Isotropic Zero Thermal Expansion in (Sc_0.85Al_0.1Cr_0.05)F₃

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Zero thermal expansion materials, exhibiting the Invar effect, are crucial for high-precision equipment.
• Understanding the mechanisms behind zero thermal expansion is key to designing advanced materials.

Purpose of the Study:

• To synthesize and characterize a novel zero thermal expansion fluoride material.
• To elucidate the underlying mechanism of zero thermal expansion in the synthesized material.

Main Methods:

• Solid-state reaction method for material synthesis.
• Variable-temperature X-ray diffraction and pair distribution function analysis.
• Density functional theory (DFT) calculations.

Main Results:

• A new zero thermal expansion material, (Sc0.85Al0.1Cr0.05)F3, was successfully prepared with a linear thermal expansion coefficient of -0.83 × 10⁻⁶ K⁻¹ between 173-473 K.
• Local structural distortions induced by Al and Cr incorporation were identified, influencing fluorine atom vibrational modes.
• DFT calculations confirmed a weighted sum of the Grüneisen parameter near zero, consistent with observed zero thermal expansion.

Conclusions:

• The study presents a new fluoride-based zero thermal expansion material.
• The findings reveal the structure-property relationship governing thermal expansion in this material, highlighting the role of local distortions and vibrational modes.