Interplay between humidity, temperature and electrical response of a conductivity sensor based on a La2LiNbO6 double perovskite

Abstract

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).