Medium-range atomic correlation in simple liquids. I. Distinction from short-range order.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Physical properties of liquids and glasses depend on atomic-level ordering.
• Short-range order (SRO) describes nearest-neighbor interactions.
• Medium-range order (MRO) describes correlations beyond nearest neighbors.

Purpose of the Study:

• To investigate the role of MRO in the glass transition of simple liquids.
• To understand MRO as a descriptor of point-to-set atomic correlation.
• To explore the relationship between MRO, SRO, and liquid viscosity.

Main Methods:

• Analysis of X-ray diffraction data.
• Computer simulations using classical potentials.
• Examination of the pair-distribution function's peaks.

Main Results:

• The third peak of the pair-distribution function (representing MRO) shows a distinct change in temperature dependence at the glass transition.
• The first peak (representing SRO) changes smoothly through the glass transition.
• MRO freezing, not SRO freezing, appears to induce the glass transition.

Conclusions:

• The glass transition is primarily governed by the freezing of medium-range order.
• Medium-range order plays a crucial role in determining the viscosity of supercooled liquids.
• MRO is a key factor in understanding the behavior of liquids approaching the glassy state.