Oksana Almjasheva

Petersburg State Electrotechnical University · Department of Physical Chemistry

The article focused on a new method (colloidal solution combustion synthesis, CSCS) for obtaining TiO2/YFeO3 nanocomposites and the photocatalytic activity (methyl violet oxidation) of the synthesized samples depending on the TiO2 content (0–10 wt%). The obtained photocatalysts’ properties were examined by means of EDXS, PXRD, nitrogen physisorptio...

Thin films based on the ternary complex oxide Bi0.50Fe0.4WOq with a cubic pyrochlore structure were obtained and used for the first time as electron-transport layers in perovskite solar cells. The measured power conversion efficiency was ∼ 4 rel% higher than that of state-of-the-art TiO2-based perovskite solar cells.

Проведён систематический анализ литературных данных по влиянию методов и условий синтеза на возможность самоорганизации ограничений роста образующихся частиц твёрдых фаз в ходе химических реакций. Показана перспективность использования таких методов для получения нанокристаллических фаз. Показано, что недостатком некоторых из подобных способов синт...

The formation of nanocrystals in the ZrO2–TiO2–H2O system during isothermal (240°C) treatment of co-precipitated hydroxides under hydrothermal conditions has been studied. The formation of solid solutions based on monoclinic ZrO2, anatase (TiO2), and a high-temperature disordered phase of variable composition ZrxTi(1–x)O4 with a scrutinyite (α-PbO2...

A systematic analysis of literature data concerning the influence of methods and conditions of synthesis on the possibility of self-organization of particle growth restrictions during chemical reactions of solid phase has been conducted. The prospects of using such methods to obtain nano-crystalline phases are shown. It is demonstrated that a disad...

The aim of the paper was to formulate the concept of controlled solution synthesis (a version of co-precipitation method) and to demonstrate its realization on several types of reactors, with a special focus on microreactors with free impinging jets (MRFIJ). The objects of this work are (i) co-precipitation method for synthesis of nanoparticles and...

To better understand the fundamental aspects of nanoparticle formation and transformation in the TiO2-H2O system the amorphous titania was synthesized as a precursor to studying crystal genesis, evolution, and transformation under heat treatment in air. The necessary depth of study was provided by comprehensive analysis using methods of PXRD, HT-PX...

Inconsistencies between ZrO2–TiO2 phase diagrams with regard to structure and phase field of the zirconium titanate existence especially in a low-temperature range motivate a detailed study of its formation. Here, nanocrystals of ZrTiO4 with scrutinyite (α-PbO2) structure were successfully synthesized by co-precipitation followed by calcination in...

It is shown that monocrystalline nanoparticles with fluorite structure are formed in the ZrO2-Y2O3 system, under hydrothermal conditions. The limiting content of Y2O3 in the nanocrystals based on zirconium dioxide is 21.7-22.6 mol.%. Yttrium oxide not included in the structure forms an amorphous phase, which is stable even upon thermal treatment at...

Ceramics based on polymorphs of the ZrO2, TiO2, and ZrTiO4 have received much attention due to their excellent thermal and chemical stability as well as outstanding electrophysical properties. Especially, zirconium titanate possesses high dielectric performance in the wide range of microwave frequency, but it is metastable below 1200 °C. Even thoug...

The minimum crystallite size in a group of oxides has been analyzed as a function of their synthesis conditions, critical nucleus size and the crystal structure parameters. Nanocrystals were synthesized by solution combustion, hydrothermal synthesis and heat treatment in air of the precipitated hy-droxides. Aluminum and iron oxides, titania and zir...

ZrO2/Y2O3 nanoparticles containing 0, 3, and 10 mol % Y2O3 were synthesized under hydrothermal conditions. The structural and optoelectronic properties of the nanoparticles were studied using appropriate measurement techniques. From the synthesized ZrO2–Y2O3 nanostructured systems, electron-conductive thin-film photoelectrodes were fabricated and u...

ZrO2–Y2O3 nanostructured systems with different yttria content (Y2O3 = 0, 3 and 10 mol.%) were synthesized under hydrothermal conditions and their structural, optical and electronic properties were investigated. Using ZrO2–Y2O3 systems the electron-conductive thin-film photoelectrodes were fabricated and used to develop the perovskite solar cells (...

Barium-doped nanocrystalline lanthanum ferrite was synthesized by the method of co-precipitation and subsequent annealing at 1000°C. The maximum degree of doping of La1−xBaxFeO3−x (x = 0.1) was established before the appearance of other phases. The introduction of Ba²⁺ cations leads to an increase in the average crystallite size from 25±4 nm for x...

The study of the lanthanide ion luminescence as a function of their environment in polymer-inorganic composites is necessary for better understanding of the electron energy transfer processes in a condensed state. From a practical point of view, these materials are promising for optics and medicine. The nanoparticles of ZrO2-LnO1.5 (Ln = Eu, Tb) so...

Here, we propose a formation mechanism for coreshell nanoparticles by selforganization in coprecipitated mixed hydroxides under hydrothermal conditions. A thermodynamic reason for this process is because of a decrease in the components’ solubilities together with an increase of structure’s dimension. As a particular example of such type of behavior...

Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formatio...

In this work, a complex physicochemical study of the formation and transformation of YFeO3 nanocrystals via glycine-nitrate combustion synthesis and heat treatment of its products was carried out. It was found the possibility of YFeO3 nanocrystals formation in three structural modifications-orthorhombic o-YFeO3 (Pnma) and two hexagonal-h1-YFeO3 and...

Zinc-doped yttrium orthoferrite nanocrystals having the perovskite structure were prepared by coprecipitation of yttrium, zinc, and iron hydroxides. The limiting zinc doping level of the yttrium ferrite to yield a ZnFe2O4 spinel second phase was determined. The yttrium orthoferrite particle size was found to be a nonmonotone function of dopant conc...

The sol-gel method was used to prepare Y1–xBax FeO3 (x = 0, 0.05, 0.1, 0.15, 0.2) nanocrystals. The influence of the dopant content on the particle size and magnetic properties of yttrium ferrite was examined.

Heat treatment of coprecipitated hydroxides in air has afforded isometric nanocrystals of rhombic yttrium, lanthanum, and gadolinium ferrites with average crystallite size 40±4 nm. It has been stated that the formation of XFeO3 (X = Y, La, Gd) nanocrystals occurs via two mechanisms, from the corresponding coprecipitated hydroxide (main route) and f...

In recent years materials based on nanocrystalline YFeO3 draw considerable research interest as the basis of innovative magnetic and magneto-optical devices. However, the size and the morphology of the nanocrystals are well-known to have a drastic influence on its functional properties. In present work, the effect of size and morphological features...

Nanopowders La1–xZnxFeO3 (nominal degree of doping xnom = 0, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, and 0.4) were synthesized by the sol–gel method using aqueous ammonia as a precipitator and were then annealed at 950°C for 60 min. From the data of X-ray powder diffraction analysis and local electron probe microanalysis, the maximum actual limit of dopi...

The state of water in the nanocrystals of zirconium dioxide prepared via hydrothermal synthesis has been studied. Water molecules are localized at the nanoparticles surface as well as in the crystal structure of tetragonal modification of zirconia. The effect of water elimination on the structural transformations in the nanocrystals has been analyz...

Specific features of the process in which oxide nanopowders are formed in a hydrothermal treatment of coprecipitated magnesium and iron oxides were studied. It was shown that the rate at which oxide nanoparticles are formed increases when reagents structurally close to the final product are used. It was found that, with the hydrothermal treatment o...

Formation of hexagonal and orthorhombic YFeO3 nanocrystals from an amorphous phase upon heat treatment of glycine–nitrate combustion products has been studied. The initial X-ray amorphous precursor has been shown to have pre-nucleus species of two types. Rapid formation of h-YFeO3 nanocrystals is explained by the presence of structurally similar pr...

The transitions of metastable tetragonal phase as well as high-temperature tetragonal phase into the low-temperature monoclinic phase upon heating and cooling were thoroughly studied in zirconia nanoparticles. High-temperature X-ray diffraction, thermal analysis and Raman spectroscopy were used to provide the systematic approach to the investigatio...

Nanocrystalline cobalt ferrite powders were synthesized by hydrothermal treatment of co-precipitated hydroxides in the conditions of an external heating of the autoclave and under microwave heating of the reaction medium. In the microwave-heating mode, the prenucleation clusters formed under ultrasonic treatment of a suspended mixture of cobalt and...

The data on phase and chemical transformations of nanosized zirconium dioxide upon annealing at 25–1300°С are presented. The in situ interaction of titanium tetrachloride with nanosized zirconia annealed at 200–800°С has been studied. The revealed regularities of the change of titanium content and the Cl/Ti ratio in the chemisorbed groups have conf...

Nanoparticles in the ZrO2-Me2O3 system (where Me = Y, Eu, Tb, Sm, Er) with different phase composition (m-ZrO2, t-ZrO2, c-ZrO2), size (5÷25 nm) and morphology (spheres, hollow spheres, rods and star structure) were obtained by hydrothermal synthesis. Photocatalytic activity was measured for the reaction of photoinduced hydrogen evolution from aqueo...

Yttrium orthoferrite nanocrystallites with hexagonal and orthorhombic structures were obtained directly by the glycine-nitrate synthesis. The nanocrystallites have plate-like morphology and are strongly agglomerated in highly porous structures, as was shown by the TEM investigation. The influences of the synthesis conditions on the yttrium orthofer...

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO2 in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperat...

Formation of nanocrystalline yttrium orthoferrite of ~30 nm average crystallite size from coprecipitated iron(III) and yttrium hydroxides was studied by thermo-X-ray diffractometry and simultaneous thermal analysis over 25–900°C temperature range. A mechanism of physicochemical transformations leading to the formation of YFeO 3 nanoparticles was su...

Nanosized yttrium orthoferrite was obtained by the heat treatment of an X_ray amorphous precursor prepared by the glycine–nitrate combustion process in orthorhombic and hexagonal phases with average crystallite sizes of 27–33 nm and 6–11 nm, respectively. The processes controlling YFeO3 formation under the specified conditions were shown to be the...

Mechanism by which nanocrystalline yttrium orthoferrite is formed in thermal treatment of amorphous nanopowders produced by the glycine–nitrate combustion method was studied. It was shown that orthorhombic YFeO 3 is formed from the amorphous phase via intermediate formation of a metastable nanocrystalline hexagonal phase of yttrium orthoferrite. Th...

We synthesized nanoparticles of variable composition based on zirconium dioxide in the ZrO2-Y2O3 (or Gd2O3)-H2O systems under hydrothermal conditions. By X-ray diffraction and small-angle X-ray scattering studies revealed that the nanoparticles consist of crystalline core and amorphous shell. Increase of Y2O3 (or Gd2O3) content yields increases of...

On the basis of specific features of the unit cell parameters of nanocrystals of variable composition synthesized via hydrothermal route, formation of crystalline core–amorphous shell nanoparticles has been suggested [1, 2]. The present work deals with combined study of the structure of nanoparticles of variable composition forming in the ZrO 2 –Gd...

Glycine-nitrate combustion method was used to obtain nanopowders of orthorhombic and hexagonal yttrium orthoferrite with particles sizes in the ranges from 30 to 53 nm and from 6 to 14 nm, respectively. It is shown that the structure and size of the particles are determined by the process temperature, which depends on the relative amounts of glycin...

Nanopowders of ferrites Y1 − x Cax FeO3 (x = 0.1, 0.2, and 0.3) were prepared by chemical coprecipitation of cations Y3+, Ca2+, and Fe3+ by an aqueous sodium carbonate solution. It was found that an increase in the calcium content leads to a decrease in the size of nanocrystals, the average size of which is 25–50 nm. Doping of yttrium orthoferrite...

Yttrium orthoferrite nanocrystals with an average crystallite size of 55 – 60 nm have been obtained under hydrothermal conditions. The influence of the hydrothermal synthesis temperature on the structure and crystallite size has been investigated. Mechanism of the YFeO3 formation under the hydrothermal conditions has been proposed.

Nanoparticles based on ZrO2 in the form of spheres, cylinders and agglomerates in the form of hollow micro- spheres were obtained. It is shown that the main factor influencing on the formation of nanostructures based on zirconium dioxide under hydrothermal conditions is the chemical prehistory of the starting materials. The possibility of varying t...

Poly(4,4′-oxydiphenylenepyromellitimide) is used as a polymer matrix for incorporation of zirconia nanoparticles with different compositions (ZrO2 and Y0.03Zr0.97O1.985), sizes (20 ± 5 and 10 ± 2 nm), and morphologies (spheres, hollow spheres, rods). The nanoparticles are incorporated during the synthesis of poly(amido acid), a prepolymer of polyim...

Influence of chemical prehistory of the precursors on chemical reactions in the ZrO2—TiO2 system under hydrothermal conditions was investigated. The possibility of formation phases with fluorite-like structure (Zr,Ti)2O4 at temperature 240°C is shown, it being process of nucleation on stage of coprecipitation of hydroxides is crucial.

We report the synthesis of Y1 − x Cd x FeO3 − δ nanocrystals in the range x = 0–0.2. The Y1 − x Cd x FeO3 − δ materials were shown to be single-phase by X-ray diffraction, with an average crystallite size from 23 to 34 nm, depending on composition. With increasing cadmium oxide content, the size of the Y1 − x Cd x FeO3 − δ nanocrystals decreases an...

We have studied the effect of the structure of precursors on the formation of Mg3Si2O5(OH)4 nanotubes under hydrothermal conditions. The results demonstrate that a chemical match between the components of a starting mixture has an advantageous effect on the synthesis of nanotubular magnesium hydrosilicate and the morphology of the hydrothermal trea...

Y3 − x Lax Fe5O12(x = 0, 0.2, 0.4, 0.6) nanocrystals have been prepared through hydroxide coprecipitation followed by dehydration. Increasing x from 0 to 0.6 reduces the particle size of the solid solution (from 54 to 43 nm), increases its unit-cell parameter, and influences its magnetic properties.

Stiffness and Young’s modulus of the natural kineral and synthetic chrysotile nanotubes were determined using atomic-force microscope. The main factors affecting the result’s accuracy were considered.

YFeO3 nanocrystals have been prepared via coprecipitation of yttrium and iron(III) chlorides with aqueous ammonia. The average size, morphology, and magnetic properties of the YFeO3 nanoparticles are shown to be highly dependent on the preparation procedure.

The size and morphology of yttrium orthoferrite nanoparticles were examined in relation to the synthesis conditions. The chemical composition of the crystalline phases resulted from heat treatment of the samples at 650°C varies with the procedure of coprecipitation of yttrium and iron(III) hydroxides. At the same time, heat treatment at 750°C leads...

The effect of nanoparticles in an aqueous dispersion (nanofluid) on the critical heat flux (CHF) removed by boiling liquid from a heat-exchange surface has been studied. It is shown that a nanoparticles layer formed on the heated surface in the course of boiling possesses a hierarchical structure. Hydrophilic properties of this layer and its high p...

The formation of CoFe2O4 nanocrystals under hydrothermal conditions at a temperature of 130°C is investigated. The average size of CoFe2O4 particles varies from 6 to 11 nm depending on the synthesis time. The hydrothermal medium is heated by two different methods, i.e., the microwave (with a synthesis time from 1 min to 2 h) and conventional (with...

Catalytic properties in relation to the hydrogen oxidation reaction and thermal stability of materials based on the nanocomposite amorphous Al2O3-nanocrystalline ZrO2 were studied.

Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the...

Desorption and adsorption of water on the surface of ZrO2 particles obtained under hydrothermal conditions were considered. The heat effect of desorption was determined.

The diffusion phase decomposition of fluorophosphate glasses doped with cadmium and manganese sulfides, as well as with cadmium sulfide and erbium oxide, is investigated using optical spectroscopy. It is revealed that a two-phase structure of the core-shell type, which consists of cadmium particles with a shell composed supposedly of cadmium sulfid...

A thermochemical investigation is undertaken on the desorption and adsorption of water on the surface of ZrO2 nanopowders. The thermal effects of the sorption processes and the temperature conditions optimum for operation of the material from the viewpoint of the desorption rate are determined. The possibility of using ZrO2 nanoparticles in devices...

The reciprocal influence of components on the chemical and structural transformations in the ZrO2-Al2O3-H2O system during nanoparticle formation under hydrothermal conditions is considered. The possibility of formation of amorphous aluminum oxide under hydrothermal conditions is found as a result of the influence of zirconia nanoparticles on the cr...

The formation of ZrO2 nanoparticles during the hydrothermal treatment of zirconium oxyhydroxide has been investigated depending on the chemical and thermal history of the initial material. It has been shown that the crystallization of c(t)-ZrO2 and m-ZrO2 under hydrothermal conditions proceeds virtually simultaneously, and the amount of one or anot...

Zirconia-based ZrO2-In2O3 nanocrystals are prepared by hydrothermal treatment of coprecipitated zirconium oxyhydroxide and indium hydroxide. Indium oxide is shown to dissolve predominantly in cubic zirconia nanocrystals. Its solubility in nanocrystalline zirconia notably exceeds the equilibrium In2O3 solubility in ZrO2 single crystals.