Anđelka Tonejc

Revised and new crystal data for indium selenides

A redetermination of crystal data for InSe (hexagonal), α-In2Se3 (rhombohedral), α-In2Se3 (hexagonal), β-In2Se3 (rhombohedral), γ-In2Se3 (hexagonal), and δ-In2Se3 (hexagonal) has been undertaken because of discrepancies among the published results in the literature and in the JCPDS Powder Diffraction File.

An analysis of evolution of grain size-lattice parameters dependence in nanocrystalline TiO2 anatase

Abstract Due to the specific properties of nanocrystalline materials in comparison with crystalline materials, it is essential to investigate their structural parameters like lattice parameters and grain sizes. We used the Rietveld method and refined electron powder data (recorded with selected area electron diffraction—SAED) on nanocrystalline (nc) TiO2-anatase prepared by sol–gel route. We correlated refined lattice parameters with average grain size obtained from transmission electron microscopy (TEM) images. We give preliminary results on relative changes of lattice parameters a and c vs. the mean grain size in nc TiO2-anatase.

Evidence from HRTEM image processing, XRD and EDS on nanocrystalline iron-doped titanium oxide powders

We investigated nanosized iron-doped TiO2 in the presence of poly(ethylene glycol) (PEG), synthesised by modified sol–gel method, by transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution electron microscopy (HRTEM), HRTEM image processing, energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). XRD of as prepared sample showed very broad diffraction maxima of anatase as the dominant phase and an additional maxima ascribed to PEG. The SAED pattern reveals nanocrystalline rings of anatase whereas PEG was barely observed. The presence of PEG in HRTEM image was not observed, while in the Fourier transforms (FT) of HRTEM images the PEG spots were indexed. The Fourier filtered images reveal lattice images of PEG and anatase that constitute the observed grain. The elongation of unit-cell parameter c was found and ascribed to infiltration of PEG and iron into TiO2 anatase lattice. XRD pattern of annealed sample showed again that the anatase is the dominant phase, but the faint lines of rutile and brookite were also detected. PEG was not observed. However, SAED patterns and FT of HRTEM images revealed the Fe2O3 maghemite-q that precipitated during thermal treatment of the as-prepared sample. In both samples, in as-prepared and in annealed, an amorphous phase was observed and its amount determined from HRTEM images.

Determination of the monoclinic, tetragonal and cubic phases in mechanically alloyed ZrO2-Y2O3 and ZrO2-CoO powder mixtures by Raman spectroscopy

Abstracts are not published in this journal

Transmission electron microscopy studies of nanophase TiO2

Abstract The chemical and microstructural properties of nanosized TiO 2 , obtained by sol—gel procedure, were investigated. The samples were characterized by analytical electron microscopy combining electron diffraction, high resolution electron microscopy and atomic force microscopy. These methods were supported by X-ray diffraction and thermal analysis. The chemical and structural properties, as well as the size of grains, depended on the temperature of TiO 2 preparation. In the temperature range between 293 and 820 K the TiO 2 grains consisted of anatase, as the dominant phase, and brookite. High resolution electron microscopy showed that the sample heated at 573 K had grain sizes from 2 to 10 nm, the average being (5 ± 1) nm, and the pore sizes from 4.5 to 12 nm. The sample heated at820 K revealed larger grain sizes, from 7 to 12 nm, the average being (9 ± 1) nm, and the pore sizes from 6 to 10 nm. These values were confirmed by X-ray diffraction broadening.

PbCO3·2PbO+Ag2O and PbCO3·PbO+Ag2O (PACO) systems: route for novel superconductors

Abstract We have investigated powdered mixtures PbCO 3 ·2PbO+Ag 2 O and PbCO 3 ·PbO+Ag 2 O prefired in CO 2 and annealed in CO 2 +O 2 atmosphere. The samples exhibit resistive properties characteristic for superconductivity exceeding room temperature.

Phases, lattice parameters and thermal expansion of (GaxIn1−x)2Se3, 1≥x≥0, between room temperature and melting point

The phases, their lattice parameters and the linear coefficient of the lattice thermal expansion were determined by high-temperature X-ray diffraction between room temperature and the melting point for the system (GaxIn1 − x)2Se3 (1 ≥ x ≥ 0). A wide homogeneity range of zinc blende structure was found in the Ga-rich region when a certain critical temperature was reached. In the In-rich region the alloys were isostructural with γ-In2Se3 at all temperatures, and the linear thermal-expansion coefficient was composition dependent.

HREM, TEM and XRD observation of nanocrystalline phases in TiO2 obtained by the sol-gel method

Abstract The microstructural and chemical properties of nanosized TiO 2 , obtained by the sol-gel procedure, were investigated. The specific surface area of TiO 2 was dependent on modifications of the general sol-gel procedure. A gradual decrease of the specific surface area (BET) from 169.9 to 2.7 m 2 g −1 with an increase of the calcination temperature up to 983 K was observed. At 913 K rutile was observed, together with a small amount of anatase. The grain size of the anatase phase changed from 4.5 ± 2 nm to 6.5 ± 2 nm when the temperature increased up to 913 K. The high specific surface area, small grain size, adequate porosity, and favorable phase composition of nanosized TiO 2 , synthesized in the present work, rendered this material suitable as photoelectrode in dye-sensitized solar cells.

Possible RT superconductivity from Pb3CO5-Ag2O (PACO) system

Abstract Some interesting results that could be eventually explained as coming from superconductivity (SC) in Pb 3 CO 5 -Ag 2 O (PACO) system are reported. Samples prepared at 340–350 °C in combined CO 2 -O 2 atmosphere exhibit low resistance states at room temperature (RT) with resistivity three orders of magnitude lower than that of silver. In addition, characteristic threshold current density dependence of electric resistance together with the DC susceptibility data obtained on balance support the idea of superconductivity in PACO system.

Determination of Nanosize Particle Distribution by Low Frequency Raman Scattering: Comparison to Electron Microscopy

The methodology for the determination of a nanosized particle distribution by low frequency Raman spectroscopy is described. It is based on a ν -1 dependence of the Raman light of the vibration coupling coefficient C(ν) and on the fact that each nanocrystalite of diameter D vibrates with its eigenfrequency i α 1/D. The effect of the particle vibrational lifetime on the shape of the distribution is analyzed and found to be negligible for free TiO2 nanoparticles. The size distributions of TiO2 nanoparticles estimated by Raman spectroscopy were compared to those obtained by transmission electron microscopy including dark field and high resolution imaging. The Raman spectroscopy was shown to be a simple, fast method that has favourable statistics due to a macroscopic probe volume and makes in situ measurements possible.