Morphological and Humidity Sensing Investigations on Niobium, Neodymium, and Lanthanum Oxides

This paper reports a comparative study of moisture sensing properties of niobium penta oxide, neodymium oxide, and lanthanum oxides. Pellets of these materials were made by using hydraulic pressing machine (M.B. Instruments, New Delhi, India) at a pressure of 616 MPa. These pellets were used as sensing elements and thermally annealed at temperatures 200°C and 400°C successively. After each step of annealing, the sensing element was put within a conventionally designed conductivity holder and exposed to humidity inside a controlled humidity chamber. Variations in resistance with the relative humidity were recorded for each sensing elements made of Nb₂O₅ , Nd₂O₃ , and La₂O₃ , respectively. Sensitivities of samples were compared at different annealing temperatures. Maximum values of sensitivities and linear response of sensors were obtained for samples annealed at 400 ^°C. Lanthanum oxide revealed the highest sensitivity 20 MΩ/%RH in comparison to other samples. Morphological and X-ray diffraction studies of the samples were performed. Results were found reproducible within ±5% error. No ageing effect was observed during three months.