Scientific Events

Transition metal oxide superlattices have been widely investigated during recent years as they are one of the largest material groups where physical and chemical properties such as ferroelectricity, magnetism, ionic and electronic conductivity are closely coupled to structural parameters. Cation sub¬sti¬tution in complex oxides is an effective way to develop the functionalities through carrier doping, band engineering, or application of chemical pressure. For example, the coupling between charge and spin degrees of freedom across the interfaces and the local charge carrier concentration profiles have profound influences on the occurrence of superconductivity in low dimensional systems. Super-conductivity arises when a parent insulator compound is doped beyond some critical con-centration. Furthermore, the magnetic behaviour and conductivity of complex oxide superlattices can be tuned by controlling the layer thickness and by selecting appropriate intervening layer materials. Various methods for growing controlled superlattice structures exist, a favourite has been pulsed laser deposition (PLD), but molecular beam epitaxy (MBE) is now also popular because of the controlled deposition rate and the flexibility allowed by the use of individual element sources. In theory, this allows composition control to the level of individual atomic layers. The PLD process requires higher temperatures and pressures than MBE. It also involves significantly higher energies for the impinging particles, which has potential implications for the interface roughness. In this presentation, I will discuss mapping of the local structure and interfacial chemistry of various complex oxide hetero-interfaces through advanced scanning transmission electron microscopy (STEM) in combination with energy-dispersive x-ray (EDX) analysis and electron energy-loss spectroscopy (EELS).1 EELS allows for local probing of chemical composition and bonding, as well as electronic and magnetic structure, making the combination of STEM and EELS ideal for discovery of structure-property correlations at the atomic scale.2,3 References 1 F. Baiutti et al., Nature Comm. (2015), DOI: 10.1038/ncomms9586, in press. A.V. Boris et al., Science 332 (2011) 937-940. E. Detemple et al., Appl. Phys. Lett. 99 (2011) 211903. E. Detemple et al., J. Appl. Phys. 112 (2012) 013509. A. Frano et al., Adv. Mater. 26 (2014) 258-262. F. Wrobel et al., submitted (2015). K. Song et al., APL Materials 2 (2014) 032104. D. Zhou et al., APL Materials 2 (2014) 127301. D. Zhou et al., Adv. Mater. Interfaces 2 (2015) 1500377. D. Zhou et al., Ultra¬micro¬sco¬py 160 (2016) 110–117. 2 PAvA gratefully acknowledges the intense collaboration with the following people without their contributions this work wouldn’t have been possible: F. Baiutti, E. Benckiser, C. Bernhard, A.V. Boris, M. Castro-Colin, G. Cristiani, E. Detemple, K. Du, A. Frano, E. Gilardi, G. Gregori, H.-U. Habermeier, V. Hinkov, B. Keimer, M. Kelsch, F.F. Krause, G. Logvenov, Y. Lu, J. Maier, V.K. Malik, A.F. Mark, Y. Matiks, M. Morenzoni, K. Müller-Caspary, E. Okunishi, P. Popovich, T. Prokscha, Q.M. Ramasse, M. Reehuis, A. Rosenauer, Z. Salman, H. Schmid, W. Sigle, K. Song, V. Srot, A. Suter, Y. Wang, P. Wochner, F. Wrobel, M. Wu, D. Zhou. 3 The research leading to these results has received funding from the European Union Seventh Framework Program [FP/2007/2013] under grant agreement no 312483 (ESTEEM2). [more]

In modern society, metallic materials are crucially important (e.g. for applications related to energy, safety, infrastructure, transportation, health, medicine, life sciences, IT). Contemporary examples with inherent challenges to be overcome are the design of ultrahigh specific strength materials. There is a critical need for successful developments in this area in particular for reduced energy consumption, reduction of pollutant emissions and passenger safety. Also, the ageing society makes biomedical materials for implant and stent design crucially important. A drawback of nearly all current high strength metallic materials is that they lack ductility (i.e. are brittle and hard to form) - or on the opposite side, they may be highly ductile but lack strength. Hence, it is mandatory to develop new routes for creation of tailored metallic materials based on hierarchical hybrid structures enabling property as well as function optimization. One starting point along these lines is the design of monolithic amorphous materials or bulk micro-, ultrafine- or nano-structured composite structures with intrinsic length-scale modulation and phase transformation under highly non-equilibrium conditions. This can include the incorporation of dispersed phases which are close to or beyond their thermodynamic and mechanical stability limit thus forming hierarchically structured hybrid and ductile/tough alloys. Alternatively, the material itself can be designed in a manner such that it is at the verge of its thermodynamic/mechanical stability. This talk will present recent results obtained for metallic glass-based hybrid structures with transformation effects at different length-scales and microcrystalline-grained hybrid structures based on elastic instabilities and modulated length-scale. The deformation behaviour and possible phase transitions during deformation will be related to the intrinsic properties of the phases as well as the microstructure of the material including heterogeneities and length-scale modulation in order to derive guidelines for the design of macroscopically ductile high-strength materials. Finally, the results will be critically assessed from the viewpoint of possible scaling-up for technological applications and the use of simple and cost effective processing technologies. [more]