Resistive λ-sensors based on ball milled Fe-doped SrTiO 3 nanopowders obtained by self-propagating high-temperature synthesis (SHS)

Abstract

A series of SrTi 1− x Fe x O 3− δ (STO or STFO) powders, with x ranging from 0 to 0.6, were prepared by self-propagating high-temperature synthesis (SHS) starting from SrO 2, Ti, TiO 2 and Fe. A ball-milling (BM) treatment was subsequently carried out for further structure refinement and size reduction. Morphological and microstructural characteristics of both untreated and ball-milled SHS samples were investigated by SEM and XRD. Screen-printed SrTi 1− x Fe x O 3− δ SHS powders on alumina substrate were investigated for resistive oxygen sensors operating at high operating temperature (450–650 °C). STFO powders have shown better performances with respect to the corresponding undoped STO ones. Moreover, when STFO powders were subjected to BM treatment, both temperature-independent resistance characteristics and sensor response greatly improved. On the basis of the reported data, it can be suggested that the ball milling treatment likely acts: (i) stabilizing the formation of non-equilibrium structures; (ii) decreasing the particle size, increasing surface defects and hence surface reactivity; (iii) favouring the substitution of titanium by iron in the SrTiO 3 perovskite structure.