Grain boundary activation energy

It can be seen drat the major difference lies in die activation energy being lower in the grain boundary. Data for a number of metals show that the activation energy for grain boundary diffusion is about one-half of that for volume diffusion. 

Here p is the density, a is the particle size, C and n are constants, Q is the activation energy for sintering, R is the gas constant and T is the absolute temperature, n is typically about 3, and Q is usually equal to the activation energy for grain boundary diffusion. 

The fabrication procedure affects the product s microstructure including grain size, grain-boundary width, and porosity. In addition, different procedures introduce various amounts of impurities to the product. Therefore, the electrical conductivity and activation energy are affected by the fabrication procedure since, as mentioned above,... 

However, the derived value for Ei is usually termed the activation energy E and may contain other contributions in addition to the intrinsic Ei value, such as those arising from the orientation and morphology of the sample. For this reason E is most commonly used. In the case of polycrystalline thin hlms, grain boundaries may have a dominant effect, as will be discussed in Section 6.4, where examples of intrinsically metallic materials behaving as semiconductors will be given. 

In recent years, Burke and coworkers have found [373] that severe cathodization of pc-Au in acid solution resulted in the appearance of faradaic responses in the double-layer region. Such anomalous behavior may be explained by the presence of active gold atoms on the electrode surface. These active atoms appear as a result of the pretreatment process, when the part of inserted energy into the gold sample is retained mosdy by the surface atoms and atoms of the outer layers, in the form of various types of defects, for example, adatoms, vacancies, grain boundaries, and others. 

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