Compression mechanism of HoBaCo4O7, a compound with oxygen absorption/desorption capabilities

Abstract

Recently, a new family of isostructural cobaltates (MBaCo4O7, M = In, Y, Ln) has been synthesized [1]. These cobaltates belong to a new class of geometrically frustrated magnets which not only exhibit interesting magnetic-, electronic-, thermoelectric- and electrochemical-properties; but they also have a remarkable low-temperature oxygen absorption/desorption capability which makes them suitable as oxygen sensors, oxygen permeation membranes and solid oxide fuel cells (SOFCs) [2-3]. For example, YBaCo4O7+δ reversibly absorb and desorb oxygen up to δ ≈ 1.5 in a narrow temperature range, 470-673 K [2]. Hence, an amount of oxygen that corresponds to ~20% of the total oxygen content is readily loaded or removed being triggered by just a tiny change in temperature or atmosphere. This oxygen capability substantially exceeds in the overall magnitude and in the response sensitivity to those achieved with, for example, SrFeO3 (perovskite structure) and YBa2Cu3O7 (perovskite-like structure) [3]. It is well known that the oxygen diffusion properties of perovskite-like compounds are affected not only by the temperature and surrounding oxygen partial pressure but also by their crystal structures. Therefore, a different crystal structure will result in different oxygen diffusion properties. There is currently a discussion about whether the MBaCo4O7 crystallizes in the space group P63mc or in the trigonal subgroup P31c at room temperature; or whether MBaCo4O7 undergoes temperature-induced structural phase transitions at low temperature or not. Nothing is known about the influence of pressure on MBaCo4O7 compounds, but the apparent thermal instability suggests that these compounds will undergo structural phase transitions at elevated pressure. © 2021 HASYLAB