To maintain the single-phase nature of the cubic solid solution Ba2(Y, Cu, Mo)2O6, which is prone to polymorphism, titanium oxide was used. As a result of the synthesis by gel burning, annealing at 1000°C, and subsequent cooling in an inertial thermal mode, the cubic modification F 4̅ 3m of Ba5Y2CuMoTiO14 was obtained for the first time without an admixture of perovskite Fm3m. A comparative study of samples Ba4Y2CuMoO11 and Ba5Y2CuMoTiO14 was carried out using X-ray powder diffraction, X-ray fluorescence spectrometry, IR spectroscopy, and diffuse reflectance spectroscopy.

A new phase Ba2(Y,Cu,Mo)2O6 with the cubic perovskite structure Fm-3m has been obtained in the BaO–CuO–Y2O3–MoO3 quasiquaternary system, and the possibility of coexistence of two limited solid solutions with cubic structures Fm-3m and F-43m has been established. The samples were synthesized by gel combustion followed by calcination at 1000°C and cooling in the inertial thermal regime. The studies were carried out by X-ray phase analysis, X-ray fluorescence spectrometry, infrared spectroscopy, and diffuse reflectance spectroscopy.

Polycrystalline samples of the pseudobinary system Ba2YMoO6–[Ba2YCuO5] were synthesized using the gel combustion method. The obtained samples were investigated using X-ray diffraction and photoluminescence spectroscopy. The substitution of Mo with Cu led to the stabilization of cubic phases Fm3̅m and F4̅3m of the solid solution Ba2YMo1 – xCuxO6 – δ (0 ≤ x ≤ 0.5) in air.

Samples of Mg3 – nNinBPO7 (n = 0–3), synthesized by gel combustion followed by annealing at 980°C and cooled in the inertial-thermal mode, were studied by X‑ray powder diffraction, infrared spectroscopy, and X-ray fluorescence spectrometry. For the first time, the crystalline phase of Ni3BPO7 with the β-Zn3BPO7 structure has been experimentally obtained. When the composition of the samples changed from Mg3BPO7 to Ni3BPO7, a region of coexistence of α‑Mg3BPO7 and β-Ni3BPO7 phases was found. An analysis of the diffuse reflectance spectra of the Mg1.5Ni1.5BPO7 sample showed the presence of Ni2+ cations in an arrangement not symmetric octahedral or tetrahedral.

Mg 3 – n Ni n BPO 7 samples ( n = 0–3) were synthesized by gel combustion followed by annealing at 980°C, cooled under inertial-thermal conditions, and then studied by X-ray powder diffraction analysis, IR spectroscopy, and X-ray fluorescence spectrometry. A crystalline phase of Ni 3 BPO 7 with the β-Zn 3 BPO 7 structure was experimentally obtained for the first time. When varying the composition of the samples from Mg 3 BPO 7 to Ni 3 BPO 7 , in borophosphate, a region of coexistence of α‑Mg 3 BPO 7 and β-Ni 3 BPO 7 was discovered. Analysis of diffuse reflectance spectra of Mg 1.5 Ni 1.5 BPO 7 showed the presence of Ni 2+ cations in an environment different from the symmetrical octahedral or tetrahedral environment.

Samples of the composition Ce 0.9 (Mg 1 – x Ni x ) 0.1 O 2 (0 ≤ x ≤ 1, step x = 0.1) have been obtained by gel combustion followed by hydrothermal treatment. X-ray powder diffraction data have showed that after gel combustion and annealing at 1100°C, composite CeO 2 (fluorite structure)/solid solution Mg 1 – x Ni x O (halite structure) is formed, and additional hydrothermal treatment followed by annealing promotes the formation of limited solid solution Ce 0.9 (Mg 1 – x Ni x ) 0.1 O 2 . According to the results of IR spectroscopy, the CeO 2 /Mg 1 – x Ni x O composite does not adsorb CO 2 even in the presence of water vapor, which is also confirmed by diffuse reflectance spectra in the UV-visible region. On the contrary, the Ce 0.9 (Mg 1 – x Ni x ) 0.1 O 2 solid solution absorbs CO 2 , as evidenced by the results of IR spectroscopy and thermogravimetric analysis.

The Mg3 – nNinBPO7 (n = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) samples were prepared by solid-phase reactions at 980°C followed by inertial cooling, and then were characterized by X-ray powder diffraction, IR spectroscopy, diffusive reflectance and X-ray fluorescence spectrometry. It was for the first time that experiments yielded Ni3BPO7 crystals having the β-Zn3BPO7 non-centrosymmetrical hexagonal structure. The α-Mg3BPO7 and Ni3BPO7 coexistence range was determined. The diffuse reflectance spectra of an Mg1.5Ni1.5BPO7 sample featured a strong Ni2+ absorption band in the blue spectral range.

The Mg3 – nNinBPO7 (n = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) samples were prepared by solid-phase reactions at 980°C followed by inertial cooling, and then were characterized by X-ray powder diffraction, IR spectroscopy, diffusive reflectance and X-ray fluorescence spectrometry. It was for the first time that experiments yielded Ni3BPO7 crystals having the β-Zn3BPO7 non-centrosymmetrical hexagonal structure. The α-Mg3BPO7 and Ni3BPO7 coexistence range was determined. The diffuse reflectance spectra of an Mg1.5Ni1.5BPO7 sample featured a strong Ni2+ absorption band in the blue spectral range.

The Mg3 – nNinBPO7 (n = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) samples were prepared by solid-phase reactions at 980°C followed by inertial cooling, and then were characterized by X-ray powder diffraction, IR spectroscopy, diffusive reflectance and X-ray fluorescence spectrometry. It was for the first time that experiments yielded Ni3BPO7 crystals having the β-Zn3BPO7 non-centrosymmetrical hexagonal structure. The α-Mg3BPO7 and Ni3BPO7 coexistence range was determined. The diffuse reflectance spectra of an Mg1.5Ni1.5BPO7 sample featured a strong Ni2+ absorption band in the blue spectral range.

Samples of the composition Ce0.9(Mg1 – xNix)0.1O2 (0 ≤ x ≤ 1, step x = 0.1) have been obtained by gel combustion followed by hydrothermal treatment. X-ray powder diffraction data have showed that after gel combustion and annealing at 1100°C, composite CeO2 (fluorite structure)/solid solution Mg1 – xNixO (halite structure) is formed, and additional hydrothermal treatment followed by annealing promotes the formation of limited solid solution Ce0.9(Mg1 – xNix)0.1O2. According to the results of IR spectroscopy, the CeO2/Mg1 – xNixO composite does not adsorb CO2 even in the presence of water vapor, which is also confirmed by diffuse reflectance spectra in the UV-visible region. On the contrary, the Ce0.9(Mg1 – xNix)0.1O2 solid solution absorbs CO2, as evidenced by the results of IR spectroscopy and thermogravimetric analysis.

The crystalline phase of Mg3BPO7 was obtained by gel combustion method and solid-phase synthesis with optimization of annealing temperatures. The effect of precursors and synthesis conditions on the formation of Mg3BPO7 was analyzed by X-ray powder diffraction and IR spectroscopy. It was shown that the formation of a mixture of kotoite Mg3B2O6 and farringtonite Mg3P2O8 prevents the formation of Mg3BPO7, whereas a significant excess of periclase MgO promotes the production of Mg3BPO7.

Samples of the composition Ce0.9(Mg1 – xNix)0.1O2 (0 ≤ x ≤ 1, step x = 0.1) have been obtained by gel combustion followed by hydrothermal treatment. X-ray powder diffraction data have showed that after gel combustion and annealing at 1100°C, composite CeO2 (fluorite structure)/solid solution Mg1 – xNixO (halite structure) is formed, and additional hydrothermal treatment followed by annealing promotes the formation of limited solid solution Ce0.9(Mg1 – xNix)0.1O2. According to the results of IR spectroscopy, the CeO2/Mg1 – xNixO composite does not adsorb CO2 even in the presence of water vapor, which is also confirmed by diffuse reflectance spectra in the UV-visible region. On the contrary, the Ce0.9(Mg1 – xNix)0.1O2 solid solution absorbs CO2, as evidenced by the results of IR spectroscopy and thermogravimetric analysis.

The boundaries of Mg1 – xNixGa2O4 solid solutions (0 ≤ х ≤ 0.5) with a spinel structure synthesized by the gel combustion method, annealed at 1000°C, and furnace cooled have been experimentally determined for the first time. Mg1 – xNixGa2O4 samples (0 ≤ х ≤ 1, step х = 0.1) with an inverse spinel structure have been studied by X-ray diffraction and IR spectroscopy. It has been found that the range of the (Mg,Ni)Ga2O4 solid solution can deviate from the line connecting the stoichiometric compositions MgGa2O4 and NiGa2O4. The diffuse reflectance spectra of Mg0.9Ni0.1Ga2O4 and Mg0.5Ni0.5Ga2O4 spinels show an intense absorption band corresponding to Ni2+ in the near-IR range, which is of great interest for using this property in laser and optoelectronic technologies with minimal negative impact on the environment.

Samples of the initial composition Mg1 – xNixGa2O4 (0 ≤ х ≤ 1, step х = 0.1) synthesized by the gel combustion method and annealed at 1000°C have been studied by X-ray powder diffraction and IR spectroscopy. For homogeneous samples of (Mg,Ni)Ga2O4 with a spinel structure, the gallium nonstoichiometry has been determined by inductively coupled plasma atomic emission spectrometry. Within the framework of the MgO–NiO–Ga2O3 system, the boundary of the homogeneity region of spinel (Mg,Ni)Ga2O4, which is in equilibrium with halite (Mg,Ni)O, has been outlined. An analysis of the diffuse reflectance spectra of (Mg,Ni)Ga2O4 in the range of 350–900 nm revealed intense absorption bands from Ni2+ in octahedral positions and showed an increase in their intensity with an increase in the nickel content in the spinel.

Mg 1 – x (BP) x /2 O 1 + x , Mg 3 B 2 – 2 x P 2 x O 6 + 2 x , Mg 2 B 2 – 2 x P 2 x O 5 + 2 x , and MgB 2 – 2 x P 2 x O 4 + x (0 ≤ х ≤ 1, х = 0.1 step) samples prepared by gel combustion or solid-phase sintering and then annealed at 1000°C were characterized by X-ray powder diffraction. An Mg 3 BPO 7 crystal phase was prepared and characterized by IR spectroscopy and scanning electron microscopy. Stable and metastable equilibrium phase diagrams were plotted for the 2MgO–B 2 O 3 –P 2 O 5 quasi-ternary system.

The ionic and phase compositions of Y2.5Ce0.5Fe2.5Ga2.5O12 ferrogarnet samples obtained by gel combustion with subsequent vacuum annealing were studied for the first time by X-ray photoelectron spectroscopy and X-ray powder diffraction analysis. The X-ray powder diffraction data confirmed the phase homogeneity of Y2.5Ce0.5Fe2.5Ga2.5O12 and the absence of a cerium dioxide impurity. At the same time, on the surface of Y2.5Ce0.5Fe2.5Ga2.5O12 particles, along with Ce3+, there are Ce4+ ions.

The samples of LiMn2−xBxO4 (0 ≤ x ≤ 2, step x = 0.1) were synthesized by gel combustion with polyvinyl alcohol. To obtain samples of Li (Ni0.4Mn0.3Co0.3)1−zBzO2 (0 ≤ z ≤ 1, step z = 0.1), LiNi0.4Mn0.3Co0.3O2 was synthesized separately by gel combustion with starch, and afterwards sintered with LiBO2. Based on x-ray diffraction data, the boundary compositions LiMn1.5B0.5O4 and Li (Ni0.4Mn0.3Co0.3)0.9B0.1O2 for solid solutions with spinel and α-NaFeO2 structures were established. The change in the elementary cell parameters of solid solutions depending on the boron content was analysed. Electrochemical testing of LiMn1.8B0.2O4 and LiMn1.5B0.5O4 samples was performed. Phase equilibria between the crystalline phases of the Li-Mn-B-O system under isobaric-isothermal conditions were presented.

The homogeneous solid solution Ti1 – x(BP)x/2O2 (0 ≤ х ≤ 0.2) with the anatase structure was obtained by gel combustion with polyvinyl alcohol. The possibility of combined replacement of titanium atoms in the anatase structure with boron and phosphorus was determined by studying samples of the Ti1– x(BP)x/2O2 series (0 ≤ х ≤ 1, step х = 0.1) by powder X-ray diffraction and IR spectroscopy. The obtained data were used to construct the TiO2–B2O3–P2O5 phase diagram describing phase equilibria involving Ti1 – x(BP)x/2O2 solid solution (0 ≤ х ≤ 0.2), Ti5P4O20, TiP2O7, BPO4, and the melt. Analysis of the absorption spectra of Ti0.9B0.05P0.05O2 and Ti0.8B0.1P0.1O2 in the 290–1000 nm range demonstrated that the equimolar introduction of B and P into anatase shifts the absorption edge to the red region. The specific surface area, skeletal density, and the particle size of Ti0.8B0.1P0.1O2 with the anatase structure were determined.