I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials of Kola Scientific Center of Russian Academy of Sciences, Apatity, Russia:

V. M. Voskresenskiy, Post-Graduate Student

O. R. Starodub, Researcher, e-mail: starodub@chemy.kolasc.net.ru
N. V. Sidorov, Divisional Manager
M. N. Palatnikov, Divisional Manager
V. T. Kalinnikov, Director

In the present work the phenomenon of streamlining of structural distortions oxygen-octahedral clusters of lithium niobate crystal within the limits of semiclassical atomistic model was studied. Computer modeling of the processes occurring at formation energetically equilibrium oxygen-octahedral clusters in in the ferroelectric phase of lithium niobate single crystal (LiNbO₃) depending on the size of clusters is executed. The complex of programs created by us which has allowed to minimize energy of clusters at the expense of movement or removal of “critical” atoms, that is atoms at which the total energy is positive has been for this purpose used. The received results have been compared with the data of vacancy models of streamlining of structural units cationic sublattice lithium niobate. It was shown that the best ordering is characteristic of the structures built along the crystallographic y axis, where the structure is well described vacancy model (М5/2) with any an arrangement of superfluous ions Nb⁵⁺ in positions Li⁺ and in vacant next octahedrons appears the most ordered. The least ordered ones are those built along the polar z axis. In a direction of axis z the greatest disorder in size of relation R = Li/Nb is observed. The structure of clusters stretched along the crystallographic axis x is successively described by different types of vacancy models depending on the size of the cluster. Attempt visually is undertaken to present the processes occurring at formation of energetically equilibrium crystal of niobate of lithium. The qualitative sight at problems formation of defects of lithium niobate single crystal was a work problem not quantitative, namely so that it was possible to present processes of change of position of atoms at increase in the sizes of cluster in a crystal.

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