Browsing by Author "Friedrich, A"

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    Compression mechanism of HoBaCo4O7, a compound with oxygen absorption/desorption capabilities
    (Deutsches Elektronen-Synchrotron, 2007) Juarez-Arellano, EA; Avdeev, M; Macquart, RB; Friedrich, A; Morgenroth, W; Wiehl, L; Winkler, B
    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
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    High-pressure behavior and equations of state of the cobaltates YBaCo4O7, YBaCo4O7+δ, YBaCoZn3O7 and BaCoO3−x
    (Elsevier, 2012-12-01) Juarez-Arellano, EA; Avdeev, M; Yakovlev, S; Lopez-de-la-Torre, L; Bayarjargal, L; Winkler, B; Friedrich, A; Kharton, VV
    The compressibilities of the cobaltates YBaCo4O7, YBaCo4O7+δ, YBaCoZn3O7 and BaCoO3−x were investigated by in situ powder X-ray diffraction experiments up to 30GPa using diamond anvil cells. Pressure-induced phase transitions and amorphization were observed in all the samples. The onset of the pressure-induced phase transition and the onset of the amorphization were observed at ∼11.7 and 12.2GPa (YBaCo4O7), at ∼14.2 and 16.1GPa (YBaCo4O7+δ), and at ∼16.7 and 18.7GPa (YBaCoZn3O7), respectively. An attempt to laser anneal at high-pressure failed as it led to a decomposition of the YBaCo4O7 phase into a mixture of phases. Fits of second- and third-order Birch–Murnaghan equations-of-state to the p–V data result in B0=109(3)GPa for YBaCo4O7; B0=186(4)GPa and B′=1.5 for YBaCo4O7+δ; and B0=117(1)GPa for YBaCoZn3O7. The high-pressure behavior of the studied compounds was compared with isostructural compounds and it is shown that the oxygen-content has a very large effect on the high-pressure behavior of this class of materials. © 2012 Elsevier Inc.
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    Observation of a ferroelastic phase transition in the YBaCo4-xZnxO7+δ system
    (DFG, 2009) Juarez-Arellano, EA; Avdeev, M; Lopez-de-la-Torre, L; Yakovlev, S; Bayarjargal, L; Winkler, B; Friedrich, A
    No abstract available
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    Single-crystal structure of HoBaCo4O7 at ambient conditions, at low temperature, and at high pressure
    (American Physical Society, 2009-02-18) Juarez-Arellano, EA; Friedrich, A; Wilson, DJ; Wiehl, L; Morgenroth, W; Winkler, B; Avdeev, M; Macquart, RB; Ling, CD
    We show that the correct space group of HoBaCo4O7 at ambient conditions is P63mc and that no temperature-induced or pressure-induced structural phase transition occurs down to 100 K or up to 9 GPa. The ompressibility of HoBaCo4O7 is mainly determined by a combination of bond compression and changes in the three-membered and six-membered rings of the kagomé layers. HoBaCo4O7 is more compressible than structurally related compounds due to the comparatively compressible Co-O bonds. The structural analysis allows us to propose an atomistic model for the extremely high oxygen incorporation capability of HoBaCo4O7. ©2009 American Physical Society