BaGe6 and BaGe(6-x): incommensurately ordered vacancies as electron traps.

Area of Science:

• Solid-state chemistry
• Materials science
• High-pressure physics

Background:

• Germanium-based framework compounds are of interest for their unique structural and electronic properties.
• Understanding the synthesis and stability of these materials under extreme conditions is crucial for discovering new functionalities.

Purpose of the Study:

• To report the synthesis of novel germanium-based framework compounds, BaGe6 and BaGe(6-x).
• To investigate the structural characteristics and electronic properties of these metastable compounds.

Main Methods:

• High-pressure, high-temperature synthesis techniques were employed (15 GPa, 1073 K for BaGe6; 10 GPa, 1073 K for BaGe(6-x)).
• Structural analysis involving incommensurate modulations and defect characterization.
• Bonding analysis in direct space and physical measurements of transport properties.

Main Results:

• Successful synthesis of metastable BaGe6 and BaGe(6-x) compounds.
• BaGe(6-x) exhibits partial network fragmentation with modulated atomic positions and site occupancy.
• Defect formation in BaGe(6-x) is linked to free electron pairs, resulting in semiconducting behavior and low thermal conductivity.

Conclusions:

• The study demonstrates the feasibility of synthesizing novel germanium frameworks under high pressure.
• The defective BaGe(6-x) compound presents interesting electronic and thermal properties due to its unique defect structure.
• These findings open avenues for exploring germanium-based materials for thermoelectric or electronic applications.