Compensation defect

In cases where the antisite defects are balanced, such as a Ga atom on an As site balanced by an As atom on a Ga site, the composition of the compound is unaltered. In cases where this is not so, the composition of the material will drift away from the stoichiometric formula unless a population of compensating defects is also present. For example, the alloy FeAl contains antisite defects consisting of iron atoms on aluminum sites without a balancing population of aluminum atoms on iron sites. The composition will be iron rich unless compensating defects such as A1 interstitials or Fe vacancies are also present in numbers sufficient to restore the stoichiometry. Experiments show that iron vacancies (VFe) are the compensating defects when the composition is maintained at FeAl. 

The electron concentration in donor-doped TCOs becomes compensated with increasing oxygen partial pressure. The nature of the compensating defect thereby depends on the material. As mentioned earlier, compensation of n-type doping in ZnO occurs by introduction of zinc vacancies. In contrast, compensation in 1 03 is accomplished by oxygen interstitials [117], Their importance in Sn-doped 1 03 has been already pointed out by Frank... 

The defects which are induced in doped a-Si H reduce the dopant formation energy by providing electronic compensation. Defects are no longer needed to lower the energy when a-Si H is doped with both boron and phosphorus. Instead charged dopant states result from the reaction... 

Ferroelectric materials in this family have the perovskite crystal structure, where Ti+4(Zr+4) is in the B site at the center of the unit cell within an octrahedral coordination of O-2, and Pb+2 (La+3) occupies the A site at cube corners. Considerable discussion and experimentation have occurred to decide what charge-compensating defects are created by the... 

Subsequent steps in trapping that are particularly important to the photographic process include the dynamic ionic stabilization of deep trapping centers by mobile charge-compensating defects [118] and/or non-radiative recombination at the defect center [119]. 

The doping, and in particular, the mode of solution, of dopant ions are of crucial importance in these materials due to the extrinsic control of the charge carriers, which has already been stressed. As an example, we consider + 1 and + 2 cation dopants in La2Cu04. Table 10.4 contains calculated solution energies for the two possible substitution reactions, bearing in mind that holes are the preferred compensating defect ... 

Valency factor. The two end members must have the same valence. If this condition is not satisfied, compensating defects form in the host crystal in order to maintain charge neutrality. Given that the entropy increase associated with defect formation is not likely to be compensated for by the energy required to form them over the entire composition range, complete solid solubility is unlikely. 

As with lead azide, impurities were found to alter photodecomposition rates in AgNa [237]. The addition of Pb " retarded the gas evolution rate while CO2 enhanced it. No explanation for the effect was given, but it may involve changes in stoichiometric charge-compensating defects. The authors claim that photolysis is not concentrated in disordered regions of the crystal as is observed for lead and thallous azides (see Section D). 

The MCI2 (M = Ca, Sr, and Ba) crystals are ideal candidates for studies of the spectroscopic properties of Tm " ions. First, no charge-compensation defects are required after thulium ions are introduced into these hosts. Second, there is reliable experimental information about the absorption/emission spectra of these materials [2-8]. Moreover, the earth-alkaline halides are also important from an application point of view because the laser action has been achieved in CaF2 Tm [9]. The spectra of Tm " were modeled in our earlier publication [10]. 

Write a reaction for dissolution of protons in an oxide with water vapour as source and with oxygen interstitials as compensating defects. 

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