T. I. Milenov

Glass formation in the CaO-Bi2O3-B2O3 and SrO-Bi2O3-B2O3 systems

A physicochemical study of glasses based on the MO-Bi2O3-B2O3 and SrO-Bi2O3-B2O3 systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.

Growth and characterization of large La1-xPbxMnO3-δ crystals

Abstract The experiments on crystal growth of Ln1−xPbxMnO3−δ (LPMO) (x=0.25) were carried out by the high temperature solution growth method. The larger crystals (≥1 cm3) with an almost constant composition were grown at cooling rate 0.5 K h−1 and LPMO: flux=1:5 ratio. The obtained crystals were examined by the scanning electron microscopy and the X-ray diffraction methods. It was established by the X-ray double crystal rocking curve analysis and topography that the larger crystals, adhered to the bottom of the crucible with large contact area were strained. The subgrain structure as well as growth bands and dislocations are often observed in such crystals. The low structural quality of these crystals was confirmed by measuring of the magnetic susceptibility.

X-ray diffraction topography investigation of the core in Bi12SiO20 crystals

Abstract The core in a large Bi 12 SiO 20 crystal as well as the regions free of optical inhomogenities was examined by X-ray double-crystal diffraction topography. It was established that the observed defects in the central core are two-dimensional. The absorption of some impurities as well as the composition changes observed in this area by other authors, should be considered as a consequence of the formation of these defects.

Effect of Eu 2 O 3 Doping on the Crystallization Behavior of BaO-Bi 2 O 3 -B 2 O 3 Glasses

We gave studied the crystallization behavior of 30BaO · 25Bi2O3 · 45B2O3 glasses doped with Eu2O3 to different levels. At a Eu2O3 content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.

Crystal structure of Bi36MgP2O60 − δ

A compound with the general formula Bi36MgP2O60 − δ was obtained by a solid-state reaction method. Its composition was confirmed using EDAX. The compound belongs to the cubic crystal system (space group I23, no. 197) and has a sillenite-type structure. The lattice parameter ao is 10.15704(12) Å. The Rietveld refinement of the crystallographic data revealed mixed tetrahedral sites (2a) occupied by Mg, P, and Bi in a ratio of 32: 63: 5. The resulting lattice strains are compensated by vacancies in the cationic (2a) and anionic sites (24f) and by distortion of the Bi-O framework detected by IR and Raman spectroscopy.

Deformational twinning in CdTe crystals grown by the Bridgman method

Abstract The results of the crystal growth of cadmium telluride (CdTe) crystals by the Bridgman method are reported in the present work. A stoichiometric ratio of cadmium and tellurium in the melt as well as cadmium- and tellurium-rich melts are used in the different crystal growth experiments by the Bridgman method. The obtained large ( φ 54 mm) crystals are plastically deformed. They were examined by X-ray diffraction methods. The conclusion that some of the twins in the melt grown CdTe crystals at high temperatures are due to the thermal stress is made according to the experimental findings. Some results concerning the influence of the {111}-{111} twin boundaries on the resistivity as well as the counting of low energy gamma rays characteristics are presented here also. The worsened resistivity and parameters in counting of 241 Am source γ-rays are explained by the presence of structural defects in the solid state γ-ray counters.

Effect of rapid thermal annealing on the properties of thin carbon films

Carbon films deposited on silicon substrates were studied after rapid thermal annealing (RTA) by Raman spectroscopy and electrical resistance measurements. The temperature and duration of RTA are related to the form and shift of the peaks in the Raman spectra and resistance curve of the films.

Optical and vibrational spectra of Bi 1.8 Fe 1.2(1 – x ) Ga 1.2 x SbO 7 solid solutions with pyrochlore-type structure

Optical and vibrational spectra of Bi1.8Fe1.2(1 – x)Ga1.2xSbO7 solid solutions with pyrochlore structure have been studied. It has been shown that the compounds have strongly disordered structure. It has been established that a decrease in iron content causes a marked shift of Bi1.8Fe1.2(1 – x)Ga1.2xSbO7 absorption edge. According to assessment of band gap width, Bi1.8Ga1.2SbO7 is the most wide-band compound (2.90 eV), while Bi1.8Fe1.2SbO7 is the most narrow-band compound (1.88 eV).

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C60 and C70 fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp2 bond hybridization under hydrothermal conditions was proposed.

Growth, composition and dielectric properties of Pb3Ni1.5Mn5.5O15 single crystal

Single crystals of Pb3Ni1.5Mn5.5O15 were successfully grown by the high temperature solution growth method. Their composition was determined by energy dispersive X-ray analysis. The phase homogeneity of the grown crystals was examined and confirmed by powder X-ray phase analysis. The structure was characterized by X-ray single crystal diffractometry and was indexed in the trigonal space group P-3c1 (No. 165) with lattice parameters a = 9.9142(2) A and c = 13.4923(18) A. The dielectric properties of Pb3Ni1.4Mn5.6O15 were investigated in the temperature range 150 – 500 K. The AC -measurements were carried out for 3 different frequencies: 10 kHz, 100 kHz and 1 MHz. From the DC measurements thermal activation energy was estimated.