Defects or Imperfections in crystalline solid can be divided into four groups namely line defects, point defects, volume defects and surface defects. Historically, crystal point defects were first regarded in ionic crystals, not in metal crystals that were much simpler..
What is crystal defect in crystallography?
crystal defect, imperfection in the regular geometrical arrangement of the atoms in a crystalline solid. These imperfections result from deformation of the solid, rapid cooling from high temperature, or high-energy radiation (X-rays or neutrons) striking the solid..
Crystal Defects control and affect a lot of properties of materials. Electric and thermal conductivity in metals can be strongly reduced by point defects whereas electric conductivity in semiconductors can be controlled by substitution defects. Ionic conductivity means vacancy defects can control the movement of ions.
Surface defects, the main two-dimensional defects, are the boundaries, or planes that separate the nanomaterials into regions with the same crystal structure but different orientations. From: Nano Today, 2020.
Jan 13, 2012Extensively revised and updated, this new edition of a classic text presents a unified approach to crystallography and to the defects found Online ISBN: 9781119961468 | First published: 13 January 2012 Author(s): Anthony Kelly, Kevin M. Knowles,
Crystallography and Crystal Defects Revised Edition A. Kelly, Churchill College, Cambridge, UK G. W. Google BooksOriginally published: 1970Author: A. Kelly
What are the effects of defects on crystal structure?
Due to this effect defects can move across the all crystal structure and also interact complicatedly
For example, a vacancy may move closer to the crystal surface, resulting to their "disappearing", or may merge to several neighboring areas and create a tilt boundary, or may simultaneously carry out both variants forming the crack
What are the problems in mathematical crystallography?
Ten problems in mathematical crystallography are presented which are chosen in the fields of crystal structure analysis, space partitions, packing of regular polytopes and balls, group theory, reduction of quadratic forms and theory of lattices
Each problem is briefly introduced and references for a more detailed study are given
Comput Math
What is crystallography and crystal defects?
The aim of the new edition of Crystallography and Crystal Defects will be to communicate the modern concepts of crystallography in a clear, succinct, manner and to put these concepts into use in the description of line and planar defects in crystalline materials, quasicrystals and crystal interfaces
Crystallography and crystal defects
Crystal type lacking 3D periodicity
Aperiodic crystals lack three-dimensional translational symmetry but still exhibit three-dimensional long-range order. In other words, they are periodic crystals in higher dimensions. They are classified into three different categories: incommensurate modulated structures, incommensurate composite structures, and quasicrystals.
Cleavage
Tendency of crystalline materials
Cleavage, in mineralogy and materials science, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye. If bonds in certain directions are weaker than others, the crystal will tend to split along the weakly bonded planes. These flat breaks are termed cleavage. The classic example of cleavage is mica, which cleaves in a single direction along the basal pinacoid, making the layers seem like pages in a book. In fact, mineralogists often refer to books of mica.
Crystal twinning
Two separate crystals sharing some of the same crystal lattice points in a symmetrical manner
Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly bonded to each other. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane.
Crystallographic defect in which atoms are displaced from their spots in the lattice
In crystallography, a Frenkel defect is a type of point defect in crystalline solids, named after its discoverer Yakov Frenkel. The defect forms when an atom or smaller ion leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location. In elemental systems, they are primarily generated during particle irradiation, as their formation enthalpy is typically much higher than for other point defects, such as vacancies, and thus their equilibrium concentration according to the Boltzmann distribution is below the detection limit. In ionic crystals, which usually possess low coordination number or a considerable disparity in the sizes of the ions, this defect can be generated also spontaneously, where the smaller ion is dislocated. Similar to a Schottky defect the Frenkel defect is a stoichiometric defect. In ionic compounds, the vacancy and interstitial defect involved are oppositely charged and one might expect them to be located close to each other due to electrostatic attraction. However, this is not likely the case in real material due to smaller entropy of such a coupled defect, or because the two defects might collapse into each other. Also, because such coupled complex defects are stoichiometric, their concentration will be independent of chemical conditions.
Crystal without defects
Crystalline materials are made up of solid regions of ordered matter. These regions are known as crystals. A perfect crystal is a crystal that contains no point, line, or planar defects. There are a wide variety of crystallographic defects.
In solid-state physics and crystallography
In solid-state physics and crystallography, a crystal structure is described by a unit cell repeating periodically over space. There are an infinite number of choices for unit cells, with different shapes and sizes, which can describe the same crystal, and different choices can be useful for different purposes.
