Tunable thermal expansion in framework materials through redox intercalation.

Area of Science:

• Solid-state chemistry
• Materials science
• Condensed matter physics

Background:

• Controlling thermal expansion in solids is crucial for many applications but remains challenging.
• Framework materials often exhibit negative thermal expansion (NTE) when voids are empty, and positive thermal expansion (PTE) when filled.
• Existing methods for tuning thermal expansion are limited.

Purpose of the Study:

• To investigate redox intercalation as a novel method for controlling thermal expansion.
• To demonstrate the tunability of thermal expansion in a negative thermal expansion framework material.

Main Methods:

• Redox intercalation of lithium (Li) ions into scandium fluoride (ScF3) doped with iron (Fe).
• Investigation of the structural and thermal expansion properties of the modified ScF3 material.

Main Results:

• Successful insertion of Li ions into the ScF3:Fe framework via redox intercalation.
• Demonstrated control over thermal expansion, achieving positive, zero, and negative values.
• Identified steric hindrance of transverse fluoride ion vibrations as the key mechanism for thermal expansion control.

Conclusions:

• Redox intercalation is an effective strategy for precisely controlling the thermal expansion of framework materials.
• This method offers a general approach applicable to many known framework materials exhibiting phonon-driven negative thermal expansion.
• The findings open new avenues for designing materials with tailored thermal expansion properties.