A Highly Selective Room Temperature NH^sub 3^ Gas Sensor based on Nanocrystalline α- Fe^sub 2^O^sub 3

Nanocrystalline a-Fe2O3 powder was synthesized by simple, inexpensive sol-gel method. The obtained powder was calcined at 700 0C in air atmosphere for 2 hours. The structural and morphological properties of calcined powder were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) respectively. Thermal properties of dried gel were studied by Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC). The XRD pattern of the powder confirmed the a-Fe2O3 (hematite) phase of iron oxide with average crystalline size of 30.87 nm calculated from Scherrer equation. The FESEM images showed uniform wormlike morphology of a-Fe^sub 2^O^sub 3^ powder. TGA result indicated that a-Fe2O3 is thermodynamically stable. Room temperature NH3 sensing characteristics of a-Fe^sub 2^O^sub 3^ were studied for various concentration levels (250-2500 ppm) of NH^sub 3^ at various humid conditions. The sensor based on a-Fe^sub 2^O^sub 3^ exhibited good selectivity and excellent sensitivity (S=92) towards 1000 ppm of NH3 with quick response of 4 sec and fast recovery of 9 sec. Room temperature sensing mechanism is also discussed.