Humidity sensing properties of (Ba, Sr) TiO3 thin films grown by hydrothermal–electrochemical method

Thin films of (Ba, Sr ) TiO3 ceramic have been grown on Ti electrodes in aqueous solution of (Ba, Sr) (OH)2 by hydrothermal–electrochemical method. These films are porous in nature and adsorb the water vapor when exposed to humid environment. X-ray diffraction data of as grown films shows the presence of four different peaks corresponding to barium strontium titanate. (BST) The scanning electron microscopy (SEM) shows a uniform distribution of spherical crystallites. Impedance measurements have been made at various frequencies and at different humidity levels to distinguish individual contributions to electrical conduction, arising from different sources like bulk and grain boundaries, inter granular contact regions and electrode–sample interface regions on the basis of non-Debye theory. The real part of the total complex impedance which represents the pore resistance Ri, is found to decrease by three order of magnitude with increase of humidity from 0 to 100% RH. We have proposed a physical model and its equivalent circuit to explain the skewed semicircles in the Cole–Cole plot of the experimentally acquired data.