The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
COMPUTER MODELLING OF NANOPARTICLE DEFECTS IN IMPURED
KBR CRYSTALS
A. DAULETBEKOVA. A . AKILBEKOV, A. VASIL’EVA, M. ZDOROVETS L.N. Gumilyov Eurasian National University, 5 Munaitpasov st. Astana, Kazakhstan, e-mail: alma_dauletbek@mail.ru
The irradiation o f metals, semiconductors, or isolators leads to the formation o f Frenkel defects such as a vacancy and an interstitial. In the alkali-haloid crystals the basic Frenkel defects are F- and H- centers, which represent an anion vacancy with a trapped electron and the haloid interstitial like 0 ~ quasi-molecule with the one of the nearest anions, and also a and I - pairs, which represent an anion vacancy with a haloid interstitial.
The main way to radiation defects formation is an electron excitation decay. At temperatures above 20-30 K the interstitials become shiftable and make the thermoactivated jumps; as a result o f the diffusive moving they annihilate with the anion vacancies or are captured by impurities or make some aggregates. Also it is possible the process of tunnelling charge modification from neutral Frenkel pairs into charged pairs occurs.
During the irradiation process the number of defects grows due to the aggregation process. At temperatures 80-200 K di-H-centers (historically called V4-, V2-centers) dominate, which can get two anionic and one cationic set forming the X 3~ - molecule. In this case it is necessary if the cationic
Section IV. Application O f Nuclear Technologies In Industry, Medicine And Agriculture
The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
Frenkel defects would be created. Interstitial cation and anion migrate generating the dislocation loops. The more complicated aggregates form at a higher temperature; a halogenoccupied an anion cation set forms (X2)m cluster or
x~
-molecule to be connected to the nearest halogen ion (m, n is a number of forming units). Aggregated defects are the nanoparticle defects. A lot of researches are dedicated to the investigations of microstructure of X 3~ -molecular defects and di-H-centers. The structure of complex aggregates and impurity influence is steel the poorly studied problem. In our research it is considered the computer models of different aggregate centers and compared them with experimental data.The modeling of aggregate centers in KBr crystals have been performed with the help of the software for quantum and chemical calculation such as CAChe WS Pro 6.1.12 (license Ne 1503000353) using the PM3 parametrizable method. There were several models to considerate: the crystal lattice 3x3x3 from 27 ions, the second model by size o f 5x5x5 from 125 ions, and also the case was considered when each ion could be relaxed or fixed. The absorption spectrum of free (Br3-) molecules was calculated to compare it with the similar absorption spectra of the molecules in water solutions. The maximums of absorption bands for 4.6 eV (Br3-) were in a good agreement with the calculated values. The absorption spectra of the molecules were computes also in the KBr crystal lattice, where the geometrical size of the defect gave good results for the model of Y4-center. Then the more complex aggregates were investigated and also the Li and Na cation- homologs impurity influence were considered.
