Resistive Modeling of a Novel K₂CO₃/Al₂O₃ Nanostructure as a Solid Electrolyte NO₂ Sensor

The electrical resistance of a solid electrolyte sensor with an ionic conductor is theoretically modeled. The results of applying the proposed model to the K2CO3/Al2O3 composite pellet in clean air and in the presence of NO2 is reported. The XRD pattern and FESEM images of the synthesized samples suggested the formation of a nanosized KAl(CO3)2(OH)2 structure around an alumina core. Accordingly, this sample was considered based on the brick-wall model in which each grain consisted of alumina as the bulk and K• ion as the mobile ion in the grain-boundary layer. Some equations were found for the dependence of the electrical resistance along with the capacitance of the sample on nanostructural parameters such as grain size, grain-boundary width, and, consequently, Schottky barrier height. The stimulation of the sample with voltage pulses at temperatures close to room temperature, i.e., 10–45 °C, and calculating the nanostructural parameters appearing in the model indicated that the Schottky barrier height and grain-boundary width in the presence of NO2 changed with temperature through a power function, whereas both parameters were temperature independent in clean air. The sharp decrease in the Schottky barrier height in the presence of NO2 relative to clean air, especially at low temperatures, suggested that this novel nanostructure could act as a p-type NO2 sensor at room temperature and lower temperatures. This sensor can detect 40 ppb NO2 with a static response of 2.2 and good selectivity to alcohol vapors.