Classical and nonclassical germanium environments in high-pressure BaGe5.

Area of Science:

• Materials Science
• Solid-State Chemistry
• High-Pressure Physics

Background:

• Barium germanides are intermetallic compounds with diverse structural and electronic properties.
• Understanding their behavior under high pressure is crucial for exploring novel material phases.

Purpose of the Study:

• To synthesize and characterize a new crystalline form of BaGe5 at high pressure.
• To elucidate the crystal structure, chemical bonding, and physical properties of this novel phase.

Main Methods:

• High-pressure synthesis using a diamond anvil cell.
• Single-crystal electron diffraction and powder X-ray diffraction for structural determination.
• Quantum chemical calculations for bonding analysis.
• Electrical resistivity and magnetic susceptibility measurements for property evaluation.

Main Results:

• A new body-centered orthorhombic structure (Imma) of BaGe5 was obtained at 15 GPa and 1000-1200 K.
• The structure features complex Ge layers with varying Ge-Ge bond lengths and Ba atoms coordinated by 15 Ge neighbors.
• Charge transfer from Ba to Ge was observed, with Ge atoms exhibiting oxidation states near 0 and 1-.
• The compound exhibits metallic conductivity (240 μΩ cm at 300 K) and diamagnetic behavior.

Conclusions:

• The high-pressure synthesis successfully yielded a novel crystalline phase of BaGe5.
• The structural and electronic properties indicate a complex interplay of covalent and ionic bonding within the germanide framework.
• This study expands the known phase diagram of Ba-Ge compounds and highlights the potential for discovering new materials under extreme conditions.