Humidity sensitive properties of K+-doped SnO2–LiZnVO4

The humidity sensitive properties of pure and K+-doped SnO2–LiZnVO4 sensors were studied. The electrical resistance changes of the samples doped with different K+ concentrations were investigated at different relative humidity (RH) levels. It was found that pure SnO2–LiZnVO4 showed sensitivity only in the RH above 55%. The addition of K+ ion was beneficial for improving the humidity sensitive properties of the sample. The best results were obtained with the 2.5-mol% K+-doped sample, which exhibited excellent linearity in the humidity range of 33–93%. A resistance variation of about four orders of magnitude, better resistance–RH linearity, a narrow hysteresis loop, and rapid response were obtained. The impedance measurements at different operation frequencies indicated that the 2.5-mol% K+-doped sensor had the optimum resistance–RH linearity at 100 Hz to 10 kHz. Scanning electron microscopy images of the grain structures were associated with a fine microstructure morphology, which was characterized by suitable rod-shaped grains forming mesopores and by well-distributed LiZnVO4 additives, forming a thin glassy surface covering.