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DIFFUSE α-β PHASE TRANSITION IN THE SURFACE LAYERS OF QUARTZтезисы доклада
- Авторы: Vettegren V.I., Mamalimov R.I., Sobolev G.A., Ponomarev A.V., Kulik V.B.
- Сборник: Book of abstracts, INTERNATIONAL CONFERENCE "MECHANISMS AND NON-LINEAR PROBLEMS OF NUCLEATION AND GROWTH OF CRYSTALS AND THIN FILMS"
- Тезисы
- Год издания: 2019
- Место издания: SAINT-PETERSBURG, RUSSIA
- Первая страница: 212
- Последняя страница: 212
- Аннотация: The temperature dependence of the α-phase concentration in surface layers of solution-grown and nature quartz single crystals has been studied in the range 290–820 K using IR and Raman spectroscopy. It has been found that, in the surface layer ∼0.15 μm thick and in the volume of crystals,the concentration of the α-phase behaves with increasing temperature as expected for a first-order phase transition, namely, before 800 K, it remains constant, and it tends to zero at T → 846 K. At a distance from ∼1 to 20 μm from the surface, however, the concentration of the α-phase starts to decrease already at ∼350 K, while at 812 K it decreases to one-fifth of the original value. This is paralleled by the increase of the concentration of the β-phase. The diffusive of the α-β phase transition is initiated by distortion of the quartz crystal lattice around growth dislocations. The volume of β-phase is the greater than α-phase. That is why appearing of β-phase leads to internal stresses. It has been established that at distances up to ∼1 μm from the surface, tensile stresses appear at 400 K reaching ∼ 300–400 MPa. At the same time, compressive stresses develop in a layer ∼1 to 20 μm thick at a temperature above 500 K, and reach a maximum at ∼650 K. This effect caused by “unfreezing” transverse vibrations of growth dislocations. Because of this the single crystal is split into nanocrystals with linear sizes from ~8 to ~28 nm in this layer. The nanocrystals are again transformed into a single crystal at a temperature above 650 K and compressive stresses begin decreases. The temperature dependence of the concentration of α-phase is changed in the surface layer of a natural crystal under influence of water. Concentration of the α-phase decreases by about one half in the layer at a depth of ~6 μm at ~370 and ~570 K. The revealed behavior of the α-phase concentration with the increase in the temperature has been assigned to the influence of water on crystal lattice distortions near growth dislocations. It has been found that tensile stresses generated with increasing temperature in a near surface quartz layer to ~0.8 μm thick can reach ~170 MPa at 780 K. The onset of such stresses brings about destruction of surface layers of quartz.
- Добавил в систему: Пономарев Александр Вениаминович