Anomalous high-pressure behavior of amorphous selenium from synchrotron x-ray diffraction and microtomography

Area of Science:

• Materials Science
• Condensed Matter Physics
• Geophysics

Background:

• Amorphous selenium exhibits complex behavior under high pressure, including anomalous electrical conductivity changes.
• Understanding phase transitions in amorphous materials is crucial for materials science and geophysics.

Purpose of the Study:

• To investigate the high-pressure behavior and crystallization process of amorphous selenium.
• To elucidate the mechanisms behind anomalous electrical conductivity changes under pressure.
• To develop advanced techniques for studying materials under extreme conditions.

Main Methods:

• Time-resolved diamond anvil cell synchrotron X-ray diffraction.
• Computed microtomography for in-situ analysis.
• High-pressure and high-temperature material characterization.

Main Results:

• A two-step dynamic crystallization process was observed: amorphous to monoclinic, then monoclinic to trigonal selenium.
• The transition involves local topological fluctuations and an unusual pressure-induced volume expansion.
• Metastability of intermediate phases explains the observed volume expansion.
• The study demonstrates pressure's utility in controlling and monitoring phase transitions from metastable states.

Conclusions:

• The observed crystallization mechanism explains previously reported anomalous electrical conductivity in selenium under pressure.
• The developed microtomographic technique offers a novel method for determining equations of state for amorphous materials at extreme conditions.
• This research highlights the potential for creating new material phases from highly metastable states using controlled pressure.