Joe Zaug
Chemistry and Materials Division,
Lawrence Livermore National
Laboratory
Abstract:
"Conclusive"
evidence for the existence of pressure induced polyamorphic transitions
only exists for two systems: liquid phosphorus and supercooled water.
As part of a search for additional occurrences we discovered a third
polyamorphic transition in amorphous red phosphorus (aRP). A
high-pressure aRP phase was quenched at ambient conditions and is found
to be denser than the original phase where intermediate-range order (IRO)
exists. Inverse Monte-Carlo (IMC) analysis constrained by x-ray
diffraction data (obtained from a unique ultra wide aperture diamond
anvil cell) and Raman data shows that the transition begins with P9
cages scattered throughout a 3-coordinate covalently bonded random
phosphorus atom. At a specific pressure the
periodic coherence of P9 cage volume or perhaps the
interstitial void space, weakens while the network structure uniformly
collapses with hydrostatic compression. The high-pressure aRP
phase exhibits a significantly less intense first strong diffraction
peak (FSDP) thus indicating less IRO. Fragments of the original ambient
pressure 3-coordinate structural framework exhibit similarities to
Hittorf’s phosphorus, albeit with no long-range atomic order. Details
concerning data collection, normalization, and analysis using IMC
simulations will be presented together with results from computed
changes in average atomic structural parameters (bond lengths, bond
angles, distribution of coordination numbers) across the
pressure-induced transition.
This work was partially performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-Eng-48.
abstract (pdf)
2008 Run
Nov 19th - Dec 22nd
