​Radiation Effects in Sapphire Crystals

Radiation Effects in Sapphire Crystals

In the field of modern technological equipment, structural elements made of sapphire are used under extreme conditions (high temperatures, high mechanical loads and high radiation doses). For example, in spacecraft, nuclear reactors and thermonuclear units, the sapphire crystal structure is at the atomic level Changes in the material's physical properties, such as conductance, strength, and size, may change significantly if the radiation-induced defects (RDs) are large in number. . Some of the changes are somewhat unusual in character. RDs differ from those created by crystal growth and subsequent mechanical and thermal processing defects. Some radiation formations (such as superlattices of vacant holes) are not obtained by other methods.

Those high-energy particles that participate in elastic and inelastic interactions with the target nucleon lead to the displacement of lattice atoms. In low-energy bombarding ions, this displacement leads to the formation of single vacancies and single interstitial atoms. When the lattice is given to the lattice by the bombarding ions When the energy of the atom is above a certain threshold, the above-mentioned defect pairs are formed. When the energy exceeds the threshold migration energy by a large amount, a displacement flow is formed. In the path of the movement of the displacement flow, individual vacancies and interstitial atoms are generated, already their complexes. Then, in the process of establishing thermal equilibrium between the region adjacent to the heated cathode and the rest of the crystal, these defects undergo structural reconstruction induced by diffusion mechanisms. When a vacancy encounters an interstitial atom, some of them are lost due to the disappearance of the Frenkel pair. disappears. Other defects change in their size, shape and position. Therefore, the interstitial atomic group transforms into an interstitial dislocation ring. The vacancy group may develop in two directions depending on temperature, crystal structure type and other factors. One is the formation of vacancy-type dislocation loops, which is a type of hole in the crystallographic plane. The other is the formation of vacancy holes of different sizes. Small vacancy holes have a facet shape corresponding to the parent crystal type; Large vacant holes have a circular hollow shape.

In addition to the defects caused by nucleon reactions between bombarding particles and crystal atoms, different types appear, these variants are distributed as impurities in the matrix of the material. These are noble gases such as helium, krypton and xenon. In addition, other exotic Cells are also formed in the irradiated material. These impurity-induced defects may be maintained at lattice sites (substitutional impurities) or reach interstitial spaces (interstitial impurities). When migrating in the crystal during diffusion, impurity-induced defects The defects (especially the highly mobile noble gases) interact with the defects of the crystal itself, so a mixed-type defect group is formed. These impurity-type defects gather at grain boundaries, dislocations or other large defects and form and can slowly transform Agglomerates form a second phase. When interacting with vacant pores, gaseous impurities may accumulate in the pores. These induced irradiation defects may bring about changes in the strength characteristics of the material (e.g. shear stress, flow stress, limit strength and hardness).

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