Applying Configurational Complexity to the 2D Ruddlesden-Popper Crystal Structure

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Layered Ruddlesden-Popper (RP) crystal structures are known for diverse functional properties.
• Controlling cation disorder in these structures is crucial for tuning material behavior.

Purpose of the Study:

• To establish configurational disorder in a layered RP structure using entropy stabilization.
• To design and fabricate a prototype cuprate oxide with extensive A-site cation mixing.
• To investigate the influence of heteroepitaxial strain on crystal phase formation.

Main Methods:

• Pulsed laser deposition for epitaxial single crystal film fabrication.
• X-ray diffraction, atomic-resolution scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption spectroscopy for characterization.
• Systematic variation of substrate-induced strain.

Main Results:

• Achieved uniform A-site cation mixing in a (La$_{0.2}$Pr$_{0.2}$Nd$_{0.2}$Sm$_{0.2}$Eu$_{0.2}$)$_{2}$CuO$_{4}$ film with a T'-type RP structure.
• Demonstrated that compressive strain (>1.5%) induces a phase transition to a cubic CuX$_{2}$O$_{4}$ spinel structure.
• Confirmed the role of heteroepitaxial strain in dictating crystal phase formation.

Conclusions:

• Entropy stabilization enables extraordinary configurational disorder in layered RP cuprates.
• The ability to switch between 2D RP and 3D cubic phases offers a pathway for designing materials with tailored functionalities.
• This approach holds promise for applications in magnetoresistance, superconductivity, ferroelectricity, catalysis, and ion transport.