Crystalline Defects:
Crystalline defect is the lattice irregularity having one or more of its dimensions on order of atomic dimension. There are five main categories of crystalline defects:
Point Defects:
There are two main kinds of geometrical defects in the crystal. There are those which are much localized and are of atomic dimensions. These are known as point defects. Example of this is impurity atom that can be either substitutional or interstitial impurity.
i) When some atoms are not accurately in their right place, lattice is said to have imperfections or defects.
ii) Several properties of solids e.g. electrical resistance and mechanical strength are run by presence of certain kinds of defects in lattice.
Point defects permit for diffusion to happen in solid state. There are different categories of point defects:
a) Vacancy:
These are created by thermal vibrations of crystal lattice and/or from need to maintain charge neutrality.
b) Self-interstitial or interstitialcy:
A position on crystal lattice which is not usually occupied is known as interstitial site. If it is occupied by same atomic species it is self-interstitial or self-interstitialcy. It produces large distortions in crystal lattice and so concentrations are small.
c) Impurities:
i) Less than 15% difference in atomic radii
ii) Same crystal structure
iii) Similar electronegativities
iv) Same valence.
d) Schottky defect: a pair of oppositely charged ion vacancies.
e) Frenkel defect: a vacancy-interstitialcy combination.
Linear Defects (Dislocations):
Unlike point defects, these are kinds of disorder that extend beyond volume of one or two atoms. It is line defect that can extend right through crystal or it can form closed loops.
Line defect is lattice distortion created about line formed by solidification process, plastic deformation, vacancy condensation or atomic mismatch in solid solutions. Dislocations describe observation of plastic deformation at lower stress than would be needed in perfect lattice. They also describe phenomenon of work hardening. There are two basic kinds of dislocations, edge dislocation and screw dislocation.
Edge dislocation:
These are caused by termination of the plane of atoms in middle of crystal. In such a case, adjacent planes are not straight, but instead bend around edge of terminating plane so that crystal structure is completely ordered on either side. Analogy with stack of paper is appropriate: if half a piece of paper is put in the stack of paper, defect in the stack is only visible at the edge of half sheet.
Screw dislocation:
This is more hard to visualize, but basically includes structure in which helical path is traced around linear defect (dislocation line) by atomic planes of atoms in crystal lattice.
Planar (Interfacial) Defects:
External surfaces:
Atoms at any surface are not in their perfect crystal positions as they will have decrease number neighbors than atoms inside volume of material. Therefore, the atoms will be at higher energies. During solidification, materials attempt to minimize this.
Grain boundaries:
Grains are produced during solidification procedure. The grain boundary is area of mismatch between volumes of material which have a common orientation of crystallographic axes. Atoms at grain boundaries are not in their perfect crystal positions and therefore, grain boundary is less dense. These atoms are at higher energies than atoms inside the volume of grain. Thickness is of order of 2-5 atoms wide.
There are different categories of grain boundaries:
At ambient temperatures, grain boundaries give strength to the material. So in general, fine grained materials are stronger than coarse grained ones as they have more grain boundaries per unit volume. Though, at higher temperatures, grain boundaries act to weaken the material because of corrosion and other factors. Grain size can be measured by:
The size and shape of grains are estimated by number of factors during solidification:
Many materials are polycrystalline (or polygranular). There are some applications where expense and time to generate single crystal materials (and therefore no grain boundaries) is justified:
Volume (Bulk) Defects:
These are introduced during processing and fabrication.
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online physics tutoring. Chat with us or submit request at [email protected]
www.tutorsglobe.com offers properties of aldehydes and ketones homework help, properties of aldehydes and ketones assignment help, online tutoring assistance, organic chemistry solutions by online qualified tutor's help.
Ionic equilibria in weak acids and bases tutorial all along with the key concepts of Determination of Ka, Polyprotic acids, Weak Bases, pH of a salt solution, Buffers, Titration Curves
No matter how complicated your task is; our professional Restorative Justice Assignment Help service always offers precise solutions.
online ged exam preparation course and online ged tutoring package offered by TutorsGlobe are the most comprehensive and customized collection of study resources on the web, offering best collection of ged practice papers, quizzes, ged test papers, and guidance.
Friction in Solids and Liquids tutorial all along with the key concepts of Concept of Friction, Merits and Demerits of Friction, Reasons for Reducing Friction, Types of Friction, Laws of Friction, Coefficient of friction and Concept of Viscosity
tutorsglobe.com mechanism of breathing assignment help-homework help by online respiration tutors
tutorsglobe.com dynamics of filtration assignment help-homework help by online excretion tutors
Interference by division of Amplitude tutorial all along with the key concepts of Stroke's analysis of phase change, Interference in thin films, Interference by a wedge-shaped film and Newton's Ring
Sexual Selection for Cultural Displays tutorial all along with the key concepts of cultural anthropology, Sexual selection theory, Sexual selection for indicators and cultural courtship model
origin, evolution and structure of galaxies tutorial all along with the key concepts of active galactic nuclei, galaxy properties and correlations, classification of galaxies and cosmic structure formation
Steps of activity based costing - The costing system that is already existing should be capable to adopt the activity based costing system that is why product costs can be precisely determined and correct pricing decisions can be taken in a competitive business environment.
Theory and lecture notes of The main sources of error all along with the key concepts of functions and data, Truncation Error, Round-off Error, Loss of Precision, Bad Conditioning. Tutorsglobe offers homework help, assignment help and tutor’s assistance on The main sources of error.
Structure and Function of Membranes tutorial all along with the key concepts of Structure of Membranes, Functions of Membranes, Movement of Water through Membranes, Water Potential, Osmosis and Turgor
Factors Affecting Strengths of Acids-Bases tutorial all along with the key concepts of Inductive effect, acidity of ethanoic acid, substitution X electron withdrawing, substituent X electron donating
tutorsglobe.com adrenal medulla assignment help-homework help by online co-ordination systems tutors
1958037
Questions Asked
3689
Tutors
1482986
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!