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Phase transitions
Diffuse phase transition in a surface quartz layer with variations in temperature
V. I. Vettegrena,
R. I. Mamalimova,
G. A. Sobolevb a Ioffe Institute, St. Petersburg
b Institute of Physics of the Earth, Russian Academy of Scienses
Abstract:
The temperature dependence of the
$\alpha$-phase concentration in surface layers of a solution-grown quartz crystal has been studied in the range 290–820 K. This has been achieved by measuring the intensity of the 695.1, 785.0, and 1061.5 cm
$^{-1}$ bands in the
$\varepsilon''(\nu)$ IR damping spectra. It has been found that, in a surface layer
$\sim$0.15
$\mu$m thick, the concentration of the
$\alpha$-phase behaves with increasing temperature as expected for a first-order phase transition, namely, before 800 K, it remains constant, after which at
$T\to$ 846 K, tends to zero. At a distance from
$\sim$1 to 20
$\mu$m from the surface, however, the concentration of the
$\alpha$-phase starts to decrease already at
$\sim$350 K, while at 812 K it decreases to one-fifth of the original value. This is paralleled by an increase in the intensity of the 804 cm
$^{-1}$ band assigned to the
$\beta$-phase. The diffusive pattern of the
$\alpha$–
$\beta$ phase transition is initiated by distortion of the quartz crystal lattice around growth dislocations. The internal stresses arising in these layers have been estimated from the shift of the band maxima. It has been established that at distances up to
$\sim$1
$\mu$m from the surface, tensile stresses reaching
$\sim$300–400 MPa appear at 400 K. These stresses drive in the surface layer of the macrocrystal microcracks culminating in total destruction of the sample. The appearance of tensile stresses is assigned to an increase in volume of the macrocrystal layer located at a distance from
$\sim$1 to 20
$\mu$m from the surface and the growth in it of the
$\beta$-phase concentration. At the same time, compressive stresses develop in a layer
$\sim$1 to 20
$\mu$m thick at a temperature above 500 K, which reach a maximum at
$\sim$650 K, to fall off thereafter with increasing temperature. The compression is caused by vibrations of growth dislocation loops in the temperature range specified.
Received: 02.04.2013
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