# Paracrystalline

﻿
Paracrystalline

Paracrystalline materials are defined as having short and medium range ordering in their lattice (similar to the liquid crystal phases) but lacking long range order. [Voyles, et al. Structure and physical properties of paracrystalline atomistic models of amorphous silicon. "J. Ap. Phys.", 90(2001) 4437, doi: 10.1063/1.1407319] .

Ordering is the regularity in which atoms appear in a predictable lattice, as measured from one point. In a highly ordered, perfectly crystalline material, or single crystal, the location of every atom in the structure can be described exactly measuring out from a single origin. Conversely, in a disordered structure such as a liquid or amorphous solid, the location of the first and perhaps second nearest neighbors can be described from an origin (with some degree of uncertainty) and the ability to predict locations decreases rapidly from there out. The distance at which atom locations can be predicted is referred to as the correlation length $xi$. A paracrystalline material exhibits correlation somewhere between the fully amorphous and fully crystalline.

The primary, most accessible source of crystallinity information is X-ray diffraction, although other techniques may be needed to observe the complex structure of paracrystalline materials, such as fluctuation electron microscopy [Biswas, P, et al. "J. Phys.:Condens. Matter", 19 (2007) 455202, doi:10.1088/0953-8984/19/45/455202 ] in combination with Density of states modeling [Nakhmanson, Voyles, Mousseau, Barkema, and Drabold. "Phys. Rev. B" 63(2001) 235207. doi: 10.1103/PhysRevB.63.235207] of electronic and vibrational states.

Paracrystalline Model

The paracrystalline model is a revision of the Continuous Random Network model first proposed by W. H. Zachariasen in 1932 [Zachariasen, W.H., "J. Am. Chem. Soc.," 51(1932) 3841.] . The model is defined as highly strained, microcrystalline grains surrounded by fully amorphous material [J.M. Cowley, Diffraction Studies on Non-Cryst. Substan. 13 (1981)] . This is a higher energy state then the continuous random network model. The important distinction between this model and the microcrystalline phases are the lack of defined grain boundaries and highly strained lattice parameters, which makes calculations of molecular and lattice dynamics difficult.

Applications of the Model

The paracrystalline model has been useful in describing the state of partially amorphous semiconductor materials after deposition.

References

ee also

* Amorphous solid
* Single Crystal
* Polycrystalline
* Crystallography

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• paracrystalline — para·crystalline …   English syllables

• paracrystalline — adjective see paracrystal …   Useful english dictionary

• Hirano bodies — Paracrystalline inclusions found in the brain of patients with neurodegenerative disorders …   Dictionary of molecular biology

• Molecular models of DNA — While this purified DNA precipitated in a water jug (left) appears to be a formless mass, nucleic acids actually possess intricate structure at the nanoscale (right). M …   Wikipedia

• Nanotechnology — Part of a series of articles on …   Wikipedia

• Nanocrystalline silicon — Main article: Silicon thin film cell Silicon nanopowder Nanocrystalline silicon (nc Si), sometimes also known as microcrystalline silicon (μc Si), is a form of porous silicon.[1] It is an allotropic form of silicon wi …   Wikipedia

• Methanogen — Methanopyrus kandleri Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria. They are common in wetlands, where they are responsible …   Wikipedia

• Single crystal — A huge KDP crystal grown from a seed crystal in a supersaturated aqueous solution at LLNL which is to be cut into slices and used on the National Ignition Facility for frequency doubling and tripling. A single crystal or monocrystalline solid is… …   Wikipedia

• Raymond Gosling — (born 1926) is a distinguished scientist who worked with both Maurice Wilkins and Rosalind Franklin at King s College London in deducing the structure of DNA, under the direction of Sir John Randall.Early yearsHe was born in 1926 and attended… …   Wikipedia

• Cerebroside — Cerebrosides is the common name for a group of glycosphingolipids called monoglycosylceramides which are important components in animal muscle and nerve cell membranes. They consist of a ceramide with a single sugar residue at the 1 hydroxyl… …   Wikipedia