Controlling thermal expansion and phase transitions in Ca1- xSrxMnO3- δ by Sr-content

Lena Klaas; Mathias Pein; Peter Mechnich; Alexander Francke; Dimitra Giasafaki; Dorottya Kriechbaumer; Christos Agrafiotis; Martin Roeb; Christian Sattler

doi:10.1039/d2cp04332g

Controlling thermal expansion and phase transitions in Ca_{1- x}Sr_xMnO_{3- δ} by Sr-content

Phys Chem Chem Phys. 2022 Nov 23;24(45):27976-27988. doi: 10.1039/d2cp04332g.

Authors

Lena Klaas^{1

2}, Mathias Pein^{1

2}, Peter Mechnich³, Alexander Francke³, Dimitra Giasafaki⁴, Dorottya Kriechbaumer¹, Christos Agrafiotis¹, Martin Roeb¹, Christian Sattler^{1

2}

Affiliations

¹ Deutsches Zentrum für Luft- und Raumfahrt - DLR/German Aerospace Center, Institute of Future Fuels, Linder Höhe, 51147 Cologne, Germany. Mathias.Pein@dlr.de.
² RWTH Aachen University, Faculty of Mechanical Engineering, Chair for Solar Fuel Production, 52062 Aachen, Germany.
³ Deutsches Zentrum für Luft- und Raumfahrt - DLR/German Aerospace Center, Institute of Materials Research, Linder Höhe, 51147 Cologne, Germany.
⁴ National Centre for Scientific Research "DEMOKRITOS", Institute of Nanoscience and Nanotechnology, Aghia Paraskevi, 153 41, Attica, Greece.

PMID: 36373742
DOI: 10.1039/d2cp04332g

Abstract

Perovskite oxides of the general formula ABO_3-δ, with A and B being metal cations, present themselves in various crystal structures that originate from a distorted ideal cubic perovskite. Understanding how composition, temperature, atmosphere and reduction extent of these non-stoichiometric redox materials induce structural changes on an atomic, as well as macroscopic, level is crucial to transfer newly developed materials to industrial scale applications in the redox-based energy conversion sector. Herein, Ca_1-xSr_xMnO_3-δ (x ∈ [0,0.2]) and its micro- and macroscopic structural changes at elevated temperatures and varying oxygen partial pressure are analyzed by means of in situ high temperature XRD, DSC and dilatometry. Results are expanded by room temperature XRD of compositions with higher Sr-content up to x = 0.4. By adjusting the Sr-content, the formed crystal structure can be governed and thermal expansion can be impacted beneficially in the context of future applications utilizing monolithic structures. Phase transitions from orthorhombic to cubic were found to shift from 900 °C to 830 °C under air and to even lower temperatures under 1% O₂ atmosphere. Small amounts of Sr-content (5-10%) stabilize the macroscopic structural integrity by improving the reversibility of the cyclic thermal expansion and contraction in a 1% O₂ atmosphere. However, at Sr-contents of 20% an increased irreversible residual expansion within each thermal cycle becomes apparent and shows that such improvements do not follow a linear dependency with Sr-content, but most benefits in this context can be found at Sr-contents below 20%. The results demonstrate the sensitivity of such materials micro- and macroscopic characteristics to composition. In the context of utilization of monolithic structures, fabricated entirely from Ca_1-xSr_xMnO_3-δ, in thermochemical or thermoelectric applications, the results have considerable significance as minor A-site Sr-substitution can substantially improve macroscopic stability of monolithic structures over multiple thermal cycles. Besides the often solely regarded thermodynamic characteristic, this work demonstrates the importance to consider the impact of composition on structural behavior in materials design processes including perovskites for thermochemical applications.