Defects extrinsic

Intrinsic defects (or native or simply defects ) are imperfections in tire crystal itself, such as a vacancy (a missing host atom), a self-interstitial (an extra host atom in an otherwise perfect crystalline environment), an anti-site defect (in an AB compound, tliis means an atom of type A at a B site or vice versa) or any combination of such defects. Extrinsic defects (or impurities) are atoms different from host atoms, trapped in tire crystal. Some impurities are intentionally introduced because tliey provide charge carriers, reduce tlieir lifetime, prevent tire propagation of dislocations or are otlierwise needed or useful, but most impurities and defects are not desired and must be eliminated or at least controlled. 

Semiconducting Ceramics. Most oxide semiconductors are either doped to create extrinsic defects or annealed under conditions in which they become non stoichiometric. Although the resulting defects have been carefully studied in many oxides, the precise nature of the conduction is not well understood. Mobihty values associated with the various charge transport mechanisms are often low and difficult to measure. In consequence, reported conductivities are often at variance because the effects of variable impurities and past thermal history may overwhelm the dopant effects. 

Our results also shed light on the long-lived PA3 band detected in transient PM measurements of P3BT (see Fig. 7-19) and can explain changes in the PA spectra observed in several ps transient measurements of films of PPV derivatives at energies around 1.8 eV [9, 25, 60J. In good PPV films the transient PA spectrum shows a PA band of excitons at 1.5 eV whose dynamics match those of the PL and stimulated emission (SE) [9J. However, in measurements of oxidized [25] or C60-doped films 60, there appears a new PA band at about 1.8 eV whose dynamics are not correlated with those of the PL and SE. Based on our A-PADMR results here, we attribute the new PA band at 1.8 eV to polaron pair excitations. These may be created via exciton dissociation at extrinsic defects such as carbo-... 

It is the intrinsic defects that have the most interest for us, since they affect the chemical properties of the solid while extrinsic defects havelittle effect. Extrinsic defects are the proper study for those interested in the mechanics of solids, particularly metals. 

This equation arises because both of these extrinsic defects affect the energy of the crystal. We can also have grain boundaries which may be clustering of line defects or mosaic blocks. The latter may be regarded as very large grains in a crystallite. 

Lattice Vacancies and Interstitials Defects such as lattice vacancies and interstitials fall into two main categories intrinsic defects, which are present in pure crystal at thermodynamic equilibrium, and extrinsic defects, which are created when a foreign atom is inserted into the lattice. 

Extrinsic Defects Extrinsic defects occur when an impurity atom or ion is incorporated into the lattice either by substitution onto the normal lattice site or by insertion into interstitial positions. Where the impurity is aliovalent with the host sublattice, a compensating charge must be found within the lattice to pre-serve elec-troneutality. For example, inclusion of Ca in the NaCl crystal lattice results in the creation of an equal number of cation vacancies. These defects therefore alter the composition of the solid. In many systems the concentration of the dopant ion can vary enormously and can be used to tailor specific properties. These systems are termed solid solutions and are discussed in more detail in Section 25.1.2. 

Nonstoichiometric Compounds Intrinsic defects are stoichiometric defects (i.e., they do not involve any change in overall composition). Defects can also be nonstoichiometric. In the case of extrinsic defects where the host crystal is doped with aliovalent impurities, the solid so formed is a nonstoichiometric compound because the ratio of the atomic components is no longer the simple integer. There is also... 

Intrinsic and Extrinsic Defects in Insulators Ionic Conductivity... 

INTRINSIC AND EXTRINSIC DEFECTS IN INSULATORS IONIC CONDUCTIVITY... 

Heat capacities at high temperatures, T > 1000 K, are most accurately determined by drop calorimetry [23, 24], Here a sample is heated to a known temperature and is then dropped into a receiving calorimeter, which is usually operated around room temperature. The calorimeter measures the heat evolved in cooling the sample to the calorimeter temperature. The main sources of error relate to temperature measurement and the attainment of equilibrium in the furnace, to evaluation of heat losses during drop, to the measurements of the heat release in the calorimeter, and to the reproducibility of the initial and final states of the sample. This type of calorimeter is in principle unsurpassed for enthalpy increment determinations of substances with negligible intrinsic or extrinsic defect concentrations... 

Some subsequent discussion on compound 3 followed our original paper on this subject (N. Masciocchi, M. Bergamo, A. Sironi, Comments on the elusive crystal structure of 4-iodo-4 -nitrobiphenyl Chem. Comm, 1998,1347-1348 J. Hulliger, P. J. Langley, On intrinsic and extrinsic defect-forming mechanisms determining the disordered structure of 4-iodo-4 -nitrobi-phenyl Chem Comm, 1998, 2557-2558), but these papers, which describe the effects of small amounts of 4,4 -dinitrobiphenyl impurity in 3, only reinforce the idea of structures based on N02—I synthons. 

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