Читать книгу All sciences. №5, 2023. International Scientific Journal - Ibratjon Xatamovich Aliyev - Страница 5

UDC 548.1.024.5

Karimov Boxodir Xoshimovich

Candidate of Physical and Mathematical Sciences, Associate Professor of the Department of "Technological Education" of the Faculty of Physics and Technology of Fergana State University

Ferghana State University, Ferghana, Uzbekistan

Annotation. The anomalous photovoltaic effect observed earlier for LibO 3:Fes ferroelectrics is a special case of a more general FE existing in crystals without a center of symmetry and described by the third ai j k tensors.

Keywords: photovoltaic effect, ferroelectrics, tensor, tensor components.

Аннотация. Аномальный фотовольтаический эффект, наблюдавшийся ранее для сегнетоэлектриков Li bO3:Fe SbSJ, является частным случаем более общего ФЭ существующего в кристаллах без центра симметрии и описываемого тензорам третьего a_{i j k}.

Ключевые слова: фотовольтаический эффект, сегнетоэлектрики, тензор, компоненты тензора.

The components of the aij tensor are nonzero for 20 acentric point symmetry groups. With uniform illumination by linearly polarized light of a homogeneous piezo crystal and ferroelectrics, a photovoltaic current arises in it. The sign and magnitude of the photovoltaic current depends on the orientation of the polarization vector of light with its components and Ul*, the direction of its propagation and the symmetry of the crystal.

In accordance with (I) and the symmetry of the point group, it is possible to write an expression for the photovoltaic current. Comparison of the experimental criminal dependence with (β) makes it possible to determine the photovoltaic tensor aajk or photovoltaic coefficients

(a* is the light absorption coefficient).

If the electrodes of the crystal are opened, the photovoltaic current generates a photovoltaic voltage of 103-105 B. the value of which can be several orders of magnitude greater than the band gap of piezo or ferroelectrics. There is no FE in centrosymmetric crystals.

We studied a-quartz, one of the more common crystalline forms of silica (SiO2). At tempratures up to 573o, there is a so-called "low-temperature" a-quartz. A-quartz crystals belong to the trigonal trapezohedral class of the trigonal system (point group of symmetry 32) and are often found in two known forms: right and left crystals. At normal pressure and temperature of 573o With a – quartz turns into a hexagonal—trapezohedral class of the hexagonal system (point symmetry group 622).

The third—order axis in quartz is the optical axis of the crystal. One of the axes of the second order is the electric axis and the normal to both of these axes is the mechanical axis.

The symmetry of the quartz structure determines the symmetry of the properties of this crystal.

Quartz has the need to rotate the plane of the field, not only along the optical axis, but also in a direction perpendicular to it. It has been experimentally established that the ratio remains constant for wavelengths from 545 to 565 Nm and is equal to 054, i.e. the rotation of the plane in the directions perpendicular to the optical wasp is immeasurably two times less than that of the optical wasp. Despite all the "popularity" of quartz, both its properties have not yet been studied in detail.

In this paper, the results are presented, the effect of the polarization of light on

Af effect in natural crystal -quartz with natural coloring.

Figure 1 shows the angular instability of the photovoltaic current in a native a-quartz crystal with a natural color. The crystals were suspended in the impurity spectral region (l- 300—500 nm, a2 = 2cm -1) at room temperature. Figure 1 shows two orientational angular dependence Jx (b) when illuminated in the direction of the a-z axis, while for a-quartz K11 = (1—3). 10—13 A. cm (W) -1.

The illumination in the Z—direction reveals a noticeable deviation of Jx(b) from the theory. Perhaps this is due to the difference in the values of the optical activity coefficient of quartz for the Z— and Y—directions. Attention is drawn to the very low value of the photovoltaic coefficient K11 in a-quartz. It characterizes the impurity centers responsible for the natural coloring of natural crystals and does not reflect the asymmetry of their own transitions. Unfortunately, a-quartz impurity centers have not been specifically investigated; this provides an independent task.

The field was measured by the compensation method

the corresponding photo voltage V=El generated in quartz in the x-axis direction. At room temperature, the following values were obtained:

Due to the temperature dependence of the conductivity of quartz, the field and the photon voltage M increase with decreasing temperature.

Literature

1. Ryvkin S. M. Photoelectric phenomena in semiconductors Fizmatgiz.1963,494p

.2. Fridkin V. M. Ferroelectrics-semiconductors. M., Nauka 1976.