Order–disorder structural transformations in xR2O3·(1 – х)TiO2 (R = Yb, Lu; х = 0.5–0.6) solid solutions with a highly imperfect fluorite-derived structure at 1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two cubic phases identical in composition: a disordered fluorite-like (F) phase (Fm3m) and an ordered pyrochlore-like (P) phase (Fd3m), which is coherent with the disordered phase and consists of nanoscale (<100 Å) and nanocrystalline domains. The lattice parameters of these phases have been determined. The stability range of the solid solutions in the systems studied is 0.5 ≤ x ≤ 0.55. In the samples containing 0.55Yb2O3 and 0.5Lu2O3, the P-phase consists of nanodomains. The Raman spectra of the Yb2TiO5- and Lu2TiO5-based solid solutions contain broad bands at low and high frequencies, with peaks at 101, 175, 290, 346, 384, and 727 (115, 176, 320, and 745) cm–1, which correspond to the P- and F-phases, respectively. The formation of pyrochlore-like phases with different degrees of order in a fluorite matrix is due to the internal stress induced by the high density of structural defects in their unit cells. The materials obtained in this study have a large specific surface area and can be used as catalysts and catalyst supports.

The ZrNi1.2Mn0.5Cr0.2V0.1 alloy was qualified using isotherms of hydrogen desorption in a gas atmosphere, equilibrium curves of hydrogen desorption in a 30% KOH solution, and X-ray diffraction data. The equilibrium pressure of the ZrNi1.2Mn0.5Cr0.2V0.1 alloy in a gas atmosphere at 20°C that was equal to ~1 atm (101,325 Pa) indicated that the alloy could be used in Ni–MH batteries, and the equilibrium hydrogen desorption curve obtained by the electrochemical method indicated that insignificant self-discharge could occur. The alloy samples crystallized at different cooling rates showed different quantitative phase composition. Electrodes produced from the sample with a greater amount of the Zr7Ni10 phase activated faster and those with a greater amount of the C15 and C14 phases had higher maximum discharge capacity. After the electrodes were exposed to air for 14 days, the Zr7Ni10 phase decreased by 7 vol.% and the total content of the C15 and C14 phases increased by 7 vol.% in the sample with a greater amount of the Zr7Ni10 phase (~ 24 vol.%). No changes in quantitative phase composition were found in the sample with a smaller amount of the Zr7Ni10 phase (~12 vol.%). Electrodes prepared from the sample with a lower content of the Zr7Ni10 phase showed better cyclic stability both before and after a pause in the cycles. The loss of the maximum achieved discharge capacity of these electrodes for 100 cycles with a pause in the cycles for 14 days (after the 80th cycle) and for 200 cycles with a pause in the cycles for 45 days (after the 150th cycle) was only 2 and 16%, and that of the electrodes with a higher content of the Zr7Ni10 phase was 30 and 52%. Thus, the electrodes produced from the alloy sample that showed stable quantitative phase composition according to X-ray diffraction had better hydrogenation–dehydrogenation cyclic stability when exposed to air in powder form for 14 days. Taking into account some similarities in hydrogenation-dehydrogenation and exposure to air of the zirconium alloys (oxidation of alloy components, significant increase in nickel surface concentration, etc.), the better cyclic stability of the electrodes was logically assumed to be due to more stable quantitative phase composition of the surface. The relationship between the electrochemical properties of the ZrNi1.2Mn0.5Cr0.2V0.1 alloy and the cooling rate in crystallization (quantitative phase composition) allows the development of materials with predicted functional properties.

We study Al3Sc, Al3Zr, Al3Hf, and Al3V intermetallic compounds playing the role of hardening phase in aluminum alloys. We use the technology of rapid crystallization from the liquid state. We obtain relatively fine grains d ∼ 15 μm in size for cast materials. By the method of X-ray diffraction analysis, it is shown that the Al3Zr intermetallic compound is a single-phase material, whereas the Al3Sc, Al3Hf, and Al3V intermetallics consist of several phases. The investigation of the mechanical characteristics by the indentation method shows that the Al3Hf intermetallic has the maximum hardness HV = 6.75 GPa and the maximum yield stress σSH = 4.86 GPa, whereas the Al3Sc intermetallic has the minimum hardness HV = 2.0 GPa, the minimum yield strength σSH = 0.86 GPa and the most plastic phase δH = 0.88. It is established that, in a 3

In the present work erbium and thulium molybdates Ln(5.5)MoO(11.25-delta) (Ln = Er and Tm) with fluorite and Ln(6)MoO(12-delta) (Ln = Er and Tm) with bixbyite structure have been studied. The materials have been obtained by mechanical activation method followed by sintering at 1600 degrees C for 3 h. New compounds have been characterized by X-ray diffraction. The total conductivity was investigated using impedance spectroscopy method in dry and wet air. Oxygen diffusivity data was acquired by oxygen isotope exchange with (CO2)-O-18. The combination of different techniques allowed us to determine ionic conductivity components in these compounds. Er and Tm fluorites and bixbyites showed oxygen-ion conductivity in dry air and oxygen-ion and proton conductivity in wet air up to 550-600 degrees C. In wet atmosphere Er and Tm fluorites and bixbyites have total conductivity of about 2.10(-6) S/cm at 500 degrees C. At higher temperatures they are mixed oxygen-electronic conductors in dry and wet atmosphere. At lower (T < 400 degrees C) temperatures bixbyites are slightly better ionic conductors compared to fluorites. A high oxygen-ion mobility in all compounds above 200 degrees C has been confirmed by isotope exchange method with (CO2)-O-18: tracer diffusion coefficient values were similar to 10(-11) - 10(-10) cm(2)/s at 700 degrees C. Fluorites were demonstrated to have a higher oxygen mobility compared to bixbyites; the effect is more pronounced for Tm molybdates. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

We have studied the structure and proton conductivity of rhombohedral La6-xMoO12-delta (x = 0.5, 0.6, 0.7, 1) lanthanum molybdates prepared via mechanical activation of lanthanum and molybdenum oxides, followed by thermal annealing at 1650 degrees C. The La6-xMoO12-delta (x = 0.5, 0.6) materials were phase-pure and had a complex rhombohedral structure (R1). An increase in the molybdenum concentration leads to a decrease in the degree of rhombohedral distortion and proton conductivity in the La6-xMoO12-delta (x = 0.5, 0.6, 0.7, 1) series. The proton conductivity at the optimal composition La6-xMoO12-delta (x = 0.5) is similar to 4.0 x 10(-5) S/cm at 500 degrees C in wet air. A comparative analysis shows that, in the Ln(6-x)MoO(12-delta) (Ln = La, Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb; x = 0-1) series, proton conductivity decreases with the Ln ionic radii decreasing regardless of the structural type. Because of this, the high proton conductivity is demostrated by the stable La6-xMoO12-delta (x = 0.5, 0.6) materials, with an inherently deficient oxygen sublattice, which crystallize in a large-volume, complex rhombohedral cell (R1). (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Gas-tight Nd2 − xCaxZr2O7 − δ (x = 0, 0.05) pyrochlore materials have been prepared via mechanical activation of Nd2O3, ZrO2, and CaO, followed by single-step sintering of green compacts at 1600 °C for 3 or 10 h. Their structure has been studied using Rietveld refinement of X-ray diffraction data; their microstructure has been examined by scanning electron microscopy, and their conductivity has been determined by impedance spectroscopy in dry and wet air. In addition, we have assessed the effect of prolonged hydration on the proton conductivity of the Nd2 − xCaxZr2O7 − δ (x = 0, 0.05) pyrochlores. According to the Rietveld refinement results, Ca cations are incorporated into both Nd- and Zr- sub-lattice in Nd2 − xCaxZr2O7 − δ (x = 0.05) synthesized at 1600 °C, and most of the Ca cations reside on the Zr sites. The 500 °C proton conductivity of Nd2Zr2O7 is 5 × 10−6 S/cm (~ 1 × 10−5 S/cm at 600 °C) and that of Nd2 − xCaxZr2O7 − δ (x = 0.05) is 7 × 10−5 S/cm (~ 2.5 × 10−4 S/cm at 600 °C). Prolonged (5 months) immersion in water at room temperature has been shown to reduce the proton conductivity of Nd2 − xCaxZr2O7 − δ (x = 0, 0.05), which is attributable to partial dissolution of Nd and Ca. CaO and, to a considerably lesser extent, Nd2O3 segregation on polished and thermally etched (1450 °C) sections of the ceramics has been demonstrated. We attribute both effects to the high diffusion mobility of Ca2+ and Nd3+ cations, due to the basicity of their oxides in ambient air and water.

— Order–disorder structural transformations in x R 2 O 3 ∙ (1 – х )TiO 2 (R = Tm, Er; х = 0.5−0.6) solid solutions with a highly imperfect fluorite-derived structure at 1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two cubic phases identical in composition: a disordered fluorite-like ( F ) phase ( Fm 3 m ) and an ordered pyrochlore-like ( P ) phase ( Fd 3 m ), which is coherent with the disordered phase and consists of nanoscale (<100 Å) and nanocrystalline domains. The lattice parameters of these phases have been determined. In the stability range of the solid solutions ((0.5 ≤ x ≤ 0.6)), the lattice parameter of the fluorite-like phases follows Vegard’s law. The Raman spectra of the R 2 TiO 5 -based (R = Tm, Er) solid solutions contain broad bands at low and high frequencies, with peaks at 100, 171, 291, 355, 385, and 723 cm –1 for R = Tm and at 100, 169, 292, 355, 390, and 720 cm –1 for R = Er, which correspond to the P - and F -phases, respectively. The formation of pyrochlore-like phases with different degrees of order in a fluorite matrix is due to the internal stress induced by the high density of structural defects in their unit cells. The materials obtained in this study have a large specific surface area and can be used as catalysts and catalyst supports.

Using mechanical activation of appropriate Nd2O3 + HfO2 mixtures, followed by single-step high-temperature (1600-1700 degrees C) annealing of green compacts, we have synthesized pyrochlore solid solutions in an isomorphous miscibility range around the nominally stoichiometric composition Nd2Hf2O7: (Nd2-xHfx)Hf2O7+x/2 (x = 0.2, 0.32, 0.39); Nd-2(Hf2-xNdx)O7-x/2 (x( )= 0, 0.1). After annealing at 1700 degrees C for 5 h, only the Nd-2(Hf2-xNdx)O-7(x = 0, 0.1) materials with the pyrochlore structure were single-phase, whereas after annealing at the lower temperature, 1600 degrees C, for 10 h only nominally stoichiometric Nd2Hf2O7 was free of impurities. The pyrochlore phases (Nd2-xHfx)Hf2O7+x/2 (x = 0.2), Nd2Hf2O7, Nd-2(Hf(2-x)Ln(x))O7-x/2 (x = 0.1) have been characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and impedance spectroscopy. The order-disorder (pyrochlore-fluorite) transition in the Nd2Hf2O7-Nd2O3 isomorphous miscibility range has been studied by Raman spectroscopy and XRD. The two-phase (Nd2-xHfx)Hf2O7+x/2(x= 0.2) material has been shown to have the brightest luminescence. A gas-tight Nd-2(Hf2-xNdx)O7-x/2 (x = 0.1) ceramic (with a density of similar to 95.1%) has been produced by high- temperature annealing at 1700 degrees C. Neodymium oxide segregation has been detected by SEM on polished sections of the (Nd-2(Hf2-xNdx)O7-x/2 (x = 0, 0.1) ceramics in air and attributed to Nd3+ diffusion from the hafnates at a thermal etching temperature of 1450 degrees C. For the first time, proton conductivity was found both in Nd2Hf2O7 (1.25 x 10(-6) S/cm at 700 degrees C) and Nd-2(Hf2-xNdx)O7-x/2 (x = 0.1) (similar to 1 x 10(-4) S/cm at 700 degrees C). The ionic conductivity maximum of Nd2Hf2O7 in dry air was similar to 1 x 10(-6) S/cm at 700 degrees C, which is almost an order of magnitude higher than was reported in the literature before.

Sm2−xCaxZr2O7−x/2 (x = 0, 0.05, 0.1) and Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore–fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100–900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700–950 °C. The Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen–ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) is ~ 1 × 10−4 S/cm. The fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) to fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2−xCax)Zr2O7−δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2−xCaxZr2O7−x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.

Based on rhombohedral structure (R3̄) complex Nd10Mo2O21 compound has proton conductivity ∼8 × 10−4 S cm−1 at 600 °C.

Order–disorder phenomena in nanocrystalline Gd 2 ZrO 5 and Gd 2 HfO 5 with highly imperfect fluorite- derived structures in the range 1000–1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two coherent phases identical in composition: a nanocrystalline disordered fluorite-like (F) phase ( Fm3m ) and a nanoparticulate ordered fluorite derivative ( C 1 ) ( Ia 3). Their lattice parameters have been determined. In the range 1000–1600°C, the Raman spectra of the Gd 2 ZrO 5 and Gd 2 HfO 5 materials contain broad bands in low- and high-frequency regions, at ~118 (108), 362 (353), and 670 (665) cm –1 , which characterize the C 1 and F phases, respectively.

Аннотация – Методами РФА и КР-спектроскопии исследованы вольфраматы (La6WO12, La5.5WO11.25) и молибдаты (La5.5MoO11.25, La5.8Zr0.2MoO12.1) лантана – практически важные материалы для электролитов протонпроводящих твердооксидных топливных элементов и протонпроводящих мембран. Молибдаты и вольфраматы лантана синтезированы с использованием метода механической активации оксидов с последующим отжигом при высоких температурах 1600 и 1650°C. Практически однофазные материалы La6WO12 и La5.5WO11.25 со структурой двойного флюорита были получены при 1650°C в течение 3 ч. После отжига при более низкой температуре (1600°C) материалы номинального состава La6WO12 и La5.5WO11.25 - двухфазные и содержат примесь La2O3 (~5%). Ромбоэдрические молибдаты La5.5MoO11.25 и La5.8Zr0.2MoO12.1 являются однофазными материалами в температурном интервале 1600–1650°C. Согласно смешанным КР-люминесцентным спектрам, наиболее разупорядоченными с позиции молекулярной структуры являются высокопроводящие вольфраматы лантана (La6WO12, La5.5WO11.25) , полученные при 1600 и 1650°C. Abstract – X-ray diffraction and Raman spectroscopy study of lanthanum tungstates (La6WO12, La5.5WO11.25) and molybdates (La5.5MoO11.25, La5.8Zr0.2MoO12.1) has been performed taking into account the fact that these ceramic materials are practically important for applying as electrolytes for solid oxide fuel cells (SOFCs) and proton conducting membranes. Lanthanum molybdates and tungstates have been synthesized using a procedure for mechanical activation of oxides followed by annealing at high temperatures, i.e. 1600 and 1650°C. Substantially single-phase materials La6WO12 and La5.5WO11.25 with a double fluorite structure have been obtained at 1650°C within 3 h. The products annealed at a lower temperature (1600°C) with a nominal composition of La6WO12 and La5.5WO11.25 are characterized by two-phase structure and the presence of an admixture of La2O3 (~5%). Lanthanum molybdates La5.5MoO11.25 and La5.8Zr0.2MoO12.1 synthesized in the temperature range of 1600-1650°C are shown to have rhombohedral single-phase structure. According to mixed Raman-luminescence spectra, the high-conducting lanthanum tungstates (La6WO12, La5.5WO11.25) synthesized at 1600 and 1650°C are found to be the most disordered ones from the viewpoint of their molecular structure.

The synthesis of the Ln(6)MoO(12) (Ln = Sm, Ho -Yb) (3:1) rare-earth molybdates from binary oxides at room temperature has been studied by XRD and electron spin resonance spectroscopy (ESR). The mechanical activation of 3Ln(2)O(3) + MoO3 (Ln = Sm, Ho, Yb) mixtures containing unmilled or premilled MoO3 initiates the formation of Lri(6)MoO(12) (Ln = Sm, Ho-Yb) at room temperature, which is accompanied by a reduction in the ESR signal from Mo5+ paramagnetic ions located on the surface of the activated Mo03 and, hence, by a reduction in the amount of MoO3 in the mixture, due to reaction with Ln(2)O(3) (Ln = Sm, Ho, Yb).The major phase resulting from the mechanochemical synthesis is a cubic phase with the bixbyite structure (la(-3), no. 206) for Ln(6-x)MoO(12-delta) (Ln = Dy -Yb; x = 0, 0.5) and the Sm2O3 type structure (C 2/m, no. 12) for Ln(6)MoO(12) (Ln = Gd, Sm). The high-temperature synthesis of Ln(6-x)MoO(12-delta) (Ln = Ho -Yb; x = 0, 0.5) and Ho1oMo2021 from precursors prepared at room temperature has been studied at 1200 degrees C and heat treatment times of 4, 40, 80, and 160 h. The bixbyite phase disappears because it is metastable and is formed due to kinetic factors in the stability field of lower symmetry phases: tetragonal (T) and rhombohedral (R3). We have located the stability range of the rhombohedral (R3) phase as a function of Ln below 1200 degrees C using different heating time. We have found conditions for the synthesis of the tetragonal phase T, which exists only in the case of the intermediate lanthanides. The tetragonal phase in phase-pure form has been synthesized for the first time via prolonged (160 h) heat treatment of Ho10Mo2O21 at 1200 degrees C. The electrical conductivity of the samples with different % of tetragonal phase has been measured by impedance spectroscopy in dry and wet air. The Arrhenius plot of conductivity for pure tetragonal phase has the form of straight line over the entire temperature range studied, 440-900 degrees C (Ea = 1.37 eV, a 600 degrees C = 1 x 10(5) S cm(-1)) in dry and wet air. The absence of electrode dispersions at low frequencies and conductivity growth in a wet air makes us assume the predominantly electronic conductivity type of the Ho1oMo2021 tetragonal phase in the temperature range 440-900 degrees C. In multiphase samples surface electronic conductivity is observed up to 620-650 degrees C in wet air, which is associated with the presence of defects at grain boundaries of crystallographically related phases (bixbyite, rhombohedral and tetragonal phases).

The film photoanodes based on CdSe and NT-TiO2/CdSe have been formed by the electrochemical and painting methods. It is shown that the introduction of graphene oxide into the structure of the semiconductor CdSe film promotes absorption of light and leads to improvement in their characteristics by 25-30 %. The compatibility of the cathode based on composite of hydrogensorbing intermetallic alloys LaNi4.5Mn0.5 + LaNi(3.5)Al(0.7)Mn(0.8 )with current-conductive additives in pair with the CdSe photoanode is shown. It was found that 95 - 98 % of the total current generated under the influence of sunlight at the anodes was used on the formation and accumulation of hydrogen by cathodes.

Zr-substituted rare-earth molybdates Ho5.4Zr0.6MoO12.3 and unsubstituted La5.5MoO11.25 demonstrate appreciable mixed electron-proton conductivity in the 200-470 degrees C and 145-730 degrees C temperature range, respectively, under wet oxidizing and mild reducing conditions (air, Ar, Ar-5% H-2). Rhombohedral fluorite-like La5.5MoO11.25 showed the highest bulk conductivity of about 1x10(-5)S/cm at 400 degrees C in wet air and Ar. Its impedance spectra did not provide any evidence of the grain boundary contribution in wet atmosphere. Total conductivity of Ho5.4Zr0.6MoO12.3 fluorite is much lower and is 3x10(-7) S/cm at 400 degrees C in wet air. Besides, it should be noted that there is a grain-boundary contribution of Ho5.4Zr0.6MoO12.3 in wet air and Ar. Thermogravimetry data demonstrate that the fraction of strong structurally bound water and interstitial protons in La5.5MoO11.25 and Ho5.4Zr0.6MoO12.3 is similar to 0.02-0.03% in the range similar to 600-900 degrees C. The stability of Ho5.4Zr0.6MoO12.3 fluorite structure and fluorite-like rhombohedral La5.5MoO11.25 structure in extremely dry conditions under dynamic vacuum of 10(-6)-10(-7) mbar was investigated by in situ variable temperature neutron diffraction between 800 and 1400 degrees C to understand phase behaviour under mild reducing conditions in a wide temperature range. Rhombohedral fluorite-like La5.5MoO11.25 has been shown to be more resistant to reduction under vacuum below 1100 degrees C in heatingcooling cycles than is fluorite Ho5.4Zr0.6MoO12.3. Given the higher proton conductivity of Ln(5.5)MoO(11.25), this suggests that rhombohedral fluorite-like La6MoO12 - based molybdates are suitable for long-term use under mild reducing conditions and 600-800 degrees C.

Arrhenius plots of the total conductivity in (1 and 3) dry and (2 and 4) wet air of two Yb6MoO12 polymorphs: (1 and 2) bixbyite (Ia3̄(206)) Yb6MoO12 and (3 and 4) rhombohedral (R3̄) Yb6MoO12; Yb6MoO12 rhombohedral (R3̄) → Yb6MoO12 bixbyite (Ia3̄(206)) at T ∼ 1600 °C.