Characteristic Analysis Of Humidity Sensors Based On KNN/mesoporous BLT Perovskite Materials

As acquisition unit of humidity information, the humidity sensors have been used in every field of human production and living, such as environmental monitoring, military defense,industrial, warehouse storage and weather, which is a very important member of the sensor family, and the humidity sensors have gained considerable attention. In our work,K0.5Na0.5NbO3(KNN), Bi3.25La0.75Ti3O12(BLT), mesoporous BLT and mesoporous BLT nanorods are synthesized via metal organic decomposition method(MOD), nanocasting and electrospinning method. The humidity sensors are fabricated and their humidity sensing performances and mechanism are analyzed and studied. The main results are summarized as follows.1. KNN powder is synthesized by MOD, and characterized by XRD, SEM and EDS. The humidity sensing properties of KNN powder is investigated at different relative humidity(RH)by using the CHS-1 intelligent humidity sensitive analysis system and humidity generation sources. By using the complex impedance plots, we discuss the humidity sensing mechanism based on the KNN powder humidity sensor. The results show:(a) The crystalline structure of KNN powder is perovskite structure, and the morphology of KNN powder is of cuboid microstructure with diameters of 2-5 um.(b) The variations of the KNN humidity sensor impedance are about four orders of magnitude within the whole humidity range from 11% to95% relative humidity(RH) at the frequencies of 60 Hz and 100 Hz.(c) The response time and recovery time of the KNN humidity sensor are about 8 sand 18 s, and their maximum hystereses are around 2% RH at 60 Hz and 100 Hz.(d) We can found that the humidity sensing improvement can be explained by the high solubility of Na+ and K+ ions combining with its good conductivity in water.2. BLT powder is synthesized by MOD and mesoporous structure is formed in the BLT powder via nanocasting method. Then, XRD, SEM and TEM are used to characterize the morphology and crystalline structure of BLT and mesoporous BLT powders. The humidity sensing properties of BLT and mesoporous BLT powders are investigated at different relative humidity(RH) by using intelligent humidity sensitive analysis system and humidity generation sources. By using the complex impedance plots, we discuss the humidity sensing mechanism based on the mesoporous BLT powder humidity sensor. The results show:(a) The crystalline structure of BLT and mesoporous BLT powders is both perovskite structure.Mesoporous BLT powder is of fluffy microstructure and is featured by a high porosity. The BET surface area and pore volume of mesoporous BLT powder(10.8 m2/g) are remarkably higher than those of BLT powder(0.4 m2/g).(b) The optimum working frequency of BLT andmesoporous BLT humidity sensors are both 100 Hz, and the impedance variation of M-BLT humidity sensor is about six orders of magnitude within the whole humidity range from 11%to 95% RH, which is six times more than it of BLT humidity sensor(only about one order of magnitude).(c) At the frequency of 100 Hz, the response and recovery time of mesoporous BLT humidity sensor are 32 s and 68 s, and the maximum hysteresis is around 12% RH at the range 11-95% RH.(d) By comparison, mesoporous structure is beneficial for enhancing the humidity sensing properties of materials. By analyzing the relationship between the material special morphology and humidity sensing properties, we summarize humidity mechanism of the mesoporous BLT humidity sensor.3. The mesoporous BLT nanorods are synthesized by electrospinning technique combining with nanocasting method. The crystal structures, morphologies and compositions of mesoporous BLT nanorods are characterized by XRD, SEM, TEM and EDS, and the humidity sensing properties of mesoporous BLT nanorods are investigated at different relative humidity(RH). Based on investigation for the complex impedance plots and the morphologies of mesoporous BLT nanorods, the humidity sensing mechanism based on the mesoporous BLT nanorods humidity sensor is discussed. The results show:(a) The crystalline structure of mesoporous BLT nanorods is orthorhombic phase, and the morphologies of mesoporous BLT nanorods are of rod-like microstructures.(b) The best working frequency of M-BLT nanorods humidity sensor is 100 Hz, and the impedance changes more than six orders of magnitude within the whole humidity range from 11% to 95% RH.(c) The response time and recovery time of the mesoporous BLT nanorods humidity sensor are about 8 s and 250 s, and the maximum hysteresis is about 4% RH.(e) The mesoporous BLT nanorods are of mesoporous structure and nanorods structure which increase the adsorption of water molecule.