Study of the humidity-sensing mechanism of CaCu3Ti4O12

CaCu3Ti4O12 (CCTO1) is observed to respond to water vapor by changing its capacitance. To investigate the underlying reason for the humidity-sensitive properties of CCTO, impedance spectroscopy and electric modulus plot measurements were performed at different relative humidities (RH2). Additionally, DC bias was applied to the measurement. The results indicate that the adsorption of water molecules affects the potential barrier capacitances at the CCTO/electrode interface and at the grain boundary, which further changes the total capacitance of CCTO. In addition, new low-frequency polarization relaxations were observed at high RH. The new polarization relaxations may be related to the orientation polarization and space charge polarization caused by the physically adsorbed water molecules. The two polarizations may account for the large increase of capacitance at high RH.