Colossal Negative Area Compressibility in the Ferroelastic Framework Cu(tcm)

Area of Science:

• Materials Science
• Crystallography
• Mechanics of Materials

Background:

• Copper(I) tricyanomethanide (Cu(tcm)) is a flexible framework material.
• Negative Area Compressibility (NAC) is a rare phenomenon with potential applications in sensors and actuators.

Purpose of the Study:

• To investigate the pressure-induced phase transitions and compressibility of Cu(tcm).
• To elucidate the mechanisms behind the observed negative area compressibility (NAC) and negative linear compressibility (NLC) in Cu(tcm).

Main Methods:

• Single-crystal X-ray diffraction under hydrostatic pressure.
• Analysis of structural changes and compressibility across different pressure ranges.

Main Results:

• Cu(tcm) undergoes two phase transitions: tetragonal to orthorhombic at 0.12(3) GPa, and orthorhombic to monoclinic at 0.93(8) GPa.
• The orthorhombic phase exhibits strong NAC (-108(14) TPa⁻¹) due to framework hinge motion.
• The monoclinic phase shows slight NLC along the a-axis and zero area compressibility in the a-c plane, attributed to dampened layer rippling.

Conclusions:

• Cu(tcm) displays distinct NAC and NLC behaviors linked to its structural phase transitions.
• Understanding these mechanisms provides insights into NAC phenomena in flexible framework materials.
• The unique compressibility properties of Cu(tcm) suggest potential for novel device applications.