Lanthanum doped barium stannate for humidity sensor

A few samples in the system Ba1-xLaxSnO3 (x = 0.00, 0.01, 0.05 and 0.10) have been synthesized by the solid state ceramic route. Powder X-ray diffraction (XRD) pattern of the samples was recorded to confirm the formation of a single phase solid solution. The inferences drawn from the analysis of the X-ray diffraction pattern are that, the lattice parameter and bulk density decrease with increasing concentration of lanthanum. The resistance and capacitance of all the samples in the frequency range 20 Hz-1 MHz and relative humidity (RH) range 10-95% have been measured at 31 degrees C. It is observed that the frequency has more influence on the capacitance as compared to resistance. Among all the samples, the sample Ba0.99La0.01SnO3 (bearing sample code BSL1) exhibits superior response to the change in humidity. The resistance of sample BSL1 changes almost three orders of magnitude where as capacitance changes only one order of magnitude within the RH range 10-95%. The variation of conductivity with RH for samples BSL0 and BSL1 is linear. The response and recovery time of these samples during adsorption and desorption of water vapor are less than 1 min. It is observed that at a particular relative humidity, temperature and frequency (i.e. for RH 10%, temperature 31 degrees C and frequency 1 kHz) conductivity of barium stannate increases sharply (almost four orders of magnitude) as dopant (La) concentration increases from 0 to 10 mol% which is explained in terms of charge compensation mechanism. (c) 2006 Elsevier B.V. All rights reserved.