Study of the influence of nickel ions substitutes in barium stannates used as humidity resistive sensors

In the present work, we report the results of the influence of the Ni ions which partly substitute the Ba ions in the barium stannate (Ba1−xNixSnO3, where x = 0; 0.1; 0.2; 0.5), on the structural and electronic properties, as well as on the sensitivity to humidity. With the view to obtain a porous and finer structure, thus providing a high specific surface, these materials were obtained through the precursor method of self-combustion (co-precipitation in a colloidal environment and self-combustion), followed by heat treatments. The phase composition and morphology were studied by XRD and SEM. The pure sample, as well as that with the substitution x = 0.1, are single phased after 40 min sintering at 1000 °C. For substitutions with x > 0.1 secondary phases appear, which favorably influence the humidity sensitivity. All the samples show a significant sensitivity to humidity within 22% RH and 75% RH for the substitution with x = 0 and 0.1, and 22% RH – 98% RH for the substitution with x = 0.5. For this interval, the material resistivity logarithmically decreases by over four orders. The sample with the substitution x = 0.5 is characterized by a very fine structure (∼250 nm) and a high effective porosity (47%). This sample presents a shorter absorption response time than the other samples. Its high sensitivity, its sensitivity range, linearity of the sensitivity characteristic and the quick response time recommend the material with the composition Ba0.5Ni0.5SnO3 for the realization of a very good resistive humidity sensor.

► The barium stannates doped with nickel, prepared by self-combustion method.
► The humidity sensitivity is high, and the linear segment of the sensitivity characteristic ranges between 22% and 98% RH.
► The response time is two times shorter than that of the sample without nickel substitution.