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The La2LiNbO6 perovskite has been prepared in the polycrystalline form by a solid state reaction. Structural characterization by means of monochromatic X-ray and neutron powder diffraction (XRD and ND) and Rietveld refinement showed that the crystal structure belongs to the group of 1 : 1 B-site rock-salt ordered double perovskites with the most common tilting system amongst them being a-a-b+ (S. G. P21/n, a = 5.61612(3), b = 5.76645(2), c = 7.94107(4) degrees A, b = 90.276(2)degrees). Scanning Transmission Electron Microscopy (STEM) evidences that there is no cross-substitution between Li and Nb and that a remaining portion of lanthanum is randomly located in the projected positions of lithium. Impedance spectroscopy has been used to analyse the electrical-response properties of the materials. Conductivity is strongly dependent on the relative humidity (RH), changing by about 3 orders of magnitude between 25 and 90% RH. However, no conductivity increase with change in RH% is observed when the lateral surfaces of the sensor are covered with paraffin. This confirms that adsorption of water by the sample plays a crucial role in modulating the conduction mechanism. La2LiNbO6 also exhibits a very good durability, reproducibility, response time, hysteresis and dynamic linearity to be considered as a promising sensing material for a practical humidity sensor. ; This work has been supported by Projects funded by the regional government (Comunidad de Madrid through MATERYENER3CM S2013/MIT-2753) and the Spanish Government, (MICINN through MAT2016-78362-C4-3R and MAT2016-78362-C4-4R). V.D.N. thanks the University Carlos III of Madrid for the "8220;Cátedras de Excelencia UC3M-Santander"; (Chair of Excellence UC3M-Santander).

This article also appears in: In Memoriam: Prof. Jean-Michel Savéant. ; In this report, the conductivity mechanism of Ca2+-ion in polyoxyethylene (POE) solid polymer electrolytes (SPEs) for calcium secondary batteries is investigated by broadband electrical spectroscopy studies. SPEs are obtained by dissolving into the POE hosting matrix three different calcium salts: CaTf2, Ca(TFSI)2 and CaI2. The investigation of the electric response of the synthetized SPEs reveals the presence in materials of two polarization phenomena and two dielectric relaxation events. It is demonstrated that the nature of the anion (i. e., steric hindrance, charge density and ability to act as coordination ligand) and the density of "dynamic crosslinks" of SPEs is fundamental in the establishment of ion-ion/ion-polymer interactions. The long-range charge migration processes occurring along the two revealed percolation pathways of the electrolytes are generally coupled with the polymer host dynamics and depend on the temperature and the anion nature. This study offers the needed tools for understanding Ca2+ conduction in POE-based electrolytes. ; This work has been supported by the European Union's Horizon 2020 research and innovation programme under grant agreement No 829145(FETOPEN-VIDICAT).V. Di Notothanks the University CarlosIII of Madrid for the "Catedras de Excelencia UC3M-Santander" (Chairof Excellence UC3M-Santander).