Search

Ytterbium-doped nanocrystalline powders of yttrium aluminum garnet (YAG:Yb3+) with ytterbium content from 5 to 30 at.% have been prepared by the citrate sol–gel method. Phase composition, crystal structure and microstructure of the materials were studied by means of X-ray powder diffraction techniques using both laboratory and synchrotron radiation sources. The photoluminescence spectra and the photoluminescence decay kinetics of Yb3+ ions at room temperature were performed as well. It was revealed that materials calcined at lower (1000 °C) temperature possess a small amount of Yb3+ ions occupying the octahedral sites of Al3+ ions, whereas the materials calcined at 1200 °C form the proper (Y1−xYbx)3Al5O12 solid solution. [ABSTRACT FROM AUTHOR]

Spatial changes of optical and pyroelectric properties of doped LiNbO3 single crystals were investigated. Doping with Cu and Fe was performed after crystal growth by thermal diffusion at elevated temperatures. The crystals were all-side-covered by corresponding metal oxide powder before annealing. In order to reveal the role of various types of diffusion sources in the formation of the modified layers of LiNbO3, the same investigations were performed on the samples covered by copper films before annealing. The optical absorption spectra of the samples were recorded in a direction perpendicular to the direction of diffusion at different distances from the crystal surface. The intensities of the absorption bands of Cu+ (400 nm), Cu2+ (1000 nm) and Fe3+ (480 nm) ions were analyzed depending on the annealing temperature and the distance from the source of diffusion. The maxima were obtained on the depth profiles of additional absorption for all samples. The concentrations of Cu and Fe ions were calculated in accordance with the Smakula-Dexter formula. For the determination of correlation of the changes of optical and pyroelectric properties, the profiles of pyroelectric coefficient in the doped crystals were investigated by the laser intensity modulation method. To avoid the measurement uncertainty of thermal wave method that increases with increasing depth, the pyroelectric current was registered under excitation from both the front and the back sides of the sample. The averaged pyroelectric coefficients were also determined for calibration of the results. Here, a Peltier stage provided a sinusoidal modulation of the sample temperature at a frequency of 0.1 Hz. It is shown that diffusion doping affects the pyroelectric properties of lithium niobate crystals. [ABSTRACT FROM AUTHOR]

The paper reports a growth of the high-quality Gd3Ga5O12 (GGG) homoepitaxial films by the liquid phase epitaxy technique using the PbO-B2O3 and PbO-B2O3-V2O5 fluxes. The influence of the flux composition containing V2O5 as well as the growth temperature is discussed basing on the optical absorption and the electron probe micro analysis results. [ABSTRACT FROM AUTHOR]

Crystal structure and transport properties of the mixed praseodymium cobaltites-ferrites PrCo1-xFexO3 have been studied in the temperature range of 298-1173 K by a combination of in situ X-ray synchrotron powder diffraction and temperature dependent impedance spectroscopy measurements. In situ high temperature powder diffraction examination of PrCo1-xFexO3 series revealed considerable anomalies in the lattice expansion which are especially pronounced for the cobalt-rich specimens. These anomalies, which are reflected in a sigmoidal dependence of the unit cell dimensions and in the considerable increase of the thermal expansion coefficients, are obviously associated with transitions of Co3+ ions from low spin to the higher spin states and the coupled metal-insulator transitions, occurring in in rare earth cobaltites at the elevated temperatures. Indeed, the temperature-dependent impedance measurements clearly prove the change of conductivity type from dielectric to the metallic behaviour in the mixed cobaltite-ferrites PrCo1-xFexO3 at the elevated temperatures. [ABSTRACT FROM AUTHOR]

This paper is devoted to the use and further development of the single crystal growing technique invented by Professor Jan Czochralski (1885-1953). The possibilities of the Czochralski technique are demonstrated. Further improvements were introduced at the Scientific Research Company "Carat" (Lviv, Ukraine) to grow large size complex oxide single crystals. The paper presents an overview of some single crystals grown with the use of a modified technology. Growth parameters and properties of resulting crystals are summarized to show a high potential of the Czochralski technique as an industrial technology to grow large-size, high quality, and structurally perfect single crystals of complex oxides. [ABSTRACT FROM AUTHOR]

The analysis of cation sublattices population in magnesium doped LiNbO3 crystals is carried out. It is shown that volume concentration of lithium vacancies (VLi) monotonously increases with increasing of MgO content in the crystal up to the threshold value. A series of LiNbO3 crystals with various concentration of Mg2+ were investigated by 7Li and 93Nb Nuclear Magnetic Resonance (NMR). It is concluded that the peculiarities of NMR spectra in Mg-doped LiNbO3 crystals can be explained by the formation of defect complexes including MgLi ions and VLi on the shortest distances between them. [ABSTRACT FROM AUTHOR]