O. B. Shcherbina

Mechanical properties of Nb2O5 and Ta2O5 prepared by different procedures

We have studied the mechanical properties of niobium pentoxide and tantalum pentoxide ceramics prepared by a conventional ceramic processing technique and by exposure to high-intensity light (HIL). The results demonstrate that, after HIL exposure in an optical furnace, the niobium pentoxide and tantalum pentoxide ceramics possess enhanced microhardness and improved mechanical properties (strength, fracture toughness, and brittle microstrength) owing to the formation of fractal micro- and nanostructures. With increasing exposure intensity, the strength of the Nb2O5 and Ta2O5 ceramics increases.

Micro- and nanostructures in lithium niobate single crystals doped with lanthanides

Lithium niobate single crystals doped with lanthanides (Gd, Er) and nominally pure single crystals of congruent and stoichiometric compositions have been grown under time-dependent thermal conditions. Regular growth domain microstructures and periodic nanostructures have been investigated by optical microscopy and atomic force microscopy with a step from 10 to 100 nm. Comparative investigations of the Raman spectra of lithium niobate single crystals of different compositions have been performed.

Structure and mechanical characteristics of ceramic Nb2O5 and Nb2(1 − y)Ta2yO5

The structure and mechanical characteristics of ceramic Nb2O5 and ceramic materials produced from coprecipitated Nb2(1 − y)Ta2yO5 pentoxides by a conventional ceramic processing technique and exposure to high-intensity light have been studied by scanning probe microscopy and Raman spectroscopy.

Growth of LiNbO3:Er Crystals and concentration dependences of their properties

A series of lithium niobate (LiNbO3) crystals of congruent and stoichiometric compositions, doped with erbium, have been grown under non-steady-state thermal conditions. A series of LiNbO3:Zn crystals, nominally pure LiNbO3 crystals of congruent and stoichiometric compositions, and a LiNbO3:B crystal have also been grown. Both growth conditions and concentration dependences of physicochemical, ferroelectric, and structural characteristics of LiNbO3:Er crystals are investigated. The growth regular domain microstructures and periodic nanostructures in LiNbO3:Er crystals are analyzed by optical microscopy and atomic force microscopy (AFM). A comparative study of the optical homogeneity and photorefractive properties of LiNbO3:Er crystals of congruent and stoichiometric compositions and the Raman spectra of LiNbO3 crystals of different compositions is performed.

Effect of high-intensity light on the micro- and nanostructuring and thermal expansion of Ta2O5 and Nb2O5 ceramics

This paper examines the effect of exposure to high-intensity light on the formation of fractal micro- and nanostructures and the thermal expansion of tantalum pentoxide and niobium pentoxide ceramics. After such processing, the thermal expansion curve of Ta2O5 shows anomalous regions of zero or negative expansion, whereas the thermal expansion of Nb2O5 ceramics decreases in magnitude in the region of negative values, and their thermal expansion curve becomes more symmetrical.

Effect of growth conditions on the domain structure of LiNbO3〈Gd〉 single crystals

The domain structure of LiNbO3〈Gd〉 single crystals grown under steady-and unsteady-state conditions has been studied using Thixomet, a high-speed, flexible image analysis system. The results have been used to formulate the growth conditions of (1) doped lithium niobate single crystals with a modulated dopant distribution and, accordingly, a regular domain structure, whose period is determined by the ratio of the pull rate to the crystal rotation rate, and (2) doped lithium niobate single crystals with a sufficiently uniform dopant distribution along the growth direction, without any regular domain structure.

Synthesis, structure, and electrical and mechanical properties of Nb2(1 − y)Ta2y O5 ceramics

The structural, mechanical, and electrical properties of ceramics based on coprecipitated Nb2(1 − y)Ta2yO5 pentoxides have been studied by scanning probe microscopy, Raman spectroscopy, and impedance spectroscopy. We have examined the effect of high-intensity light processing on the structure and properties of the Nb2(1 − y)Ta2yO5 ceramics.

Effect of ceramic powder particle size on the electrical properties of Li0.03Na0.97Ta0.05Nb0.95O3 ceramics

We compare the microstructure, electrical properties, and Raman spectra of ceramic samples of the Li0.03Na0.97Ta0.05Nb0.95O3 ferroelectric solid solution prepared by a conventional ceramic processing technique using ceramic powders with different particle sizes. The Li0.03Na0.97Ta0.05Nb0.95O3 solid solutions prepared from the powders of different particle sizes are shown to differ only slightly in average grain size, pore size, and porosity, but the particle size of the ceramic powder has a significant effect on their electrical properties. The difference in properties between the samples is due not so much to the difference in particle size between the parent ceramic powders as to the fact that the diffusion processes involved in solid-state synthesis may give rise to composition gradients, and grains that differ in size may differ in microstructure and composition.

Formation of a stoichiometric layer and new polar phase upon exposure of LiTaO3 single crystals to lithium vapor

We present evidence that vapor transport equilibration (VTE) of lithium tantalate crystals in lithium vapor produces layers tens to hundreds of microns thick which differ in phase composition and stoichiometry. Stoichiometric layers, up to 500 μm in thickness, have a coercive field tens of times lower than that in congruent lithium tantalate single crystals, which makes them suitable for producing regular domain structures that can be used in the fabrication of integrated optic devices: optical converters and minilasers. After VTE processing, a thin (within 30 μm) surface layer of single-crystal lithium tantalate has a new, polar (ferroelectric) structure with a phase transition temperature of ∼120°C.

Microstructures and nanostructures, elastic properties, and heat resistance of ceramics with a protective coating based on niobium pentoxide exposed to a concentrated light flux

The effect of exposure to a concentrated light flux on the structure, elastic properties, and thermal expansion of ceramic niobium pentoxide has been investigated. The heat resistance of the products obtained from layered ceramics with coatings based on niobium pentoxide has been estimated.