Predicting thermal expansion in framework compounds using a charge interaction index.

Area of Science:

• Materials Science
• Solid State Chemistry
• Computational Materials Science

Background:

• Precise control of thermal expansion is critical for industrial applications.
• Existing methods for tuning thermal expansion are limited.
• Open-framework materials offer tunable properties but require new design strategies.

Purpose of the Study:

• To develop a new parameter, the charge interaction index (CII), for predicting and controlling thermal expansion.
• To establish a link between chemical composition and thermal expansion behavior.
• To demonstrate the utility of CII in designing materials with desired thermal expansion properties.

Main Methods:

• First principles calculations to determine charge density, potential well curves, and Grüneisen parameters.
• Synthesis of novel A2M3O12 compounds with varying compositions.
• Synchrotron X-ray diffraction (XRD) as a function of temperature to experimentally measure thermal expansion.

Main Results:

• The charge interaction index (CII) was found to correlate strongly with transverse thermal vibrations and low-frequency phonon modes.
• Calculated CII values accurately predicted the thermal expansion behavior of synthesized compounds.
• In2Mo2.5W0.5O12 (minimum CII) exhibited negative thermal expansion, while (Al0.2Sc0.2Fe0.2Ga0.2Cr0.2)2W3O12 (maximum CII) showed positive thermal expansion.

Conclusions:

• The charge interaction index (CII) provides a simple and effective strategy for engineering thermal expansion in open-framework materials.
• CII offers a predictive tool for designing materials with tailored thermal expansion characteristics.
• This work opens new avenues for developing advanced materials for applications requiring precise thermal management.