Nanoscale Engineering of Polymorphism in Cu₂Se-Based Composites.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• Controlling crystal polymorphism is crucial for tuning phase-change material properties.
• Metastable polymorphs offer unique functional characteristics.
• Stabilizing specific phases under ambient conditions remains a significant challenge.

Purpose of the Study:

• To stabilize the superionic β-Cu₂Se phase under ambient conditions.
• To achieve direct control over the α-Cu₂Se and β-Cu₂Se polymorph ratio in composites.
• To investigate the impact of controlled polymorphism on charge and heat transport.

Main Methods:

• Synthesis of (x)CuGaSe₂/(1-x)Cu₂Se composites using CuGaSe₂ nanoseeds.
• Utilizing the lattice mismatch between β-Cu₂Se and CuGaSe₂ for preferential phase stabilization.
• Characterization of composite microstructure and transport properties.

Main Results:

• Successful stabilization of the β-Cu₂Se phase under ambient conditions.
• Demonstrated control over the relative abundance of α-Cu₂Se and β-Cu₂Se polymorphs.
• Observed a significant decoupling of charge and heat transport in the composites.
• Breakdown of the Wiedemann-Franz law due to hierarchical microstructure.

Conclusions:

• CuGaSe₂ nanoseeds effectively promote the formation and stabilization of the β-Cu₂Se phase.
• The developed composite structure allows for independent tuning of electrical and thermal conductivity.
• This approach offers a novel pathway for designing advanced thermoelectric materials.