1061 ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2020, Vol. 65, No. 7, pp. 1061–1068. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2020, published in Zhurnal Neorganicheskoi Khimii, 2020, Vol. 65, No. 7, pp. 974–981. Phase Equilibria Thermodynamic Analysis, and Electrical Properties of Samples in the System Li 2 O–B 2 O 3 –Yb 2 O 3 M. M. Asadov a, *, N. A. Akhmedova a , S. R. Mamedova a , and D. B. Tagiev a a Nagiev Institute of Catalysis and Inorganic Chemistry, Azerbaijan National Academy of Sciences, Baku, AZ1143 Azerbaijan *e-mail: mirasadov@gmail.com Received December 26, 2019; revised January 27, 2020; accepted February 27, 2020 Abstract—Samples in the Li 2 O–B 2 O 3 –Yb 2 O 3 system were synthesized and studied by differential thermal analysis, X-ray powder diffraction analysis, and thermodynamic analysis. Polythermal sections and an iso- thermal section of the phase diagram of this system were constructed. It was shown that the polythermal sec- tions Li 2 O ⋅ 3B 2 O 3 –Yb 2 O 3 ⋅ B 2 O 3 and Li 2 O ⋅ B 2 O 3 –Yb 2 O 3 ⋅ B 2 O 3 are non-quasi-binary, and Li 2 O ⋅ 2B 2 O 3 – Yb 2 O 3 ⋅ B 2 O 3 and Li 6 Yb(BO 3 ) 3 –YbBO 3 are quasi-binary. The isothermal section in the Li 2 O–B 2 O 3 –Yb 2 O 3 system at 25°C has 15 stable tie lines, which divide the system into 14 triangles of coexisting phases. The com- pounds 6Li 2 O ⋅ Yb 2 O 3 ⋅ 3B 2 O 3 and 3Li 2 O ⋅ 2Yb 2 O 3 ⋅ 3B 2 O 3 were synthesized, and their physicochemical prop- erties were studied. The temperature dependences of the electrical conductivity of polycrystalline samples in the Li 2 O–B 2 O 3 –Yb 2 O 3 system at direct current were investigated. The activation energies of the conduction of semiconducting samples were determined. It was observed that, with adding Yb 2 O 3 (x = 0–0.02), the elec- trical conductivity of samples of the composition (1 – x)Li 2 O ⋅ 3B 2 O 3 –x Yb 2 O 3 ⋅ B 2 O 3 decreases, and the acti- vation energy increases from 0.87 to 0.94 eV. Keywords: lithium borate oxides, ytterbium oxide, polythermal sections, isothermal section, electrical con- ductivity of polycrystalline samples DOI: 10.1134/S0036023620070013 INTRODUCTION Oxide multicomponent materials are used in vari- ous areas, in particular, for producing dielectric and semiconducting materials, lasers, solar (voltaic) cells, optical detectors, and waveguides. Multicomponent systems containing mobile lithium ions are used, e.g., in high energy density solid-state batteries [1–5]. On the other hand, borate oxides are the best glass formers [6]. They have high chemical resistance, low melting points, high transparency, and high heat resistance and readily dissolve rare-earth element ions [7–10]. The glass formation in the system Li 2 O ⋅ B 2 O 3 –B 2 O 3 – Yb 2 O 3 ⋅ B 2 O 3 was studied previously [7]. Materials containing Li 2 O as a modifier and B 2 O 3 as a glass for- mer have ionic conduction. With increasing Li 2 O con- centration, the electrical conductivity of these materi- als increases. If more than one glass former is used, the electrical conductivity increases because of the mixed alkali effect [11, 12]. However, if two different modifi- ers are used, the conductivity decreases also because of the mixed alkali effect [13, 14]. For example, the con- ductivity of samples in the Li 2 O–B 2 O 3 –MnO system increases with increasing modifier concentration [15]. Introduction of rare-earth element oxide to a glassy material sometimes improves the optical properties of the material. This increases the refractive index, the optical band gap, and the laser gain [16]. On the other hand, the data on the conductivity of oxide materials containing rare-earth element oxides show that, with increasing concentration of rare-earth element oxide, the electrical conductivity of samples decreases [17, 18]. In some cases, conversely, addition of rare-earth element oxide, e.g., Dy 2 O 3 , increases the conductivity and decreases the glass transition temperature of V 2 O 5 –P 2 O 5 –B 2 O 3 glasses [19]. Ternary lithium borate oxides, e.g., lithium tribo- rate LiB 3 O 5 , are known as efficient nonlinear materi- als with a wide transparency range in the UV region for laser radiation conversion [20]. Analysis of the changes in the absorption spectrum of γ-irradiated Li 2 B 4 O 7 samples, both pure and doped with Yb and Co, in the range from 200 to 3200 nm indicated that the thermoluminescence properties of the doped sam- ples were enhanced [21]. A review [22] devoted to BIBO, a new nonlinear optical material based on B 2 O 3 , systematized data on the phase equilibrium in the Bi 2 O 3 –B 2 O 3 system, structure (crystallographic parameters of bismuth borates), polymorphism, growth of single crystals, and other characteristics of this material. The main prop- erties and fields of application of BIBO were consid- ered. PHYSICOCHEMICAL ANALYSIS OF INORGANIC SYSTEMS