Synthesis, characterization and humidity sensing properties of Sr(II)-added BaAl2O4 composites

Strontium(II)-added BaAl2O4 composites prepared by sol–gel technique was investigated for humidity sensing properties. X-Ray diffraction, scanning electron microscopy (SEM), FT-IR spectroscopy and nitrogen adsorption/desorption isotherms at 77 K were employed to identify the structural phases, surface morphology, vibrational stretching frequencies and BET surface area of the composites, respectively. The composites were prepared with the addition of Sr(II) of different molar ratios (0, 0.2, 0.4, 0.6, 0.8 and 1.0) to BaAl2O4 and were labeled as BaSA1, BaSA2, BaSA3, BaSA4, BaSA5 and BaSA6, respectively. The samples sintered at 900 °C for 5 h were subjected to dc resistance measurements as a function of relative humidity (RH) in the range 5–98% and the results revealed that the sensitivity factor (Sf = R5%/R98% were the dc resistances at 5% and 98% RH) increased with an increase in strontium molar ratio. Among the different composites prepared, BaSA5 possessed the highest humidity sensitivity of Sf = 39,000, while the pure composite BaSA1 possessed a low sensitivity of Sf = 8700. The response and recovery characteristics of the maximum sensitivity sample BaSA5 were 120 and 50 s.