Barium perovskites as humidity sensing materials

The response to humidity of porous ceramics with composition BaMO3, with M = Ti, Zr, Hf or Sn, was studied. Samples were obtained by cold isostatic pressing and sintering of fine powders prepared by wet chemical synthesis. Sensitivity and response time have been obtained by electrical impedance measurements realised in different conditions of relative humidity (R.H.) at 25°C. An increase of both capacitance and conductivity with humidity was observed in all samples with open porosity. Sensitivity increased with R.H. and decreased with frequency, indicating a major contribution from the surface of crystals exposed to water vapour, particularly in BaTiO3 where 4000% change in permittivity was registered over the range 20-80% R.H. Time response was in the typical range of capacitive humidity sensors, with fast (10-100 s) equilibration time for intermediate values of R.H.