Local order and long-range order

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Short-range order and long-range order describe order aspects of the arrangement of atoms or molecules in liquids and solids . Such considerations are particularly relevant in physical chemistry and crystallography or solid state physics . While the short-range order relates to the spatial arrangement of the next, perhaps the next but one, particle of the substance, a long-range order requires a repetitive arrangement of the particles over numerous repetitions.

Local order

Short-range order is a regular grouping of particles only in the vicinity of a reference particle. However, with distance, the order can decrease, for example for a molecule in a liquid or an atom in an amorphous solid . The bond lengths and angles to the nearest neighbors are mainly used to describe the order .

We find the ideal case of a pure short-range order in liquids in which the particle distances ( atomic or molecular distances) are constant and the bond angles fluctuate strongly. There is almost no correlation of the bond angles with the next but one neighbor .

The entire spectrum of materials between pure short-range order and long-range order occurs in nature.

Long-range order

As long-range order is called the regular and periodic arrangement ( "to the distance") of molecules or atoms in a crystalline solid state , in particular in intermetallic phases .

Solids without long-range order are called amorphous solids such as glass and supercooled melt. Like liquids, they only have a short-range order.

The structure of real crystals deviates from an ideal long-range order in many places. Real crystals - also called crystallites - contain a large number of crystal defects without losing their long-range order character.

States of order in solids

Schematic representation: short-range to long-range order in solids
Status Range of order example
amorphous (local order) next and next but one particle Glass
nanocrystalline Nanometer Paracrystal
micro crystalline Micrometer quartz
polycrystalline millimeter Polycrystalline diamond
monocrystalline (long-range order) centimeter monocrystalline ingots

Individual evidence

  1. Ludwig Bergmann, Rainer Kassing, Clemens Schaefer, with Stefan Blügel: 6. Textbook of Experimental Physics solids . Walter de Gruyter, 2005, ISBN 978-3-11-017485-4 , p. 691.