High-pressure polymorphism of BaFe₂Se₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity Research

Background:

• Barium iron selenide (BaFe2Se3) is a material of interest for its potential superconducting properties.
• Previous studies indicated a superconducting transition temperature (Tc) of 11 K at ambient pressure.
• The presence of potential iron selenide (FeSe) impurities, which also superconduct, necessitates distinguishing the origin of superconductivity in BaFe2Se3.

Purpose of the Study:

• To investigate the intrinsic superconductivity of BaFe2Se3 under high pressure.
• To differentiate between superconductivity originating from BaFe2Se3 and potential FeSe impurities.
• To characterize the structural transformations of BaFe2Se3 under applied pressure.

Main Methods:

• Electrical resistivity measurements up to 20 GPa.
• Single-crystal and powder X-ray diffraction (XRD) studies up to 51 GPa.
• Analysis of superconducting transition temperature (Tc) as a function of pressure.

Main Results:

• Superconductivity persists around 10 K at 5 GPa, supporting intrinsic superconductivity in BaFe2Se3.
• The superconducting signal is suppressed at higher pressures, with the material becoming insulating above 20 GPa.
• Two structural phase transitions were observed: a second-order transition above 3.5 GPa (Pnma to Cmcm) and a first-order transition at 16.6 GPa (γ-BaFe2Se3 to δ-BaFe2Se3).

Conclusions:

• The superconductivity observed in BaFe2Se3 is intrinsic to the material, not due to FeSe impurities.
• BaFe2Se3 undergoes significant structural changes under pressure, including transitions to Cmcm and a distinct δ-phase.
• High pressure leads to the suppression of superconductivity and the emergence of an insulating state in BaFe2Se3.