G. K. Strukova

Fine sructure of Na5Lu9F32 nanocrystallites formed at the initial stages of crystallization

X-ray diffraction investigations have demonstrated that the initial stages of the formation and growth of Na5Lu9F32 nanocrystallites from a powder mixture of lutetium fluoride, ammonium fluoride, and sodium fluoride during the solid-phase synthesis are accompanied by complex structural transformations, among which a cyclic transformation of the type single-phase → two-phase → single-phase state can be distinguished. It is shown that the two-phase state consists of two isomorphous phases with a small misfit of the lattice parameters. The isomorphous phases have common extended interphase boundaries, along which a continuous change of the lattice parameters occurs as one phase transforms into the other. A long-term annealing of the two-phase state leads to the final single-phase state, which is characterized by the growth of nanocrystallites to the scale of microcrystallites.

Specific features of the effect of dopants on the phase formation of YBO3 and ScBO3 during synthesis from the amorphous precursor state

The effect of dopants on the structural states of the YBO3 and ScBO3 borates during sequential isothermal annealings of the amorphous precursor state and the batch from a mixture of micropowders of initial rare-earth metal oxides of the same composition has been investigated using X-ray diffraction. It has been demonstrated that, in both cases, the phase sequences of rare-earth metal borates differ substantially from each other. Possible factors responsible for the strong effect of dopants on the structural sequences during the synthesis of the YBO3 and ScBO3 borates from the amorphous precursor state have been analyzed.

Anomalous structural states of rare-earth oxides in solid-phase synthesis during continuous heating

The kinetics of solid-phase synthesis of complex rare-earth (RE) oxides from an amorphous precursor state during continuous heating is studied by X-ray diffraction. Using the synthesis of RE borates (ReBO3) as an example, it is shown that a continuous heating of such precursors stimulates the formation of new phases which are unknown in an equilibrium state of one rare-earth element but known for other rare-earth borates. It is established that the regime of continuous heating during solid-phase synthesis of garnets (Re3M5O12) exhibiting the only crystal phase state for all rare-earth atoms results in an accelerated growth of crystallites and that the higher the heating rate the higher the growth rate.

Structural infection and anomalous phase sequences in complex oxides prepared from nanodispersed components

The complex oxides prepared by solid-phase synthesis from nanoscopic components are studied using X-ray diffraction. It is demonstrated that the use of nanoscopic components in the solid-phase synthesis of lutetium borate LuBO3 and europium molybdate Eu2(MoO4)3 leads to anomalous sequences of phase transformations in these compounds: the vaterite ⇒ calcite ⇔ vaterite sequence for LuBO3 and the β ⇒ α ⇔ β sequence for Eu2(MoO4)3 are observed instead of the previously known sequences, namely, the calcite ⇔ vaterite sequence for LuBO3 and the α ⇔ β sequence for Eu2(MoO4)3. The revealed anomalous sequences do not depend on the procedure used for preparing reactants and are determined by the nanoscopic sizes of the initial components. It is found that microscopic additions of a number of simple oxides can suppress the kinetics of solid-phase synthesis of particular complex oxides and initiate the formation of new phases in the synthesis of other complex oxides (the so-called structural infection effect).

“Isomorphous” phases in nanodispersed powders of rare-earth oxides

Using x-ray diffraction, a structural state consisting of two “isomorphous” phases was revealed in nanocrystalline powders of simple oxides Re2O3 (Re = Eu, Gd, La, Lu) and Y3Ga5O12 prepared by solvent thermolysis from simple-oxide solutions followed by annealing of obtained precursors at elevated temperatures. A model is proposed explaining such two-phase states in terms of the excess energy of nanograin surface layers which causes the formation of a surface phase isomorphous to the core phase having a smaller lattice parameter. Analogous two-phase states were also obtained in microcrystalline LuBO3 and Eu2(MoO4)3 powders subjected to long-term grinding.

Features of the doping effect on YAlO3 phase sequences during synthesis from an amorphous precursor state

Using X-ray diffraction methods, it has been shown that small lanthanum (La) dopants during solid-phase synthesis of YAlO3 from an amorphous precursor state initiate the formation of the high-temperature hexagonal modification of yttrium aluminate in the first crystallization stages, whereas the equilibrium perovskite phase has an orthorhombic cell. At the same time, during YAlO3 synthesis without dopants, yttrium-aluminum garnet Y3Al5O12 is formed in the first crystallization stages, rather than the perovskite modification, as it follows from the precursor stoichiometry. The effect of lanthanum dopants on YAlO3 phase sequences during synthesis from the amorphous precursor state is qualitatively explained.

Mesoscopic Models of Plants Composed of Metallic Nanowires

Various metallic structures of complex shape resembling living plant organisms (biomimetics) are produced as a result of self-assembly of nanowires growing on porous membranes in the course of pulse current electrodeposition. These structures occur if the electroplating is continued after the nanowires appear on the membrane surface. By varying the membrane geometry, pulse current electroplating parameters, and alternating electrodeposition from two baths composed of a variety of electrolytes, diverse models were fabricated, including a hollow container with a wall thickness of 10 nm–20 nm. This biomimetic method suggests an analogy between the shape-forming processes of plants and their metallic models. Nanostructured mesostructures of various metals (Ag, Pd, Ni), alloys (PdNi, PbIn) and hybrid structures (PdNi/Pb, PdNi/PbIn) were obtained. They can be of interest for fundamental research (self-assembly, morphogenesis) as well as for applications in nanotechnology (catalysis, nanoplasmonics, medicine, superhydrophobic surfaces).

Structure of precursors of complex oxides of rare-earth elements prepared by solvent thermolysis

X-ray diffraction and electron microscopy were used to study the structural states of precursors of borates LuBO3, YBO3, and EuBO3, garnets Lu3Al5O12 and Y3Al5O12, and perovskites LuAlO3 and LaAlO3 prepared by solvent thermolysis from a nitric-acid solution or an ammonium nitrate melt solution of simple oxides and nitrates of rare-earth elements. The precursors are mainly found to be amorphous. In some cases, small amounts of non-reacted initial oxides and nitrates are observed to be in an amorphous matrix.

Features of LaBO3 phase formation during solid-phase synthesis from the amorphous precursor state

The features of the phase formation of pure lanthanum borate during solid-phase synthesis from an amorphous precursor state and from a homogenized mixture of initial oxide micropowders have been investigated using X-ray diffraction methods. It has been shown that LaBO3 phase sequences obtained in both cases significantly differ from each other. The role of cross doping with Y, Sc, and La on the La0.95Sc0.05BO3, La0.95Y0.05BO3, Y0.95La0.05BO3, and Sc0.95La0.05BO3 phase sequence during synthesis from the amorphous precursor state has been clarified.