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