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STRUCTURE OF SOLID SOLUTIONS BASED ON Bi2BVI3 AND Sb2BVI3 (BV1 -
Se, Те)
Xolmatova Ruxshona Musinjon qizi
Fergana State University, 3rd year student of Physics
ABSTRACT
This article presents the crystal lattice structure of Вi2ВVIз and БЬ2Вп3 (Вп - Бе,
Те) solid alloys, changes in their parameters under a certain temperature.
Key words: solid alloy, solid solution, stoichiometric composition, crystal lattice, crystal lattice parameters
АННОТАЦИЯ
В статье представлена структура кристаллической решетки твердых сплавов Вi2ВVIз и БЬ2Впз (Вп - Бе, Те) изменение их параметров при определенной температуре.
Ключевые слова: твердый сплав, твердый раствор, стехиометрический состав, кристаллическая решетка, параметры кристаллической решетки.
ANNOTATSIYA
Ushbu maqolada В12В^1з va БЬ2Вп3 (Вп - Sе, Те) qattiq qotishmalarning kristall panjara tuzilishi, ma'lum harorat ostida ularning parametrlari o'zgarishlari keltirilgan.
Kalit so 'zlar: qattiq qotishma, qattiq eritma, stexiometrik tarkib, kristall panjara, kristall panjara parametrlari.
One of the pressing issues in the world is the implementation of the mutual conversion of heat and electricity through thermoelectric materials with high efficiency without harming the atmosphere in obtaining environmentally friendly electricity. Ushbu Вi2ВVIз va Sb^3 ffi71 - Sе, Те) Among the chalcogenides that are components of solid solutions based on Вi2ВVI3 and Sb^^ (ВV1 - Sе, Те) bismuth telluride has been studied in the most detail. Thermoelectric materials based on bismuth antimony telluride and selenide with high thermoelectric properties and characteristics are important in creating thermoelectric devices. Such thermoelectric materials are widely used in generators, refrigerators, thermostats, air conditioners and other devices to convert heat energy directly into electricity. Therefore, solid solutions based on bismuth telluride (Bi2Te3) have the best thermoelectric properties in the temperature range of 200-600 K.
Bi2Te3 forms continuous isomorphous solid solutions with Bi2Se3 and Sb2Te3. A number of conditions must be met for this:
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1) initial compounds must belong to the same symmetry class and have lattices with similar parameters;
2) atoms replacing each other should not differ greatly in size and be similar in chemical properties.
All these conditions are well fulfilled for Bi2Te3 Bi2Se3 and Sb2Te3 (Table 1). Table 1. Space group and lattice parameters of Bi2Te3, Sb2Te3 and Bi2Se3 at T= 300 K
Compound Lattice Space group parameters, Â
Bi2Te3 [35] D53d (Rim) 4,3835 30,487
Sb2Te3 [51] D53d Rm) 4,275 30,490
Bi2Se3 [50] D53d (Rim) 4,134 28,546
Covalent radii for Se, Bi, Te and Sb are respectively: 1.17; 1.51; 1.37 and 1.41 A. In Bi2Te3 - Sb2Te3 solid solutions, Bi sites are replaced by Sb atoms.
Te(1) - Sb - Te(2) - Bi - Te(1) In Bi2Te3 - Bi2Se3, the Se atom is primarily located in Te(1) and Te(2) and forms the following chains:
- Te(1) -Bi-Se-Bi- Te(1) -Or -Se-Bi- Te(2) -Bi- Te(1) -.
Lattice parameters of Bi2Te3 - Sb2Te3 and Bi2Te3 - Bi2Se3 - were measured in [42, 46, 48, 50]. Data for the first solid solution are shown in Figure 1, and for the second - in Figure 2. The parameter a obeys Wegart's rule in both cases.
Figure 1. Variation of a, c parameters depending on the composition of the Bi2Te3 - Sb2Te3 solid solution system.
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Figure 2. Dependence of parameters a and c on composition in Bi2Te3 - Bi2Se3 solid solution: 1 - hardened samples; 2, 3 - single crystals grown at a speed of 1.2 and 0.2 mm/h, respectively.
It decreases when going from Bi2Te3 to Sb2Te3 and Bi2Se3, mainly because the substituent atoms (Se and Sb) are smaller compared to the matrix atoms (Te and Bi).
The c parameter changes in a more complex way depending on the composition of the solid solution. So, for example, in Bi2Te3 - Bi2Se3, c decreases linearly only up to 30 mol% Bi2Se3, after which a deviation from Wegart's law is observed (Fig. 3). In this solution, Se replaces Te(2) until the composition Bi2Te2Se, and only then
Te(l).
Bi2Se3
20 40 60 60 100 Bl2Tei Bl2s tyMOA% Bl2Sei
Figure 1.9. Deviation from Vegart's law for parameter c in Bi2Te3 solid solution: 1 - data obtained from work; 2 - [48].
A deviation from Vegart's law in parameter c is observed near Bi2Te2Se. This may be due to changes in van der Waals interactions between individual quintets. It is known that such an interaction is stronger between identical systems (Te(1) - Te(1)) or Se - Se) than between dissimilar systems (Te(1) - Se) is stronger. If this assumption is correct, the maximum deviation from Wegart's law should be for a Bi2Se3 composition of 67 mol%, which corresponds to a 50% to 50% mixture of Te and Se atoms in the Te(1) layers. will come. This is well confirmed by experience (see Figure 1.9).
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