Defect chemistry modelling of oxygen-stoichiometry, vacancy concentrations, and conductivity of (La1-xSrx)(y)MnO3 +/-delta

Two precise algorithms are devised for the calculation of defect concentrat ions in A-site acceptor doped ABO(3) perovskites. The two models contain ni ne species including cation vacancies on the A- and B-site. The small polar on model is based on three redox levels of the B-ion. A large polaron model , based on delocalised electrons, electron holes and all B-ions being triva lent is given in Appendix A. The sequential mathematical method allows us t o calculate the high temperature oxygen partial pressure dependent properti es of (La1-xSrx)(y)MnO3+/-delta in a unified manner irrespective of the typ e of defect regime, Simulations are shown for a pO(2) span from 10(-30) to 10(5) atm. The three required equilibrium constants for (La1-xSrx)(y)MnO3+/ -delta had to be changed significantly from values given in literature in o rder to match the observed stoichiometry span. The main results shown are c alculated by the small polaron model containing only ionic species - the B- ion may be Mn-B' (Mn2+), Mn-B(x) (Mn3+), and Mn-B(Mn4+). The A/B-ratio = y greatly influences the oxygen stoichiometry, oxygen ion vacancy- and cation vacancy concentrations and the total conductivity. Calculations are given for the range 0.87 less than or equal to y less than or equal to 1.13 for a Sr doping of 10% at 1000 degrees C. The defect model can simultaneously de scribe the observed stoichiometry and conductivity dependence on pO(2), if the electronic mobility is decreased by up to 50% at pO(2) < 10(-10) and pO (2) > 10(-2) arm. (C) 2000 Elsevier Science B.V. All rights reserved.