Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+δ Thin Films

Abstract

Reduction of the operating temperature to an intermediate temperature range between 350 °C and 600 °C is a necessity for Solid Oxide Fuel/Electrolysis Cells (SOFC/SOECs). In this respect the application of proton-conducting oxides has become a broad area of research. Materials that can conduct protons and electrons at the same time, to be used as electrode catalysts on the air electrode, are especially rare. In this article we report on the proton conduction in expitaxially grown BaFeO2.5+δ (BFO) thin films deposited by pulsed laser deposition on Nb:SrTiO3 substrates. By using Electrochemical Impedance Spectroscopy (EIS) measurements under different wet and dry atmospheres, the bulk proton conductivity of BFO (between 200 °C and 300 °C) could be estimated for the first time (3.6 × 10−6 S cm−1 at 300 °C). The influence of oxidizing measurement atmosphere and hydration revealed a strong dependence of the conductivity, most notably at temperatures above 300 °C, which is in good agreement with the hydration behavior of BaFeO2.5 reported previously.

Synthesis and characterisation of fluorinated epitaxial films of BaFeO2F: tailoring magnetic anisotropyviaa lowering of tetragonal distortion

“…In agreement with our previous ndings, 29,30 the XRD measurements showed that the BFO lm can be grown in a pseudo-cubic phase (see black curves in Fig. 3a Aer uorination, the BFOF lms do not show any signicant change in orientation or strong relaxations within the lm, as no additional reections are observed in the XRD patterns.…”

“…(1) The spectrum observed for BFO is similar to our previous study of 200 nm thick lms. 29 It can be tted with a similar distribution of sextets as reported for bulk BaFeO 2.5 (ref. 23) (see Table 2 and Fig.…”

“…The t shows that although no long-range ordering of anion vacancies can be obtained within a strained lm, the overall distribution of coordination polyhedra must be considered to be similar to the bulk state. 29 (2) On uorination of the lm to BFOF, the complexity of the spectrum strongly reduces. The spectrum can then be basically tted with one sextet and one doublet (see Table 3 and Fig.…”

“…Here, we report two different approaches to topochemical uorination of epitaxially grown BFO thin lms on single crystalline (001) oriented substrates of SrTiO 3 . 29,30 We show that the lms can be chemically uorinated via different approaches under formation of BFOF without signicant substrate uorination. Via a combination of structural analysis, Mössbauer spectroscopy as well as magnetic studies, an improved understanding of the structural and magnetic behaviour of the lms could be gained.…”

Preparation of Hydrogen Electrodes of Solid Oxide Cells by Infiltration: Effects of the Preparation Procedure on the Resulting Microstructure

“…Fuel cells, in particular solid oxide fuel cells (SOFCs), fulfill these needs [1,2]. SOFCs convert chemical energy into electricity when working at high temperature, usually 700-1000 • C. However, this temperature should be reduced [3]. In assembly, the fuel cell should work for a very long time without the need to replace components [4].…”