Microstructural effects on the electrical behaviour of SrTi0.95Nb0.05O3+delta materials on changing from reducing to oxidising conditions

Impedance spectroscopy has been used to investigate the electrical behaviou r of SrTi0.95Nb0.05O3+delta materials upon changing from reducing to oxidis ing conditions. Dense materials respond very slowly to these step changes i n the atmosphere. After an initial stage where the behaviour of relatively dense samples is essentially representative of an ideal resistor, the resis tance increases slowly for at least up to three weeks. However, the respons e becomes much faster for porous samples. The electrical behaviour is thus discussed in terms of porosity. The impedance and modulus responses of the densest sample revealed two microstructural components which were interpret ed in terms of a core-shell microstructure with resistive shells and conduc tive cores. Spectra obtained for a sample with intermediate density also re vealed two components at short reoxidation times. At longer times the sampl e approaches a fully reoxidised condition and the core contribution is conc ealed even in modulus representations. Very porous samples appear to be reo xidised very fast, and only show a single are in both types of representati ons (impedance and modulus plots), even at short times. (C) 2001 Elsevier S cience B.V. All rights reserved.