Time-resolved X-ray powder diffraction using a large-area CCD-based detector and Rietveld refinement: solid-state...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Polymerization Kinetics

Background:

• Polysulfur nitride [(SN)x] is a conductive polymer with unique properties.
• Understanding its formation mechanism is crucial for material synthesis.
• Solid-state polymerization offers a controlled route to polymer formation.

Purpose of the Study:

• To investigate the kinetics of solid-state polymerization of disulfur dinitride (S2N2) to polysulfur nitride [(SN)x].
• To characterize the structural changes during polymerization using in-situ X-ray diffraction.
• To identify potential byproducts or alternative phases formed during polymerization.

Main Methods:

• Utilized monochromatic high-energy synchrotron X-ray powder diffraction (lambda = 0.3263 A).
• Employed a large-area CCD-based X-ray image-intensifier detector for rapid data acquisition.
• Applied Rietveld refinement for quantitative analysis of diffraction patterns from 2-second exposures.

Main Results:

• Successfully monitored the polymerization of S2N2 to (SN)x at a rate of two images per minute.
• Observed significant lattice distortions in S2N2 prior to polymerization, with a 1% decrease in the 'a' axis and a 1% increase in the 'c' axis at 50% conversion.
• Rietveld refinement provided accurate scale factors and cell parameters for both S2N2 and beta-(SN)x throughout the process.
• Identified the formation of the expected beta-(SN)x polymer along with a minor amount of another (SN)x phase.

Conclusions:

• The solid-state polymerization of S2N2 to (SN)x is a kinetically controllable process.
• Lattice distortion is a key precursor to the polymerization reaction.
• The polymerization can yield multiple phases of (SN)x, necessitating further investigation into the secondary phase.