Invited speakers:

Prof. Dr. Oliver Diwald / Paris-Lodron University Salzburg
"Intergranular Chemistry and Sintering of Metal Oxide Particle Powders"

Ass.Prof. Markus Kubicek / Technical University Vienna
"Mass and Charge Transport in Mixed Ionic Electronic Conductors"



Abstract - "Intergranular Chemistry and Sintering of Metal Oxide Particle Powders"

Oliver Diwald, Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Straße 2a, A-5020 Salzburg, Austria

Configurations of composite metal oxide nanoparticles are typically far off their thermodynamic equilibrium state. As such they represent a versatile but so far overlooked source material for the intergranular solid-state chemistry inside ceramics. Moreover, Ion exsolution can be instrumental to engineer intergranular regions inside ceramic microstructures that are derived from nanocomposites. We explored the potential of vapor phase-grown MgO nanoparticles hosting Ba2+, In3+ and Fe3+ admixtures as precursors for engineered intergranular regions.[1,2]

During annealing-induced exsolution from the nanocrystal bulk into the grain interfaces, the impurity admixtures impact grain coarsening and powder densification, effects that were compared for the first time using an integrated characterization approach. The comprehensive structural analysis with XRD and electron microscopy enabled us to draw conclusions on the structure-property-relationships that are controlled by the impurity dispersion inside the MgO grain network.

Depending on the concentration of admixed Ba2+ ions, isolated impurity ions either become part of low-coordinated surface structures of the MgO grains where they give rise to a characteristic bright photoluminescence emission profile around λ = 500 nm, or they aggregate to form nanocrystalline BaO segregates at the inner pore surfaces to produce an emission feature centered at λ = 460 nm.[3]

A substantially less soft magnetic behavior was observed for samples with iron admixtures and a reduced fraction of the intergranular MgFe2O4 phase. Respective phenomenon is attributed to a nanodispersion effect describing size-dependent magnetic properties of Fe3+-doped MgO ceramics. Percolating networks of semiconducting MgIn2O4 were derived from MgO nanoparticles with admixtures of 20 at% In3+ that gives rise to an enhancement of dc conductivity values by more than 5 orders of magnitude in comparison to the insulating host.

The here presented approach is general and applicable to the synthesis of a variety of functional nanostructured spinel structures embedded inside ceramic matrices. Densification of vapor phase-grown nanoparticle powders with extremely well-defined bulk and surface properties to generate ceramics can lead to a high abundance of structurally and compositionally uniform intergranular regions that emerge from the interrelated effects of segregation and grain growth.

[1] Schwab, T.; Razouq, H.; Aicher, K.; Zickler, G. A.; Diwald, O.;, 106 (2023) 897; doi.org/10.1111/jace.18833.
[2] Schwab T. et al.; ACS Appl. Mater. Interfaces 13 (2021) 25493; doi.org/10.1021/acsami.1c02931.
[3] Aicher K., Schwab, T. et al. to be submitted (2024)



Abstract - "Mass and Charge Transport in Mixed Ionic Electronic Conductors"

Markus Kubicek, Institute of Chemical Technologies and Analytics, TU Wien, Getreidemarkt 9, 1060 Wien, Austria

Mixed ionic electronic conductors (MIECs) are materials that combine semiconducting and ionic properties. Their functionality relies on mobile electronic charge carriers (electrons/holes), and mobile ions (cations, anions, vacancies) and their reactivity at surfaces and interfaces. As functional ceramics, MIECs are the centerpiece of many important devices and applications particularly in the field of energy conversion and storage. They allow efficient conversion of chemical to electric energy and back in solid oxide fuel and electrolysis cells (SOFC, SOEC), in lithium ion batteries (LIB) they enabled today’s use of portable devices and e-mobility. They are also the active component for thermochemical solar-to-fuel conversion or may even be used as memristive nonvolatile memories.

Equally important to understanding the functionality of MIEC materials are their bulk (where defect thermodynamics can be used to describe MIECs) and their surfaces and interfaces (where electrostatic, elastic effects or sub-nm segregation or impurity phases may dominate material properties). Several examples of my research activity on MIEC materials for above topics are presented, highlighting new in-situ approaches for gaining knowledge on materials, mechanisms and device functionality. Thin films of 5-100 nm thickness are of particular interest for these tasks, since they offer unique opportunities to investigate and manipulate materials in terms of structure, composition or elastic properties.