Electrical and humidity sensing properties of tin(IV) oxide-tin(II) molybdate composites

Experimental results on composites made from SnMoO4 (SM) and SnO2 (SO) as candidate materials for humidity sensing are described. Sintered polycrystalline disks of SnMoO4 (SMSO-10), SnO2 (SMSO-01) and composites of SM and SO in the mole ratios 8:2, 6:4, 4:6 and 2:8 designated as SMSO-82, 64, 46 and 28 respectively and doped with 2 mol % of LiOH·H2O were subjected to d.c. conductance measurements over the temperature range 100–400 °C in inert atmosphere from which activation energies were determined. The thermoelectric power measurements in the temperature range 250–400 °C in ambient air revealed the materials to be n-type semiconductors. The average value of coefficient of TEP at 400 °C is compared. Since n-type materials are preferred for humidity sensing, the terminal phases and the composites were subjected to d.c. resistance measurements as a function of relative humidity in the range of 5–98% RH, achieved by different water vapor buffers thermostated at 25 °C. The sensitivity factor, Sf (R5%/R98%) measured at 25 °C revealed that SMSO-46 has the highest humidity sensitivity, greater than 103. The response and recovery characteristics of SMSO-46 were assessed.