Scientific Events

Mechano-catalytic depolymerization of plastic waste

MPI SusMat Colloquium
  • Date: Jun 27, 2024
  • Time: 11:00 AM - 01:00 PM (Local Time Germany)
  • Speaker: Prof. Ina Vollmer
  • Inorganic Chemistry and Catalysis research group, Utrecht University
  • Location: Max-Planck-Institut für Nachhaltige Materialien GmbH
  • Room: Large Conference Room No. 203 / Online
Only 12% of plastic waste is recycled, mainly because the predominantly applied technique of melting and re-extrusion produces a lower quality material [1]. Alternatively, chemical depolymerization can produce monomers to make high-quality plastics again. [more]

Hydrogen effects on the deformation and fracture of alloys

MPI SusMat Colloquium
  • Date: Jun 18, 2024
  • Time: 05:00 PM - 07:00 PM (Local Time Germany)
  • Speaker: Prof. Christian Motz
  • Head of Chair of Experimental Methods in Material Science, Department of Material Science and Technology, Saarland University
  • Location: Max-Planck-Institut für Nachhaltige Materialien GmbH
  • Room: Large Conference Room No. 203 / Online
  • Host: on invitation of Prof. Gerhard Dehm
The increasing demand on lightweight structures requires high-strength materials. However, with increasing strength many materials show an increasing susceptibility to hydrogen embrittlement. Hence, it is of vital interest to understand the mechanisms of hydrogen embrittlement. [more]

Designing thermoelectric chalcogenides with atom probe tomography

  • Date: Jun 18, 2024
  • Time: 03:30 PM - 04:30 PM (Local Time Germany)
  • Speaker: Yuan Yu
  • Institute of Physics (IA), RWTH Aachen University, 52074 Aachen, Germany
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Large Conference Room No. 203
  • Host: on invitation of Dr. Siyuan Zhang / Prof. Christina Scheu
Thermoelectric materials can realize waste heat recovery and solid-state refrigeration, providing sustainable solutions to the energy crisis and environmental pollution. The performance of thermoelectric materials is gauged by the transport of electrons and phonons. Materials with fast electron movement but slow phonon propagation would be ideal thermoelectrics. These transport behaviors of carriers are influenced by the intrinsic chemical bonding mechanism and structural defects of materials. Understanding the bonding and microstructures of materials is of paramount importance to improve their thermoelectric properties. Atom probe tomography (APT) provides a unique combination of characterizing chemical bonding and lattice defects, being a very powerful tool in the study of thermoelectric materials. It has been revealed that many of the high-performance thermoelectric chalcogenides utilize metavalent bonding (MVB), which can be distinguished from other bonding mechanisms by the unconventionally high value (>60%) of “probability of multiple events (PME)” measured by APT. Thus, many new compounds with high thermoelectric performance can be designed by tailoring their chemical bonds, and APT is an indispensable technique to corroborate the bonding transition. Owing to the high spatial and chemical resolution of APT, the local change of chemical bonding at defects such as grain boundaries and precipitates can also be detected by APT. This enables us to better understand the role of chemical bonding in regulating the electron and phonon transport across individual defects. The results in turn provide insights into the tailoring of thermoelectric properties by manipulating the local chemical bonds. For example, the thermoelectric properties of polycrystalline SnSe have been significantly improved by removing the stiff Sn-O bonds at the grain boundary as directly observed by APT. In contrast, the strong bonding connection between thermoelectric and interfacial materials enables a high-efficiency and durable thermoelectric device. Based on APT, in conjunction with other characterization techniques, we can explore some uncharted territories in the design of thermoelectric materials. [more]

Defects and Grain Boundary Effects on Thermal and Electrical Transport

  • Date: Jun 18, 2024
  • Time: 02:30 PM - 03:30 PM (Local Time Germany)
  • Speaker: G Jeffrey Snyder
  • Northwestern University, Evanston IL, USA
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Large Conference Room No. 203
  • Host: on invitation of Dr. Siyuan Zhang / Prof. Christina Scheu
Defects and Grain boundaries have a remarkable effect on the thermal and electrical transport properties of polycrystalline materials but are often ignored by prevailing physical theories. Grain boundaries and interfaces can adversely alter the properties of Power Electronics, Solar Cells, Batteries and Thermoelectrics such as interfacial electrical and thermal resistance (Kapitza resistance) and even an interfacial Seebeck effect. Interfacial thermal resistance limits the performance of power electronics because of overheating. New scanning thermal reflectance techniques can image the thermal resistance of interfaces and boundaries directly. The Thermal conductivity suppression at grain boundaries can even be imaged showing that different grain boundaries can have very different thermal resistances with high energy grain boundaries having more resistance and low energy boundaries having lower thermal resistance. Electrical grain boundary resistance can be so high in some thermoelectric materials it is the dominant property that limits zT. While small grains are usually considered beneficial for thermoelectric performance due to reduced thermal conductivity, Mg₃Sb₂ based thermoelectric materials, so far at least, contradict that trend. Indeed, atomic segregation has been recently observed at the nanometer scale in grain boundaries in many materials suggesting interfacial or complexion phases should be specifically considered when understanding nearly all thermoelectric materials. The concentration of point defects, such as vacancies, interstitial and substitutional atoms can now be predicted with DFT allowing defects to be included in phase diagram analysis for prediction of materials processing for particular properties. [more]

Materials grown by electrochemical techniques: The route towards sustainable materials for energy

  • Date: Jun 7, 2024
  • Time: 11:00 AM - 12:00 PM (Local Time Germany)
  • Speaker: Dr. Cristina Vicente Manzano
  • Spanish National Research Council (CSIC)
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Large Conference Room No. 203
  • Host: on invitation of Dr. James Best and Prof. Gerhard Dehm
In recent decades, extensive efforts have been done to develop new and more efficient alternative energy sources, which can substitute conventional sources like gas, petrol, and carbon, have been made. Due to the increase in energy consumed by society, we not only need an alternative to conventional energy sources, but also a reduction in energy consumption. Therefore, it is necessary to investigate different methods for energy-recovery and energy-saving as such as thermoelectric materials and radiative coolers. The thermoelectric materials can convert heat into electricity and vice versa. The efficiency of these materials is related to the figure of merit (zT) and it is defined as zT=(σ·S2/k)·T, where σ is the electrical conductivity, S is the Seebeck coefficient, k is the thermal conductivity, and T is the absolute temperature. Nowadays, the application of inexpensive and scalable materials in the industry for thermoelectric applications has received great interest. In this sense electrodeposition is one of the most interesting techniques. It is performed at room temperature, so it is compatible with polymeric substrates, it does not require vacuum conditions, and it allows perfect control over the composition, morphology, and crystallographic structure. In this presentation, I will provide an overview of different thermoelectric materials such as Bi2Te31, CuNi2, and Ag2Se3 grown by electrodeposition and their thermoelectric properties. In the case of silver selenide, a thermoelectric power generator was produced and characterized. Radiative cooling is the process by which temperature decreases due to an excess of emitted radiation above absorber radiation. To achieve cooling, it is necessary to reduce and keep the temperature below the ambient air temperature. The requirements of radiative coolers to have maximum cooling power, to be able to reduce the temperature sufficiently, and to function 24 hours a day anywhere, are high solar reflectance and high infrared emittance, close to the atmosphere’s window (between 8 and 13μm wavelengths). Different approaches have been explored and porous nanostructures have shown the best results to this respect. In this sense, porous anodic aluminium oxide (AAO) nanostructures on Al was demonstrated to be a great candidate4. AAO is an amorphous material with an isotropic permittivity, a strong acoustic resonance absorption at the far IR (15 – 25 µm), and high transparency in the UV‑Vis‑NIR range. In this presentation, I will highlight the possibilities to use AAO nanostructure as radiative cooling. In addition, strcutural cellulose will be also analysed for the same purpose. [more]

H in thin films: size and stress effects on the system thermodynamics and kinetics

MPIE Colloquium
  • Date: Apr 23, 2024
  • Time: 03:00 PM (Local Time Germany)
  • Speaker: Prof. Dr. rer. nat. Astrid Pundt
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Big Seminar Room / Online
  • Host: on invitation of Prof. Gerhard Dehm
Due to its high diffusivity hydrogen atoms alloy with metals even at room temperature. At this temperature, the materials microstructure remains rather stable. When the system size is reduced to the nano-scale, microstructural defects as well as mechanical stress significantly affect the thermodynamics and kinetics properties of the system.[1-6] Effects will be demonstrated on Niobium-H and Palladium-H thin films.Hydrogen absorption in metal systems commonly leads to lattice expansion. The lateral expansion is hindered when the metal adheres to a rigid substrate, as for thin films. Consequently, high mechanical stresses arise upon hydrogen uptake. In theory, these stresses can reach about -10 GPa for 1 H/M. Usually, metals cannot yield such high stresses and deform plastically. Thereby, maximum compressive mechanical stress of -2 to -3 GPa is commonly measured for 100 nm Nb thin films adhered to Sapphire substrates. It will be shown that phase transformations change in the coherency state upon film thickness reduction. The coherency state affects the nucleation and growth behaviour of the hydride phase as well as the kinetics of the phase transformation.[1] It will be further demonstrated that plastic deformation can be hindered and even suppressed upon film thickness reduction. In this case the system behaves purely elastic and ultra-high stress of about -10 GPa can be experimentally reached.[2] These high mechanical stresses result in changes of the materials thermodynamics. In the case of Nb-H thin films of less than 8 nm thickness, the common phase transformation from the α-phase solid solution to the hydride phase is completely suppressed, at 300 K.[3,4,5] The experimental results go in line with the σDOS model that includes microstructural and mechanical stress effects on the chemical potential [6]. [1] V. Burlaka, K. Nörthemann, A. Pundt, „Nb-H Thin Films: On Phase Transformation Kinetics“, Def. Diff. Forum 371 (2017) 160. [2] M. Hamm, V. Burlaka, S. Wagner, A. Pundt, “Achieving reversibility of ultra-high mechanical stress by hydrogen loading of thin films”, Appl. Phys. Letters 106 (2015) 243108. [3] S. Wagner, A. Pundt, “Quasi-thermodynamic model on hydride formation in palladium-hydrogen thin films: Impact of elastic and microstructural constraints “, Int. J. Hydrog. Energy 41 (2016) 2727. [4] V. Burlaka, S. Wagner, M. Hamm, A. Pundt, “Suppression of phase transformation in Nb-H thin films below switchover-thickness”, Nano Letters 16 (2016) 6207. [5] S. Wagner, P. Klose, V. Burlaka, K: Nörthemann, M. Hamm, A. Pundt, Structural Phase Transitions in Niobium Hydrogen Thin Films: Mechanical Stress, Phase Equilibria and Critical Temperatures, Chem. Phys. Chem. 20 (2019) 1890–1904. [6] S. Wagner, A. Pundt, Hydrogen as a probe for defects in materials: Isotherms and related microstructures of palladium-hydrogen thin films, AIMS Materials Science 7 (2020), 399–419. [more]

Sustainability and raw materials: do we have them enough?

  • Date: Apr 18, 2024
  • Time: 01:15 PM - 02:15 PM (Local Time Germany)
  • Speaker: Dr. Janez Zavašnik
  • Jozef Stefan Institute, Ljubljana, Slovenia; MPIE-SN External Group Leader
  • Location: Max-Planck-Institut für Eisenforschung GmbH
  • Room: Large Conference Room No. 203
  • Host: on invitation of Dr. Jazmin Duarte and Prof. Gerhard Dehm
Materials play a crucial role in driving the twin transition, a key strategy of the European Union to address current and future environmental challenges. Currently, improving the efficiency of solar cells and the capacity of battery storage is essential for achieving a Net Zero Carbon society, underlining the growing demand for innovative materials. Nanotechnology played a major role in development of the necessary hardware, such as sensors, data storage systems, and actuators, needed for advanced digital solutions. Still, the push to enhance performance and replace outdated technologies is accelerating the research into always-new materials and solutions. Performance-oriented development also expanded the range of metals utilized by humanity, leading to a scenario where a single smartphone necessitates a broader spectrum of elements than the entire biosphere [1], [2]. Due to the fast development, the raw materials for such technologies are changing by day - a pace that the supply chain cannot follow satisfactory. In addition, the environmental impact of raw materials production, especially metals, varies significantly. For example, steel production—accounting for 1.9 billion tons annually—contributes to 8% of global CO2 emissions, but its per mass environmental footprint is one of the lowest (2 kg of CO2 per kg of primary steel, and 0.7 kg of CO2 when recycled). In contrast, the production of platinum, crucial element for hydrogen economy with a limited production of 200 t/y, is one of the most carbon-intensive (60 tons of CO2 per kg of Pt). Limiting the challenge of the Green and digital revolutions to the simple cost-performance paradigm would be somehow repeating the mistake of the Oil Age during which the resource was considered as infinite and the impact on the environment had been long time neglected. Making the twin transition successful requires changing the mindset of innovators (from lower TRL) to a binary trade-off (price-performance) towards multi-criteria decision-making [3]. In the presentation, we will introduce a straightforward multi-criteria assessment methodology for evaluating the sustainability of metallic alloys. [more]
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