ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Effect of oxygen diffusion path radii on the oxygen intake/release properties of Brownmillerite SrCoO( _{2.5} )

Aswathy M. Narayanan and Arun M. Umarji

Materials Research Centre, Indian Institute of Science, Bengaluru, India

E-mail: aswathyn@iisc.ac.in

Received: 14 October 2020  Accepted: 1 February 2021

Abstract:

Abstract

Chemical modification has been proved to be an effective way to tune various material properties. Herein, the oxygen intake/release properties of substituted Sr( _{1-x} )M( _{x} )CoO( _{2.5} ) (M = Ca, Ba, x = 0.02 (2 at. %), 0.05 (5 at. %), 0.1 (10 at. %), and 0.2 (20 at. %)) are explored. The substitution range was limited to the stability range of the brownmillerite structure. Phase purity and the unit cell expansion/contraction by substitution were confirmed by X-ray diffraction. The oxygen intake/release of the substituted samples was characterized by a custom-built volumetric apparatus and iodometric titration. Thermal expansion coefficient and electrical conductivity measurements were carried out on substituted samples. The reversible oxygen intake/release was found to decrease with both Ba and Ca substitution, even though a reduction in activation energy by Ba substitution was observed. This is correlated with an increased bond dissociation energy and a drastic decrease in critical radius of the bottle neck through which oxide ion migration occurs, especially with Ba substitution.

Graphic abstract

Keywords: Perovskite oxide; Brownmillerite; Oxygen non-stoichiometry; Mixed ion electron conductor

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-021-01555-5

Chemical Papers 75 (7) 3241–3251 (2021)