A new model and gas sensitivity of non-equilibrium xSnO₂-(1-x)α-Fe₂O₃ nanopowders prepared by mechanical alloying

Nano-sized xSnO₂-(1-X)α-Fe₂O₃ materials have been prepared using the high energy ball milling technique and their structural and gas sensing properties have been characterized. Based on experimental results, we propose a new structure model, □1/3 → Sn_1/3⁴⁺ + 2(1 - y) O_s^2- + 4yO_s^-, for these non-equilibrium, nano-sized ASnO₂-(1-x)α-Fe₂O₃ materials. This model can explain not only the lattice expansion of the milled samples, but also takes into account the charge balance by adding oxygen dangling bonds at the particle surfaces, which can be visualized in the nano-sized powders. The thick film gas sensors made by such mechanically alloyed materials have high ethanol gas sensitivity values of 289 in air and 1016 in nitrogen at 1000 p.p.m. and very good gas selectivity to ethanol over CO and H₂ gases. It is believed that the high ethanol gas sensitivity of these materials is related to the enormous defects such as O^- and O^2- dangling bonds at the particle surfaces of these nano-sized materials.