Strain-Induced Structural Phase Transitions in Epitaxial (001) BiCoO₃ Films: A First-Principles Study

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Materials Science

Background:

• Bismuth cobalt oxide (BiCoO3) is a multiferroic material with potential applications in advanced electronic devices.
• Understanding the interplay between strain, structure, and magnetism is crucial for tailoring its properties.

Purpose of the Study:

• To investigate the effects of epitaxial tensile strain on the structural and magnetic properties of BiCoO3 films.
• To identify low-energy phases and phase transitions under varying strain conditions.

Main Methods:

• Density functional theory (DFT) computations were employed to simulate BiCoO3 films epitaxially grown along the (001) direction.
• Analysis of magnetic ordering, structural symmetry, and ferroelectric polarization under tensile strain.

Main Results:

• Tensile strain induces a magnetic phase transition from C-type to G-type antiferromagnetic order above a lattice parameter of 3.922 Å.
• Larger tensile strains lead to continuous structural phase transitions, involving ferroelectric and antiferrodistortive modes.
• An isostructural transition (Cowley's ''Type Zero'') from Cc-(I) to Cc-(II) with a volume collapse occurs under significant tensile strain.
• Ferroelectric polarization reorients from out-of-plane to in-plane, and the magnetic ordering temperature (TN) is sensitive to misfit strain.

Conclusions:

• Epitaxial tensile strain offers a powerful route to tune the multiferroic properties of BiCoO3.
• The observed phase transitions and polarization reorientation highlight the potential for strain engineering in BiCoO3-based devices.
• DFT simulations provide critical insights into the complex strain-dependent behavior of BiCoO3 films.