Pressure-Driven Reversible Switching between n- and p-Type Conduction in Chalcopyrite CuFeS₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Temperature-dependent conduction-type switching is rare in Ag-based semiconductors.
• Pressure is an effective stimulus for inducing collective phenomena in transition metal semiconductors.

Purpose of the Study:

• To investigate pressure-driven conduction-type switching in chalcopyrite CuFeS2.
• To understand the relationship between structural, electronic, and spin properties under pressure.

Main Methods:

• High-pressure experiments using diamond anvil cells.
• X-ray diffraction for structural analysis.
• Photocurrent and Hall coefficient measurements for electronic properties.
• X-ray absorption spectroscopy (XAS) for valence state determination.

Main Results:

• CuFeS2 exhibits a reversible p- to n-type conduction switching around 8 GPa.
• A structural phase transition from space group I-42 d to I-4 occurs with FeS4 tetrahedron volume shrinkage.
• A high-to-low spin-crossover of Fe2+ (S=2 to S=0) accompanies the phase transition.
• The valence distribution remains Cu2+Fe2+S2, with no cationic charge transfer.

Conclusions:

• A novel pressure-driven p-n conduction switching phenomenon was observed in CuFeS2.
• This switching is associated with a pressure-induced structural phase transition and spin-crossover.
• CuFeS2 is a promising material for developing novel pressure-responsive electronic devices.