Giant Negative Thermal Expansion in Ultralight NaB(CN)₄

Area of Science:

• Materials Science
• Solid State Physics
• Chemistry

Background:

• Negative thermal expansion (NTE) is a rare but critical property for advanced functional materials.
• Controlling thermomechanical properties relies on understanding and engineering NTE phenomena.
• Existing NTE materials often lack ultralight characteristics, limiting their applications.

Purpose of the Study:

• To report and characterize a novel material exhibiting giant negative thermal expansion (NTE).
• To investigate the underlying mechanism responsible for the observed NTE in NaB(CN)4.
• To explore the potential of this material for applications requiring ultralight properties.

Main Methods:

• Synchrotron X-ray diffraction was employed to analyze structural changes with temperature.
• Raman spectroscopy provided insights into vibrational modes and their temperature dependence.
• First-principles calculations were utilized to model the electronic and vibrational properties.

Main Results:

• A giant NTE was observed in NaB(CN)4 across a wide temperature range (100-650 K).
• The NTE is attributed to low-frequency phonon modes, particularly non-rigid vibrations.
• The material exhibits an ultralight mass density, making it unique among NTE materials.

Conclusions:

• NaB(CN)4 is a new material demonstrating giant NTE and ultralight properties.
• Low-frequency phonon modes and negative Grüneisen parameters are key to its NTE behavior.
• This study provides fundamental insights for designing next-generation NTE functional materials.