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Order-disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder
W I F David1, R M Ibberson, S F J Cox
1ISIS Facility, CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, England.
Acta Crystallographica. Section B, Structural Science
|November 17, 2006
Summary
Researchers precisely measured the order-disorder transition in monoclinic cyclo-octasulphur using neutron powder diffraction. This critical transition, occurring at 198.4 K, indicates three-dimensional ordering in the material.
Area of Science:
- Solid-state chemistry
- Materials science
- Crystallography
Background:
- Cyclo-octasulphur (S8) exhibits complex phase transitions.
- Understanding order-disorder phenomena is crucial for materials characterization.
Purpose of the Study:
- To precisely characterize the order-disorder transition in monoclinic cyclo-octasulphur.
- To determine the critical exponent and transition temperature.
- To investigate the nature of the ordering process.
Main Methods:
- High-resolution neutron powder diffraction.
- Rapid data collection techniques.
- Geometrically constrained refinement methods for order parameter determination.
Main Results:
- A direct and precise determination of the order parameter based on molecular site occupancies.
- The transition was identified as critical and continuous.
- Transition temperature (Tc) = 198.4 (3) K.
- Critical exponent (beta) = 0.28 (3), suggesting 3D ordering.
Conclusions:
- The study provides a precise quantitative description of the order-disorder transition in monoclinic cyclo-octasulphur.
- The determined critical exponent is consistent with three-dimensional ordering models.
- Challenges related to sample thermal conductivity were noted.
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