Continuously tunable negative pressure for engineering high-symmetry nanocrystalline phases

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Strain engineering is crucial for tuning material properties.
• Conventional methods often rely on planar substrates, limiting strain types.
• Understanding strain effects in nanoconfined materials is essential.

Purpose of the Study:

• To demonstrate a general approach for achieving tunable, triaxial tensile strain using 3D nanoconfining scaffolds.
• To achieve and study the exotic condition of "negative pressure" in embedded materials.
• To investigate the impact of negative pressure on the structural and electronic properties of perovskite materials.

Main Methods:

• Embedding materials within 3D nanoconfining scaffolds (anodic aluminum oxide membranes).
• Utilizing thermal expansion mismatch to induce tunable, triaxial tensile strain.
• Employing controlled thermal hysteresis to tune crystal structure and octahedral rotations.

Main Results:

• Achieved continuously tunable, triaxial tensile strain and "negative pressure" (hundreds of megapascals) in CsPbI3 perovskites.
• Observed tuning of perovskite crystal symmetry toward higher symmetry with decreasing pore size (<40 nm).
• Demonstrated bandgap tunability under negative pressure, following trends of positive hydrostatic pressure and highlighting bond stretching effects.

Conclusions:

• The 3D scaffold approach provides a general method for inducing and controlling negative pressure in nanoconfined materials.
• Negative pressure significantly influences perovskite crystal structure and electronic properties, particularly bandgap and octahedral rotations.
• This work offers a framework for understanding and utilizing strain in nanocomposite materials.