DEFECT

Defect

To dispel the misleading attention to perfect crystals, in Chapter 4 on defects in solids 

we look at different kinds of defects. The definitions for several of the more common 

material defects are discussed. It has been found over and over that simple structural 

defects such as substitutional and interstitial defects can alter electrical properties and 

mass transport via diffusion by orders of magnitude,while at the same time hardly affect 

the melting point or the thermal conductivity for a material. Furthermore line defects 

are implicated as the main factor in the plastic deformation of crystalline materials.The 

notion of grain boundaries as the boundaries in between single crystal grains is also 

implicated in the mechanical properties of materials and in electronic properties of poly- 

crystalline semiconductors. Thus both the structure and its level of perfection provide a 

backdrop from which the behavior and properties of a material are understood, partic- 

ularly, electronic materials. 

Also in Chapter 4 another fundamental tenet of materials science is introduced and 

used liberally in following chapters.This tenet is the Boltzmann distribution from which 

both equilibrium thermodynamics and activation energies, or energy barriers, for 

processes can be understood. This concept is introduced by considering a simple two 

allowed state problem,and assessing how two energetically distinct states separated by a 

difference in energy, DE, can be populated. The result is a familiar exponential 

term e-DE/kToften referred to as the Boltzmann factor. However, in the field of chemical 

kinetics an Arrhenius factor with the same form as the Boltzmann factor is often dis- 

cussed in relation to the velocity of chemical reactions, but the Arrhenius factor is often 

introduced without adequate discussion about its origin,or at best as an empirical result. 

The importance of this idea is such that it is introduced and discussed early in the text. 

Furthermore the laws of thermodynamics derive from the average or statistical nature of 

atoms or compounds that comprise a material. This statistical notion is crucial toward 

the understanding the average properties of a macroscopic piece of a material 

that contains a large number of atoms and/or molecules. Such thermodynamics proper- 

ties include the phase of the material, the vapor pressure, and decomposition tempera- 

ture. On the other hand, quantum mechanics may be required to understand the 

properties that depend on the specific interactions of atoms and/or molecules within a 

material such as the absorption or emission of light and the electronic and thermal 

conductivity. 

Ramon A. Carmona C

C.I 17646653

CRF

http://media.wiley.com/product_data/excerpt/71/04716959/0471695971.pdf

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