Unexpected compound reformation in the dense selenium-hydrogen system.

Area of Science:

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

Background:

• H2Se and (H2Se)2H2 compounds are unstable under compression above 22 GPa.
• Previous research on chalcogen hydrides at high pressures indicated potential for novel compound formation.

Purpose of the Study:

• To investigate the high-pressure phase behavior of selenium hydride.
• To synthesize and characterize new selenium-hydrogen compounds under extreme conditions.

Main Methods:

• High pressure-high temperature diamond anvil cell experiments.
• X-ray diffraction for structural analysis.
• Density functional theory calculations for structural validation.
• Electrical resistance measurements.

Main Results:

• A novel compound, SeH2(H2)2, was synthesized above 94 GPa.
• X-ray diffraction revealed a tetragonal (I41/a m d) structure with zig-zag H-Se chains and H2 molecules in Se interstices.
• Density functional theory calculations confirmed the structure with minor distortions.
• Electrical resistance measurements showed SeH2(H2)2 is non-metallic up to 148 GPa.
• No compound formation was observed in the Te-H system up to 165 GPa and 2000 K.

Conclusions:

• The high-pressure phase behavior of chalcogen hydrides is unique and complex.
• SeH2(H2)2 represents a novel high-pressure phase with a distinct crystal structure.
• The findings challenge previous assumptions about the predictability of high-pressure behavior in these systems.