Defects anti-site disorder

It is important to note that the samples of LixMn2(Mo04)3, nanoscaled samples, synthesized by solvothermal method are free from the anti-site disorder resonance signal, which is observed in micro-scaled Li2Mn2(Mo04)3 samples. The appearance of antisite disorder defects is associated with location of Mn + in lithium interstitial positions. It impedes the diffusion of Li+ in crystal structure of cathodic materials that have the negative influence on their electrochemical performance. Thus, the ESR investigations... 

Pairs of interstitials have not been found as a dominant defect structure. Anti-site disorder (swapping of sites) is common in intermetaUics and between cations on different sites (or anions on different sites). However, swapping between cations and anions in ionic compounds is mostly prohibited by the very unfavourable effective charges that would arise. 

Nonidealities also occtu in YBa2Cu30e+x, the most popular high temperature superconductor (x>0.5). Here anti-site disorder effects are of importance, in addition to associates. Defects of type generated during preparation and then frozen-in, formally take the same role as added aliovalent doping (see also metal vacancies in SrTiOa) [187]. At low temperatures ordering processes are of significance. 

Anti-Frenkel disorder similar to Frenkel disorder except that the interstitials are anions and vacancies are therefore in the anion sublattice. In Zr02 the reaction is 0 kS + 0[ and the anti-Frenkel equilibrium constant is K p = [ko ][On- This type of thermal defect is found in lattices that have a fluorite structure (CaF2, Zr02), which means that there are many large interstitial sites where the anions can be accommodated, but not the cations because their charge is larger, and they are less well screened from each other. 

A solid is said to be stoichiometric if the ratio of the quantities of the two elements A and B remains constant and equal to its theoretical value in the perfect crystal. The ratio between the number of sites of A and the number of sites of B also remains constant. These two constants mean that we must have at least two types of defects occurring simultaneously. This set of two defects present simultaneously is known as a disorder. We can see from the list of defects set out above that there are six classes of disorders with two defects, which are classified into two groups symmetrical disorders and anti-symmetrical disorders. In practice, we find only four types of disorders with two defects. 

Since there seems to be nonactive cross-reacting hexosaminidase protein to antibodies prepared against hexosaminidases A and B and to specific anti-A antibodies (Srivastava and Beutler, 1973), it seems likely that the basic defect in this disorder is a modification of the active site of both hexosaminidases. Here the substitution of an amino acid involved in the actual hydrolysis of N-acetylhexosamines seems to be implicated (Tallman et a/., 1973f ). 

Note.- There is another disorder with two defects the disorder of cationic distribution, which is found for binary compounds possessing two types of cationic sites. Such is the case, for example, in the spinel structure of Fe304, which has tetrahedral cationic sites and octahedral cationic sites, between which the Fe and Fe ions are distributed. This disorder is dealt with in the same way as the anti-structure... 

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