Extremely sensitive and selective flammable liquefied hydrocarbon gas sensing and inter-dependence of fluctuating operating temperature and resistance: Perspective of rare-earth doped cobalt nanoferrites

Abstract

In this paper, we present a variety of cobalt-based spinel ferrites doped with 4f electron rare-earth ions to be used as flammable gas sensors. These spinel ferrites were fabricated following a glycol hydrothermal chemical-process. Due to their electronic configuration and charge dynamics, they are very sensitive and selective to integrative liquefied petroleum gases (LPG). A high response of over 730 was recorded towards 1 vol% of LPG at 225 °C. The CoSm0.1Fe1.9O4 nano-ferrite meets the criteria of a potential sensor of being highly sensitive and selective with repeatability and stability that maintained a high response of 241 over 63 days. The rare-earths doped cobalt based ferrites were classified according to two categories in terms of overall performance. The first category were the ferrites doped with the low 4f electrons and the second category belonged to the high 4f electrons. The first category composed of solid and compact nanoparticles and proved to be better in the LPG performance while giving a low photoluminescence emission intensity. This latter category had the highest combined percentages of oxygen vacancies and adsorbed oxygen. A temperature dependent tuneable carrier-type transition was observed. The ferrite has p-type characteristics at 225 °C and above, otherwise n-type below this operating temperature to room temperature.