Realizing Persistent Zero Area Compressibility over a Wide Pressure Range in Cu₂ GeO₄ by Microscopic...

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Zero area compressibility (ZAC) is a rare mechanical property where a material's 2D size remains constant under hydrostatic pressure.
• Existing ZAC materials are typically constructed as 2D units.
• A new strategy is needed to explore ZAC in different material architectures.

Purpose of the Study:

• To propose and demonstrate a new method for achieving ZAC by microscopically braiding 1D zero compressibility units.
• To identify and characterize ZAC in a novel copper-based compound, Cu2GeO4.
• To elucidate the underlying mechanism responsible for the ZAC behavior in Cu2GeO4.

Main Methods:

• Theoretical proposal of orthogonal braiding of 1D zero compressibility strips.
• Synthesis and high-pressure structural analysis of Cu2GeO4 using X-ray diffraction.
• High-pressure Raman spectroscopy.
• First-principles electronic structure calculations.

Main Results:

• Zero area compressibility (ZAC) was identified in Cu2GeO4, exhibiting an area compressibility of 1.58(26) TPa⁻¹ over a wide pressure range (0–21.22 GPa).
• The ZAC behavior arises from a balance between the shrinkage of planar [CuO4] units and the expansion of the [CuO4]-[CuO4] dihedral angle.
• Under pressure, electron transfer from d(x^2-y^2) to d(z^2) orbitals in copper atoms drives the counterintuitive expansion of the dihedral angle.

Conclusions:

• A novel strategy of braiding 1D zero compressibility units successfully yields ZAC behavior in a 3D material.
• Cu2GeO4 exhibits ZAC due to unique electronic and structural responses under pressure.
• This work offers insights into pressure-induced structural evolution in copper oxides and opens new avenues for designing anomalous mechanical materials.