Non-stoichiometries in the bulk and at boundaries

The contribution compares non-stoichiometries in the bulk of mixed conductors with the situation at abrupt junctions. While great efforts have really been devoted to optimizing ion conductivity in bulk and boundary zones, much less emphasis is laid on the variation of non-stoichiometry, i.e., of component storage. The general thermodynamic situation including the presence of boundaries is set out by assuming abrupt structural changes at the contacts. Specific examples highlight the significance for oxygen, hydrogen, lithium and silver storage. They comprise oxygen non-stoichiometry in mesoscopic nanocrystalline SrTiO3 as a function of oxygen partial pressure, hydrogen storage and lithium storage in “job-sharing” composites as well as ultrafast silver storage in composites of superion-conductors with graphite or metals

Sociological Cycles: The accumulated discrepancy between appearance and reality as driver

Oscillations are observed in all branches of science and culture, ranging from the behavior of ele-mentary particles, atoms, molecules in simple chemical or physical systems or even in complex organisms, up to oscillations of the behavior of complex organisms such as human beings. Exam-ples of the latter are phenomena as different as waves of public taste, particularly obvious in fash-ion, or periodically repeated surplus or deficiency of qualified jobs in a certain profession. In the focus of the presentation are those cycles that are characterized by periodical sequences of over- and under-estimation (hype cycles). They are not only ubiquitous but also of great impact on and hence of great interest for society. Many of the other oscillation modes, though, can be mapped on this

Stoichiometry effects in bulk and at interfaces: Solid state ionics and beyond

After an introduction on stoichiometric effects in bulk and at boundaries three selected examples are treated that show the relevance not only for Solid State Ionics but also beyond this field. Example 1 gives a full picture of the storage in an electrode material including bulk and boundaries. In this way a unification of electrochemical electrode storage and supercapacitive storage is achieved. Several materials examples are discussed [1-3]. Example 2 refers to photovoltaics. Organic-inorganic hybrid materials show a variety of anomalies at low frequencies and long times that can be explained by mixed conductivity. The nature of the mobile defects in MAPbI3 and their dependence on stoichiometry is discussed. Furthermore, it is shown that the ionic conductivity can be increased by light by two orders of magnitude. This surprising phenomenon paves the way for future light-triggered or light-sensitive Solid State Ionics devices (“opto-ionics”) [4-5]. Example 3 shows the relevance of interfacial effects for superconductivity. By MBE replacing La-O layers atomistically sharply by Sr-O layers a two-dimensional doping is realized resulting in space-charge superconductivity. In this context the strength and weaknesses of zero, one- and two-dimensional doping are considered [6]. [1] C.-C. Chen, J. Maier, Nature Energy, 2018, 3, 102-108. [2] C.-C. Chen., L. Fu, J. Maier, Nature, 2016, 536, 159-164. [3] C. Zhu, R. E. Usiskin, Y. Yu, J. Maier, Science, 2017, 358, eaao2808. [4] A. Senocrate, I. Moudrakovski, G. Y. Kim, T.-Y. Yang, G. Gregori, M. Grätzel, J. Maier, Angewandte Chemie International Edition, 2017, 56, 7755-7759. [5] G. Y. Kim, A. Senocrate, T.-Y. Yang, G. Gregori, M. Grätzel, J. Maier, Nature Materials, 2018, 17, 445-449. [6] F. Baiutti, G. Logvenov, G. Gregori, G. Cristiani, Y. Wang, W. Sigle, P. A. van Aken, J. Maier, Nature Communications, 2015, 6, 8586

How to adequately describe full range intercalation -- a two-sided approach

Here we show the description of the full incorporation thermodynamics in nanocrystalline LixFePO4 where the full range from x=0 to 1 is experimentally accessible. The following points are most important: the treatment in terms of the neutral lattice-gas model is incorrect rather ions and electrons need to be considered separately. One needs to invoke point defect chemistry which gives a satisfactory agreement over the full storage range if we treat the problem from the two-sides: from the FePO4 side where Li+ is incorporated interstitially and from the LiFePO4 side where Li+ is filling the vacancies. Furthermore, we clarify how non-idealities such as ion-electron and electron-electron interactions can be introduced to obtain a mechanistic understanding

Low-temperature quantum fluctuations in overdamped ratchets

At low temperatures and strong friction the time evolution of the density distribution in position follows a quantum Smoluchowski equation. Recently, also higher-order contributions of quantum fluctuations to drift and diffusion coefficients have been systematically derived. As a non-trivial situation to reveal the impact of subleading quantum corrections and to demonstrate convergence properties of the perturbation series, directed transport in ratchets is studied. It is shown that the perturbation series typically has a non-monotonous behavior. Depending on symmetry properties higher order contributions may even compensate current reversals induced by leading quantum fluctuations. This analysis demonstrates how to consistently treat the dynamics of overdamped quantum systems at low temperatures also in numerical applications.Comment: 5 pages, 3 figure

On the Way to Optoionics

Discussions with Michael Grätzel, Ursula Röthlisberger, Robert A. Evarestov and Bettina V. Lotsch are gratefully acknowledged.Based on the recent finding of significant ion conduction enhancement in iodide perovskites upon illumination, the potential of an emerging field ‘opto-ionics’ – that we define in parallelism to ‘opto-electronics’ – is explored. We emphasize that the major prerequisite is the identification of appropriate stable materials which can act as light-tunable electrolytes, permeation membranes, or electrodes. In this way, classic, but light-tunable electrochemical devices would be in reach. We also touch upon related issues such as sensing, switching, and catalysis, in which light effects on ionic charge carriers are also expected to be important.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Mixed-conducting cathode materials for protonic ceramic fuel cells: Proton uptake and defect interactions

A cathode in a proton-conducting ceramic fuel cell (PCFC) should meet several criteria including high catalytic activity, electronic conductivity, sufficient proton conductivity, phase stability, etc. to achieve good performance. The proton conductivity allows the oxygen reduction reaction to extend from the triple phase boundary to the whole surface of the cathode (so-called bulk path ). Please click Additional Files below to see the full abstract

Stoichiometry relaxation in oxides with mobile oxygen vacancies, protons and holes: Temperature dependence and trapping effects

Materials with three mobile carriers (oxygen vacancies, protons, holes) are of interest as cathode materials for proton-conducting ceramic fuel cells. The incorporation of protons into such mixed-conducting oxides can occur by acid-base hydration of oxygen vacancies as well as by hydrogen uptake.[1,2] Depending on conditions, one-fold or two-fold conductivity relaxation after pH2O steps is observed.[2-6] Exact analytical relations for these processes were derived in ref. [2]. For a complete description four diffusion coefficients are required, comprising direct as well as indirect terms. The complex non-monotonic kinetic behavior is related to the fact that in a three carrier system the electroneutrality condition does not lead to a simple coupling between the carrier fluxes. Numerical simulations for a wide range of materials and conditions are presented.[2,6] They allow us to identify the conditions for the transition from one-fold to two-fold relaxation, and give a natural explanation for the moving boundary phenomenon observed in ref. [3]. The simulations also show that the assignment of the temperature dependence of the effective diffusivities for acceptor-doped (Ba,Sr)(Zr,Ce)O3-d perovskites (large set of experimental data compiled in [7]) is far from trivial. When the transference number of oxygen vacancies exceeds that of the protons, the faster of the two effective diffusivities approaches the oxygen chemical diffusion coefficient, not the hydrogen chemical diffusivity as one might expect intuitively. Furthermore, the effect of trapping reactions on the relaxation kinetics is investigated. [1] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129 [2] D. Poetzsch, R. Merkle, J. Maier, Adv. Funct. Mater. 25 (2015) 1542 [3] J. H. Yu, J. S. Lee, J. Maier, Angew. Chem. Int.Ed. 46 (2007) 8992; Solid State Ionics 181 (2010) 154 [4] H. I. Yoo, J. Y. Yoon, J. S. Ha, C. E. Lee, Phys. Chem. Chem. Phys. 10 (2008) 974 [5] E. Kim, H. I. Yoo, Solid State Ionics 252 (2013) 132 [6] R. Merkle, R. Zohourian, J. Maier, Solid State Ionics (2016) doi:10.1016/j.ssi.2015.12.011 [7] G. R. Kim, H. H. Seo, J. M. Jo, E. C. Shin, J. H. Yu, J. S. Lee, Solid State Ionics 272 (2015) 6