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) Å, β = 90.276(2)°). 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.