Exploration of Metastable A-Site-Ordered Perovskites (Ca,Ba)FeO_3-δ by Computationally Guided Multistep Synthesis

Area of Science:

• Materials Science
• Solid-State Chemistry
• Magnetism

Background:

• Perovskite-type iron oxides with Fe⁴⁺ ions exhibit versatile helimagnetic properties.
• Layered A-site ordered structures in AFeO₃ offer potential for novel helimagnetic phases.
• Synthetic pathways for these materials, especially under high pressure, are challenging to determine.

Purpose of the Study:

• To explore new A-site ordered perovskite-type iron oxides, specifically (Ca,Ba)FeO_3-δ, with Fe⁴⁺ ions.
• To investigate the thermodynamic stability of potential structures using first-principles calculations.
• To synthesize and characterize novel perovskites with potential helimagnetic properties.

Main Methods:

• First-principles calculations (DFT-based convex-hull) to evaluate thermodynamic stability.
• High-pressure synthesis to obtain oxygen-deficient perovskites.
• Low-temperature topotactic oxidation using ozone for ambient pressure synthesis.

Main Results:

• Two oxygen-deficient perovskites, CaBaFe₂O_6-δ and Ca(Ba_0.9Ca_0.1)₂Fe₃O_9-δ (δ ∼ 1), were successfully synthesized under high pressure, consistent with calculations.
• Oxidized forms, CaBaFe₂O_6-δ (δ ∼ 0.4) and Ca(Ba_0.9Ca_0.1)₂Fe₃O_9-δ (δ ∼ 0.6), were obtained via topotactic oxidation.
• These synthesized materials hold potential for exhibiting novel helimagnetic phases.

Conclusions:

• Computational visualization of high-pressure synthetic pathways accelerates the discovery of new metastable perovskites.
• The study successfully synthesized novel A-site ordered perovskites with Fe⁴⁺ ions.
• These materials offer a promising platform for exploring new helimagnetic phenomena.