Gas-sensor properties of Re_1+xBa_2−xCu₃O_7−y

The NO and NO₂ responding properties of Nd₂CuO_4−y thick film prepared by citrating process were investigated by measuring electrical conductance in air and N₂ at 400 °C. The conductance was decreased by NO and was increased by NO₂ with quick response and recovery time, which suggests that the Nd₂CuO_4−y thick film is applicable to be a sensing element for NO and NO₂ gases. The NO_x responding properties in N₂ showed a different behavior from those in air, which suggests that NO and NO₂ responding mechanisms and their surface reactions are greatly affected by existing oxygen. Nitrate-like species were observed in N (1s) X-ray photoelectron spectra of Nd₂CuO_4−y thick film after NO_x treatment. The charges of NO_x adsorbates inferred from X-ray photoelectron spectroscopy analysis were consistent with those expected from conductance changes induced by the introductions of NO_x in air.

In this paper the theoretical and practical background of the realization of highly sensitive and selective semiconductor gas sensors is discussed. This discussion is based on the literature and some earlier published experimental results. The most important items are the quality of the semiconductor surface, the role of additives (catalytically active materials), the size of crystals or the layer thickness compared to the Debye length of the semiconductor, the quality of the interface between semiconductor crystals and the interface between the semiconductor and the grain of doping material (potential barriers). All of the listed factors depend on the technology; some of them depend on the temperature, as well as the characteristics of the realized sensor or sensor system.