Defects temperature dependence

The color development of photochromic compounds can also be utili2ed as a diagnostic tool. The temperature dependence of the fa ding of 6-nitroindolinospiropyran served as the basis for a nondestmctive inspection technique for honeycomb aerospace stmctures (43). One surface of the stmcture to be exarnined was covered with a paint containing the photochromic compound and activated to a violet color with ultraviolet light. The other side of the stmcture was then heated. The transfer of heat through the honeycomb stmcture caused bleaching of the temperature-dependent photochromic compound. Defects in the honeycomb where heat transfer was inhibited could be detected as darker areas. 

Several points are worth noting about these formulae. Firstly, the concentrations follow an Arrhenius law except for the constitutional def t, however in no case is the activation energy a single point defect formation energy. Secondly, in a quantitative calculation the activation energy should include a temperature dependence of the formation energies and their formation entropies. The latter will appear as a preexponential factor, for example, the first equation becomes... 

What is the nature of the defects seen in the EPR spectra For alkali and alkali earth halogenides it is well known that irradiation with X-ray, neutrons, gamma-radiation, or electrons produce paramagnetic color centers (F-center) [109-111]. If these centers are created in large amounts, they can be stabilized by the formation of metal clusters as observed for MgCl2 films after prolonged electron radiation [106]. From the temperature dependence... 

Fig. 1.27 The temperature dependence of observed changes in surface-adjacent area of conductivity Act and work functions A > for Ti02 (110) with defects caused by interaction with molecular oxygen [184]...

Since the number of phonons increases with temperature, the electron-phonon and phonon-phonon scattering are temperature dependent. The number of defects is temperature independent and correspondingly, the mean free path for phonon defect and electron defect scattering does not depend on temperature. 

In this temperature range, the number of phonons is small, and their scattering is due to lattice defects or to crystal boundaries. Of the two processes of scattering, the latter is of more importance since, at low temperatures, the dominant phonon wavelength is larger than the size of the lattice imperfections. As a consequence Aph is usually temperature independent. Hence, the temperature dependence of the thermal conductivity is that of the specific heat ... 

The sequence of low conductance values L is attributed to isomers of alkanedithiols with gauche defects. This interpretation is also supported by the experimentally observed temperature dependence of L conductance values. The alteration of gauche states appears to be an activated process [244]. 

Chapter 2) and cannot be eliminated from the solid. They are called intrinsic point defects. This residual population is also temperature dependent, and, as treated later (Chapter 2), heating at progressively higher temperature increases the number of defects present. 

An important result is also that many approximants of these quasicrystalline phases have similar conduction properties. For example the crystalline a-AlMnSi phase with a unit cell size of about 12 A and 138 atoms in the unit cell has a conductivity of about 300(Qcm) at low temperature [7,9]. The conductivity has the same defect and temperature dependence as that of the AlCuFe and AlPdMn icosahedral phase. There is, to our knowledge, no experimental result on the optical conductivity of this a-AlMnSi phase, but it is very likely that it is similar to that of AlCuFe and AlPdMn icosahedral phase. 

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