Negative and Zero Thermal Expansion in High-Entropy NASICON Structure Oxide Material

Area of Science:

• Materials Science
• Solid State Chemistry

Background:

• Zero thermal expansion (ZTE) materials are crucial for precision components, enhancing stability and lifespan.
• Developing materials with tunable thermal expansion is vital for advanced technological applications.

Purpose of the Study:

• To design and synthesize a novel high-entropy material with anomalous thermal expansion properties.
• To investigate the mechanisms behind negative thermal expansion (NTE) and ZTE in the designed material.

Main Methods:

• High-entropy synthesis strategy applied to create KMg1/3Mn1/3Co1/3Sc1/2In1/2Mo3O12 with a NASICON structure.
• Characterization of thermal expansion behavior using temperature-dependent measurements.
• Analysis of crystal structure and vibrational dynamics using temperature-dependent Raman spectroscopy.

Main Results:

• The synthesized material KMg1/3Mn1/3Co1/3Sc1/2In1/2Mo3O12 exhibits volumetric negative thermal expansion (NTE) below 300 K (αV = -9.97×10⁻⁶ K⁻¹).
• Achieved near-zero thermal expansion (ZTE) between 300-700 K (αV = 1.56×10⁻⁶ K⁻¹).
• Anisotropic oxygen atom vibrations driving polyhedral rotation were identified as the origin of NTE.

Conclusions:

• Anomalous thermal expansion arises from the interplay between polyhedral bending vibrations and K⁺ ion vibrations.
• Polyhedral coupled rotation is confirmed as a key factor in the material's anomalous thermal expansion.
• The high-entropy strategy provides a viable route for designing NTE and ZTE materials.