it can be used in existing 3D printers, with only new software to program the machine needed,” Kazmer said.

The process took about 18 months to develop. Austin Colon of Plymouth, a UMass Lowell Ph.D. candidate in plastics engineering, helped validate the technology alongside Kazmer, who teaches courses in product design, prototyping and process control, among other topics. He has filed for a patent on the new technology.

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About University of Massachusetts Lowell
UMass Lowell is a national research university located on a high-energy campus in the heart of a global community. The university offers its more than 18,000 students bachelor’s, master’s and doctoral degrees in business, education, engineering, fine arts, health, humanities, sciences and social sciences. UMass Lowell delivers high-quality educational programs, vigorous hands-on learning and personal attention from leading faculty and staff, all of which prepare graduates to be leaders in their communities and around the globe.

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