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3FORMATION OF PHASES IN COMPLEX OXIDES WITH A PYROCHLORE STRUCTURE CONTAINING LITHIUM IONS Kh.N. Bozorov
Namangan Engineering and Technology Institute Corresponding author. E-mail: [email protected] https://doi.org/10.5281/zenodo.10181851
Abstract: Formation laws of potassium and lithium antimonate-tungstates during heating of complex oxide (y-x)K2CO3-xLi2CO3-ySb2O3-2(2-y)WO3 mixture in air were studied. For a temperature of 1123 K in the KSbO3-WO3-LiSbO3 concentration triangle, the formation zone of LixKy-xSbyW2-yO6 containing phases with a pyrochlore-type structure was determined.
Keywords: ionic conductivity, pyrochlore-type structure, potassium antimonate tungstate, concentration triangle.
ОБРАЗОВАНИЕ ФАЗ В СЛОЖНЫХ ОКСИДАХ СО СТРУКТУРОЙ ПИРОХЛОРА, СОДЕРЖАЩИХ ИОНЫ ЛИТИЯ
Аннотация: Изучены закономерности образования антимонатов-вольфраматов калия и лития при нагревании смеси сложных оксидов (y-x)K2CO3-xLi2CO3-ySb2O3-2(2-y)WO3 на воздухе. Для температуры 1123 К в концентрационном треугольнике KSbO3-WO3-LiSbO3 определена зона образования LixKy-xSbyW2-yO6, содержащих фазы со структурой типа пирохлора.
Ключевые слова: ионная проводимость, структура типа пирохлора, вольфрамат антимоната калия, концентрационный треугольник.
INTRODUCTION
The studied solid electrolytes have ionic conductivity at the level of the world's best analogues, which allows them to be recommended for use in the following various electrochemical devices: chemical sources of electricity, thermoelectric generators; ion and ion-plasma engines for space objects; sensor devices for determining the activity of alkali metals in various liquid and gaseous media as diaphragms to separate the anode and cathode spaces during the electrolysis of molten salts [1-6]. A type of synthesized solid electrolytes with high conductivity for this type of ions, but different chemical composition; also differ in the type and concentration of modifying inputs, allowing to choose the electrolyte with the most appropriate performance indicators for working in certain conditions. Another area of application of the synthesized solid electrolytes is for research purposes, such as studying the thermodynamics of solid-phase reactions. The phase relations in the considered quasibinary systems can be used as information about the values of electrical conductivity depending on the temperature and composition of solid electrolytes, as well as the results of the study of the crystal structure of the main compounds [1- 8].
Compounds based on complex antimony oxides of the pyrochlore type are of great interest because they are good ion conductors and ion exchangers [1-2]. These compounds can be obtained by solid phase synthesis in the (y-x) K2CO3-xLi2CO3-ySb2O3-2 (2-y) WO3 system [3-4]. Carriers involved in ion transfer and ion exchange are usually alkali metal ions. In this case, such ions can be potassium and lithium ions. The replacement of potassium ions with a large radius by lithium ions with a smaller ionic radius indicates that such compounds have large values of ionic conductivity, when changing the amount of antimony (V) and tungsten (VI) ions in the 16c positions of the pyrochlore-type structure, it is possible to obtain a wide range of compounds with an irregular cation sublattice [8-12].
However, until now, the issues of formation and stability of the phases obtained in this system have not been studied, and the concentration field of the synthesis of pyrochlore-type phases has not been determined.
In this regard, the purpose of this work was to establish the field of formation of potassium and lithium antimonate tungstate in the (y-x) K2CO3-xLi2CO3-ySb2O3-2 (2-y) WO3 system, and to determine the composition and structure of the resulting phases.
EXPERIMENTAL
Powdered antimony Sb (III) oxide, W (VI) tungsten, "chemically pure" potassium and lithium carbonates were taken as initial reagents. Reagents were pre-ground, homogenized and dehydrated. The mixtures were prepared in the range of 0 <x <y, 1.0 <y <2.0 in the amount of (y-x) K2CO3-xLi2CO3-ySb2O3-2 (2-y) WO3 moles. The samples were heated in air at a temperature of 1123 K for a long time until a constant mass was formed. As a result of solid-phase synthesis, it was assumed that complete decomposition of potassium and lithium carbonates and oxidation of trivalent antimony to the pentavalent state occurs.
The phase composition was investigated using X-ray analysis method performed on a D8 ADVANCE diffractometer (Bruker, Germany) under filtered CuKa1 radiation. The parameter a of the elementary cell was determined by reflexion 8.4.4. The error in determining the a parameter was ± 0.005 Â [8-10].
X-ray data shows that at 1123 K, the single-phase zone of pyrochlore-type compounds is bounded by a pentagon, the ends of which correspond to points 1-5 on the KSbO3-WO3-LiSbO3 diagram (Fig. 1). Outside this region, individual compounds with other types of symmetry can be formed during isothermal heating of mixtures, depending on the specific values of x and y.
RESULTS AND DISCUSSION
X-ray patterns of single-phase samples of potassium and lithium antimonate tungstates have the same set of diffraction maxima, the sum of which is described by the quadratic formula for cubic syngony crystals and satisfies the extinction laws of the spatial symmetry group Fd-3m. Let's move on to the analysis of the composition of potassium and lithium antimonate tungstates located at the boundaries of the defined concentration area (Fig. 1). In the segment connecting points 1, 2, there are potassium antimonate tungstates in KySbyW2-yO6 (1.0<y<1.375). Thus, the KSbWO6 composition phase obtained by solid-phase synthesis is known in the literature and has a pyrochlore-type structure (point 1 in the diagram). With an increase in the concentration of potassium ions in the system, the composition of the phase changes, and at y = 1.375 it is described by the chemical formula K1.375W0.625Sb1.375O6 (point 2 in the diagram).
X-ray images of the obtained samples contain a certain set of diffraction maxima in the region 1.0<y<1.375, which are satisfactorily described for cubic syngonia crystals and the analysis of the extinction laws of reflexes shows that the composition of KySbyW2-yO6 was formed in the area with the pyrochlore-type structure of the spatial symmetry group Fd-3m [10-12].
Redistribution of the intensity of reflexes with even and odd index is noted on the X - ray graphs of the samples placed in the field (1.0<y<1.375) (Fig. 2 a,b,c,d). In particular, the intensity of the (311) reflex decreases monotonically with increasing y compared to the (222) reflex (Fig. 3, a). At the same time, the unit cell parameter a increases from 10.235 Â to 10.322 Â (Fig. 3b). It can be seen that the change of structural parameters in the phase of KySbyW2-yO6 composition is related to the filling of appropriate positions of the pyrochlore-type structure with ions.
As the amount of Sb2O3 decreases, the x-concentration of lithium ions increases in the samples placed in the concentration interval (0<x<1.375) between (points 2 and 3) va a sphere
containing LixKi.375-xSbi.375Wo.625O6 is formed. The sample containing Lii.375Wo.625Sbi.375O6 (point 3) contains the maximum concentration of lithium ions. An increase in the amount of WO3 in the LixKy-xSbyW2-yO6 system leads to a change in composition to Li1.25W0.75Sb1.25O6 (point 4). Phase 3-4 is stable (Fig. 1).
As the amount of WO3 increases, the stability of the phase with sodium ions decreases in the range of 4-5 (Fig. 1) and until lithium ions are completely replaced by potassium ions (point 5), a Lio.4Ko.6SbWO6 compound with a stable pyrochlore-type structure is formed [13-15].
For samples with LixK1.375-xWo.625Sb1.375O6 and LixK1.25-xW0.75Sb1.25O6 contents, it was found that the dependence of the unit cell parameter on a (Fig. 4, a, b) is non-monotonic and is characterized by two concentration areas. As the amount of lithium ions increases in the first area, the value of a decreases monotonically, this is due to the fact that potassium ions have a smaller radius (r(K+)=o,133 nm, r(Li+)=o,o68 nm) than lithium ions [16-22]. In this case, the relative intensity of reflexes located in this concentration area does not undergo significant changes (Fig. 5, a, b). In the second area (0.6<x<1.2), a monotonous increase of the parameter a of the elementary cell is observed, redistribution of reflex intensity with even and odd index is noted (Fig. 5, a, b). The decrease in the reflex intensity with odd indices and the increase in the unit cell parameter are apparently due to the filling of the appropriate positions of the pyrochlore-type structure with ions.
CONCLUSIONS
The properties of pyrochlore-type structural phases in the (y-x)K2CO3-xLi2CO3-ySb2O3-2(2-y)WO3 system when heated at a temperature of 1123 K in the KSbO3-WO3-LiSbO3 concentration triangle were studied.
When heated in air, a complex oxide (y-x)K2CO3-xLi2CO3-ySb2O3-2(2-y)WO3 phase of potassium and lithium antimonate-tungstate is formed. In the KSbO3-WO3-LiSbO3 concentration triangle, the LixKy-xSbyW2-yO6 phase with a pyrochlore type structure was formed for a temperature of 1123 K.
The obtained results make an important contribution to the understanding of the mechanism of ion transport in complex oxide compounds with pyrochlore-type structure.
In our future work, we hope to expand the concentration ranges of potassium antimony tungstate, achieve high levels of ionic conductivity in them, and contribute to the creation of new alternative energy sources.
LiSbO3
Fig. 1. In theKSbO3-WO3-LiSbO3 composition diagram, the area wherepyrochlore-type potassium and lithium antimonate tungstates are formed
(T = 1123 K)
Fig.2. Diffractograms of samples obtained after heating at 1123 K and having gross compositions: KWSbO6 (a), K1.125W(J.875Sb1.125O6 (b), K1.25W0.75Sb1.25O6 (c), K1.375W(J.625Sb1.375O6
(d).
Fig.3. Variation of the relative intensity of the reflex J311/J222 (a) and unit cell parametric a (b) as a function of the number ofpotassium ions in the KySbyW2-yO6
1.0<y<1.375 phase.
Fig.4. Dependence of the unit cell parameter a on the amount of lithium ions for LixKi.375-xWo.625Sbi.375O6 (a) andLixK1.25-xW0.75Sb1.25O6 (b) compositions.
Fig.5. Variation of the relative intensity of the J(3ii/J(222) reflex for LixKi.375-xWo.625Sbi.375O6 (a) andLixK1.25-xW0.75Sb1.25O6 (b) compositions according to the
number of lithium ions.
References
1. D.G. Klestchov, V.A. Burmistrov, A.I. Sheinkman, R.N. Pletnev. Composition and structures of phases formed in the process of hydrated antimony pentaoxide thermolysis. J. Solid State Chem. 94 (1), 220-226 (1991).
2. Yu.A.Lupitskaya, V.A. Burmistrov. Ionic conductivity of potassium antimonatungstate upon heterovalent substitution of Sb5+ for W6+ and doping with sodium and lithium ions. J.Modern science: theory and practice. (1), 46-49. (2010).
3. P.J.Baymatov, A.G.Gulyamov, B.T.Abdulazizov, Kh.Yu.Mavlyanov, M.Tokhirjonov. Features of the Chemical Potential of a Quasi-Two-Dimensional Electron Gas at Low Temperatures Features of the Chemical Potential of a Quasi-Two-Dimensional Electron Gas at Low Temperatures. International Journal of Modern Physics B. 2150070. 1-13. (2021), https://doi.org/10.1142/S0217979221500703.
4. E.I. Burmakin. Principles of Targeted Synthesis of Highly Conductive Solid Electrolytes Based on Complex Oxides. Tez. report VIAll-Union Conf. in electrochemistry. (3). 285 - 286. (1988).
5. G.Gulyamov, B.T.Abdulazizov, P.J.Baymatov. Three-band simulation of the g-factor of an electron in an InAs quantum well in strong magnetic fields. Journal of Nanomaterials, (2021). Article ID 5542559, https://doi.org/10.1155/2021/5542559.
6. A.I. Efimov and others. Properties of inorganic compounds: Handbook. L.: Chemistry. 392. (1983).
7. E. S. Sokolova, S. S. Sokolov and N. Studar. Chemical potential of the low-dimensional multisubband Fermi gas. J. Phys.: Condens. Matter 22, 465304 (2010). doi.org/10.1088/0953-8984/22/46/465304.
8. M. Avdeev, V.B. Nalbandyan, I.L. Shukaev. Alkali Metal Cation and Proton Conductors: Relationship between Composition, Crystal Structure and Properties. Solid State Electrochemistry I, Wiley-VCH, Weinheim. (7). 227-278. (2009).
9. T. Kudo, P.J. Gelling, and H.J.M. Bowmeester, [et al.]. Survey of Types of Solid Electrolytes. Solid State Electrochemistry. 201-228. (2006).
10. B.T. Abdulazizov. Cyclotron mass of an electron in strong magnetic fields in a wide InAs quantum well. Eurasian Journal of Physics and Functional Materials 2022, 6(1), 32-37, DOI: 10.32523/ejpfm.2022060103.
11. V.G. Trofimov, A.I. Sheinkman, L.M. Goldstein, G.V. Kleshchev. Ophazetypepyrochlorine in the Na-Sb-O system. Crystallography. (16). 438-440. (1971).
12. J. Lian, L. Wang, J. Chen, K. Sun, R.C. Ewing, J.M. Farmer, et al. The order-disorder transition in ion-irradiated pyrochlore. Acta Mater. (51). 1493-1502. (2003).
13. Yu. A. Lupitskaya, V.A. Sviridov, A.V. Cherednichenko, D.A. Kalganov. Ion-conducting materials based on complex antimony oxides. Sat. abstract report L PNPI School of Condensed Matter Physics. 118. (2016).
14. E.V. Suleimanov, N.G. Chernorukov, A.V. Golubev. Synthesis and study of new representatives of the structural type of defective pyrochlore. Journal inorganic chemistry. (49). 357-360. (2004).
15. Yu.A. Lupitskaya, V.A. Bumistrov The structure of the phases formed in the Me2CO3-Sb2O3-WO3 system upon heating (where Me=K, Na). Vestnik Chelyab. state university. (3). 39 - 43. (2008).
16. O. A. Firsova, Filonenko, Yu.A. Lupitskaya, Kh.N. Bozorov, A.V. Butakov. Ion-Exchange Properties of Solid Solutions Based on Hydrated Forms of Antimonate-Tungstates of Monovalent Metals. Butler messages. (62). 74. (2020).
17. Yu. A. Lupitskaya, V.A. Burmistrov. Phase formation in the K2CO3-Sb2O3-WO3 system upon heating. Journal inorganic chemistry. (56). 329-330. (2011).
18. Yu. A. Lupitskaya, V.A. Burmistrov. Structure of phases formed in the Me2CO3-Sb2O3-WO3 system upon heating (where Me = K, Na). Vestnik Chelyab. state university. (3). 39-43. (2008).
19. Yu. A. Lupitskaya. Investigation of a phase with a pyrochlore-type structure formed in the (y-x)K2CO3-xLi2CO3-ySb2O3-2(2-y)WO3 (0<x<y, 1.0 <y<1.375) system upon heating to create ion-conducting ceramics. Sat. abstract report VII All-Russian scientific. conf. Syktyvkar. 57. (2010).
20. Kh.N. Bozorov, Yu.A. Lupitskaya, N.Yu. Sharibaev, G.U. Abdullaeva. Synthesis of XK2CO3-xSb2O3-(2-x)WO3 (0<x<2.0) - complex oxide compounds and technology for their production. Scientific Bulletin of NamSU. (12). 98-101. (2021).
21. B. T. Abdulazizov, G. Gulyamov, P. J. Baymatov, Sh. T. Inoyatov, M. S. Tokhirjonov and Kh. N. Juraev. Peculiarities of the Temperature Dependence of the Chemical Potential of a Two-dimensional Electron Gas in Magnetic Field. SPIN 13, 2250002 (2022), DOI:10.1142/S2010324722500023.
22. N. F. Uvarov and V. V. Boldyrev, "Size effects in the chemistry of heterogeneous systems," Usp. Khim., (70), (2001). doi: 10.1070/rc2001v070n04abeh000638.
