Point defects recovery

Meyer, A. G. Nicht lineare Ausgleichung von Reaktionsverlaufen bci linearer Aufheizung. Vortrag im Mathematischen Institut der TU Clausthal, 17.12.1965. 124> Gevers, R I. Nihoul, and L. Stals On the Analysis of Experimental Data on Point Defect Recovery. Phys. Stat. Sol. 15, 701/723 (1966). 

Dick and Styrus [63] report real-time resistivity measurements on shoek-loaded silver foils. The inferred vaeaney eoneentration is 1.5 x 10 per atomie site for samples shoek loaded to 10 GPa. The eombined effect of point-defect generation and reeombination to form vaeaney clusters, for example, can be influential on pulse-duration effeets such reload, release, and recovery. This topie has not yet reeeived the degree of experimental study that it deserves. 

The measurement of the resistivity is, therefore, a direct indication of the presence and the amount of point defects. This method has yielded important results on metals and semiconductors. The majority of recovery curves (annealing of point defects created at liquid He temperature) derives from resistivity measurements which are not too difficult to perform over a wide temperature range. Another possibility for following the recovery of defects created at low temperatures is the measurement of the release of the energy stored in defects using calorimetric methods. 

These and numerous other experiments prove that in metals the implanted atoms change their position and their surroundings between liquid He temperature and RT and that a considerable reordering of the lattice takes place even at low temperatures. The low-temperature recovery of ion-bombarded compounds is unfortunately completely unknown. Very few experiments at liquid-N temperatures indicate a strong temperature dependence too. A recovery of the majority of the point defects and centers below RT was found experimentally only for ionic crystals irradiated with electrons ... 

Tuomisto F, Saarinen K, Look D C, Farlow G C, Introduction and recovery of point defects in electron-irradiated ZnO, Phys. Rev. B, 72, 085206-11, 2005. 

Mitchell states that dislocation dissociation is rare in oxides. The only two cases in which it has been clearly observed (AI2O3 and MgAl204,) involve dissociation by climb, rather than glide, in situations where the point defects are probably helping the dissociation process. Therefore, it is of interest to study such cases as additional examples in which climb is involved, as one of the mechanisms in the recovery process. Figure 3.71 illustrates dislocation dissociation by climb in MgO-3.5 AI2O3 spinel. 

The thermal conductivity of irradiated CVD SiC exhibits a linear temperature dependence until thermal recovery of the irradiation-produced defects occurs in the point-defect regime, which suggests that the small vacancies or vacancy complexes dominating... 

Recovery of point defects created at low temperature occurs by several intermediate stages, generally involving clusters, and has been studied by various techniques electrical resistivity, differential scanning calorimetry, transmission electron microscopy (when the size of defect clusters is larger than 2 nm), positron annihilation (the lifetime of a positron in a three-dimensional vacancy cluster increases with the size of the cluster and can reach 500 ps), and Huang X-ray scattering (it increases when interstitials cluster into dislocation loops). 

Recovery of Point Defects After Irradiation or Quench... 

In pure metals, the recovery of point defects created or retained at low temperature follows a general scheme, evidenced by the study of isochronous annealing of irradiated materials. This is because the mobility of interstitials is much higher than that of vacancies. Typically, in a metal such as copper, interstitials become mobile around 50-100K ( ==0.1 eV), and at 100 K have either recombined with vacancies, or clustered in small dislocation loops, or bound to impurities. Vacancies become mobile above =250K and form clusters that dissociate at high temperature ( = 500 K). 

I2, T2) attributed to positrons trapped at the crystalline-amorphous interface had T2 0.32 ns and h exhibited a precipitous decrease from about 58% to about 50% at the yield point, followed by recovery back to about 58%. This phenomenon interpreted as indicating interfacial loss of defects occurs during the initial deformation process and then some unknown recovery process takes place subsequently. 

It is interesting to note that each increase in temperature permits a little more of the damage to heal. This shows that there is a spectrum of different types of defects, some of which are more resistant to correction than others. We know that small traces of impurity atoms can have a significant influence on the rate of recovery. Some of the defects produced are so stable that one must heat the metals to temperatures nearly halfway to the melting point in order to remove them. 

---