Oxygen Non-Stoichiometry and Electrical Conductivity of La_0.2Sr_0.8Fe_0.8B_0.2O_{3 − δ}, B = Fe, Ti, Ta

Abstract

The oxygen non-stoichiometry was determined by coulometric titration for the perovskite oxides La 0.2 Sr 0.8 FeO 3−δ and La 0.2 Sr 0.8 Fe 0.8 B 0.2 O 3−δ (B = Al 3+ , Ti 4+ and Ta 5+ ) in the temperature range 600• C and the oxygen partial pressure range: 1 · 10 −15 ≤ p O 2 ≤ 0.209 atm. The non-stoichiometry (δ) is observed to decrease with B-site substitution of Fe. The data can be well fitted with simple defect chemistry models. At low oxygen non-stoichiometry all compositions show a deviation from a localized electrons defect model. The standard and partial molar thermodynamic quantities were obtained and a gradual transition from localized to itinerant electrons with decreasing non-stoichiometry is proposed from the δ-dependency of the configurational entropy. The absolute value of the enthalpy of oxidation decreases upon B-site substitution of Fe proposing a decreased thermodynamic stability for the substituted materials. The electrical conductivity was measured at T = 900• C in the oxygen partial pressure range: 1 · 10 −17 ≤ p O 2 ≤ 0.209 atm. The electrical conductivity and charge carrier mobility decrease upon 20% substitution of Fe roughly by a factor of 2, but do not show a significant dependence on the nature of the B-site dopant.

Determination of oxygen nonstoichiometry in SrFeO3−δ by solid‐state Coulometric titration

“…Values of K O determined at the perovskite phase region ( p O 2 =0.32 atm) are plotted against reciprocal temperature in Figure B. The previous results for SrFeO 3−δ (SF_Merkulov), La 0.5 Sr 0.5 FeO 3−δ (L5S5F_Mizusaki) and La 0.2 Sr 0.8 FeO 3−δ (L2S8F_Lohne) are also shown for comparison . The values at oxidizing conditions are comparable with those for the same composition (SF_Merkulov).…”

Oxygen permeation in symmetric and asymmetric La0.2Sr0.8Fe0.8Ta0.2O3−δ membranes

“…In our case LSFTa composition has Vm=36.24 cm 3 /mol and it is proved to be constant within current experimental conditions [10]. The variation in cv with respect to pO2 is based on data given by Lohne et al [18] and is, for simplicity, converted to a 2 nd degree polynomial, taking into account that at 900 o C and 10 -16…”

“…The trend lines were used to establish the ratio between the oxygen fluxes for asymmetric LSFTa membranes with different surface finish, and are summarized in Table 1. Oxygen flux rates as high as 8.8 NmL min -1 cm -2 were obtained for both macro-and micro-structured asymmetric membranes at 1000 C. Based on available nonstoichiometry data for LSFTa composition [18] and using Eq. 4, one can estimate the variation in flux (jO2) in terms of log pO2 at a given temperature.…”

Oxygen Exchange and Transport in (La0.6Sr0.4)0.98FeO3-d– Ce0.9Gd0.1O1.95Dual-Phase Composites

“…The analysis of data of the oxygen transport properties for pO 2 < 0.01 atm was done by taking gas concentration polarization into consideration, due to the uptake/release of oxygen from the sample. 51 Fitting parameters.-ECR is a well-established method to determine the oxygen transport properties of MIECs. 10,11 ECR measures a change of the conductivity of a sample being subjected to a step change in the surrounding pO 2 .…”