Composition-tuned lithium aluminosilicate as a new humidity-sensing ceramic material with high sensitivity

Though numerous types of humidity sensors have been proposed to date, the continuous emergence of new applications requires relentless improvements in sensor performance and a constant pursuit of new sensing materials. Herein, the composition of lithium aluminosilicates (LiAlSi2O6 and Li2Al2SiO6) that slightly absorb H2O molecules is tuned along with the addition of LiCl and Si2N3, in order to maximize the H2O adsorption. The optimal composition is discovered via use of a particle swarm optimization algorithm, which is a population-based metaheuristic approach. After three generations of searching, we finally develop Li2.10Al1.23Si1.54Cl0.05O5.95 (LAS-CNO), which shows the highest value of RRH=43 %/RRH=75 % (R is ionic resistance and RH is the relative humidity). Density-functional-theory calculation also reveals that the presence of Cl− and a vacancy defect on Al/Si sites contribute to preferential H2O adsorption on the (001) surface of LAS-CNO (hexagonal P6222). Accordingly, the magnitude of impedance (│Z│) at 100 Hz significantly varies from 200 MΩ (RH = ca. 0 %) to 1.0 kΩ (RH = 97 %), in contrast to relatively small decreases in │Z│ to 630 and 59 kΩ for LiAlSi2O6 and Li2Al2SiO6, respectively. An almost linear of │Z│ vs. RHs is also observed for RH values ranging between 9 and 97 %. Furthermore, the linearity is not weakened and the values of │Z│ are not significantly altered with measuring-frequencies. Due to strong H2O adsorption on LAS-CNO, hysteresis is noticeable between the adsorption and desorption processes, but other superior properties (sensitivity, stability, and linearity) validate that LAS-CNO could be a new humidity-sensing material.