Interstitial oxygen atoms

Assume that the iron atoms in the crystal are in a perfect array, identical to the metal atoms in the sodium chloride structure, and that the 0.058 excess of oxygen is due to interstitial oxygen atoms being present, over and above those on the normal anion positions. The unit cell of the structure now contains 4 Fe and (4 x 1.058) O. The density is calculated to be 6076 kg m-3. 

If the interstitial oxygen atoms are transformed to oxide ions, electrons must be provided, generating two holes ... 

The closely related phase La2Cu04 (Section 4.3.3) is similar. In both of these materials there is strong evidence to suggest that the interstitial oxygen atoms are not distributed at random but are partly or completely ordered, depending upon preparation conditions. This has significance for high-temperature superconductors (Section 8.6). 

Figure 5.16 Willis clusters in UOj+y Open circles, oxygens small filled circles, uranium atoms in the UO2 structure. A 2 2 2 defect cluster consists of two interstitial oxygen atoms (large filled circles) and two normal oxygen atoms displaced from their ideal positions (open squares) to new interstitial positions (hatched circles). A 2 1 2 defect cluster would consist of one interstitial oxygen and two normal oxygens displaced from their ideal positions. (After Anderson, 19726.)...

O dimers may appropriately be called peroxy anions, 022 . In a silicate matrix they appear to occur as peroxy links or, more generally, peroxy entities, X/00 Y where X,Y = Si4+,A13+, Fe3+... Chemically a peroxy entity represents an extra oxygen it may be called an interstitial oxygen atom though this does not correctly convey the covalent binding in the 0-0 bond. 

The MX2+X phases contain interstitial anions. As with the anion-deficient phases, these interstitials are not random point defects, but ordered or clustered. The earliest cluster geometry to be postulated was the [2 2 2] cluster in UO2+J, the prototype anion-excess flnorite phase. The cluster is composed of 2 interstitial oxygen atoms displaced along (110), two interstitial oxygen atoms displaced along (111) in UO2+J (Figure 5). Other cluster geometries have also been proposed in this oxide, and the defect structure of this well studied phase is still not completely resolved. 

For the stoichiometry U02.25, the structure can be simplified to an arrangement of4 3 2 clusters [25].These clusters are composed of four interstitial oxygen atoms in the (110) direction with three oxygen vacancies and two interstitial oxygen atoms in the (111) direction. The addition of this oxygen causes the expansion of the cubic structure so that the cell dimension for U4O9 is approximately four times that of UO2 [6], although the cubic structure is retained. 

Figure 7. Reproducibility of consecutive measurements of the same spot on a Czochralskl silicon wafer containing approximately 7.3 X 10l7 Interstitial oxygen atoms/cm. ...

It is proposed that intrinsic Frenkel disorder adds to the interstitial oxygen atoms resulting from the variation of oxygen pressure. From these assumptions, the diffusion coefficient in region I may be written... 

Table VII lists the mole fraction of extrinsic defects at 831°C calculated from (16) at the pressures listed. The tensimetric data yield information only on the extrinsic defects. To this calculated number a value has been added which is interpreted to be the mole fraction of interstitial oxygen atoms due to the Frenkel equilibrium...

Kajihara, K., Skuja, L., Hirano, M., and Hosono, H., Role of mobile interstitial oxygen atoms in defect processes in oxides Interconversion between oxygen-associated defects in SiO, glass, Phys. Rev. Lett. 92, 015504 (2004). 

Positions in a crystal not normally occupied by an atom, called interstitial positions, are denoted by the subscript i. For example, O. would represent an interstitial oxygen atom in La CuO. ... 

Chen T, Liu TY, Zhang QR, Li FF, Yi ZJ, Tian DS, Zhang XY (2007) First-principles smdy of PbW04 crystal with interstitial oxygen atoms. Phys Status Solid A 204 776... 

The structures of the alkali metal suboxides have been discussed in terms of bare metal clusters stabilized by interstitial oxygen atoms. Due to the direct M-M bonding between the clusters, the suboxides are metallic and show electrical properties [220] which are similar to the free alkali metals. 

Calculations on interstitial oxygen atoms Oj in MgO crystal are of interest because of the possibility of their formation as a primary product during radiation damage. 

In metal oxides with excess oxygen the predominating point defects are interstitial oxygen atoms or ions. The formation of a neutral interstitial oxygen atom through reaction of oxygen with the oxide is written... 

No new lattice sites are formed in this reaction. The neutral interstitial oxygen atoms may in principle be ionised to yield electron holes and interstitial oxygen ions with negative effective charges, so that the total reaction becomes, for instance,... 

The defect equilibria involving the formation of interstitial oxygen atoms or ions in oxides with excess oxygen may be set up following the same treatment as applied to the other defects which have been dealt with above. The concentration of interstitial oxygen species increases with, and the formation of charged oxygen interstitials is accompanied by the formation of electron holes. 

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