On the Hebb-Wagner polarisation of SrTiO3 doped with redox-active ions

Hebb-Wagner polarisation is analysed for the case that internal redox-reactions complicate the situation. In the general case current-voltage characteristics deviate significantly from the Hebb-Wagner equation. Analytical results are derived and relevant approximations given. Theoretical and experimental current-voltage relations obtained for a 2.15 x 10(18) cm(-3) Fe-doped SrTiO3 single crystal at Po-2 = 10(5) pa, agree reasonably well, and the results of the partial conductivities match findings obtained from other experiments. In addition, the fact is emphasised that a Hebb-Wagner-type current-voltage relation only requires the fulfilment of a power law for the non-blocked carrier concentrations with respect to the component partial pressure and not a field-free situation. In this case the Faraday constant appearing in the Hebb-Wagner equation has to be replaced by alpha F, where alpha is the product of the number of electrons necessary to ionise the gaseous component (n) times the absolute characteristic exponent (\N\). The condition of zero field, i.e. negligible chemical potential gradient with respect to the non-blocked species is identical to \N\ = 1/n. If \N\ = const not equal 1/n, the internal field is non-zero but is still proportional to the gradient of the component potential. (C) 2000 Elsevier Science B.V. All rights reserved.