Phase composition of Bi2O3 specimens doped with Ti, Zr and Hf

Powder mixtures of α-Bi2O3 containing 2, 5 and 10 mole % of TiO2, ZrO2 or HfO2 were homogenized, heated at 820ºC for 24 h and quenched in air. X-ray powder diffraction technique was used to characterize the prepared samples. In all cases metastable Bi2O3 polymorphs, γ-Bi2O3 or β-Bi2O3, are found as single or major phases. Addition of Ti4+ ions stabilizes γ-Bi2O3 polymorph, while either Zr4+ or Hf4+ ions stabilize β-Bi2O3 polymorph. In the samples with 2 and 5 mole % of TiO2 the presence of even two γ-Bi2O3 phases (Bi12TiO20 compound and a very low Ti-doped γ-Bi2O3) was established. Similarly, in the sample with 2 mole % of HfO2 two β-Bi2O3 phases were found. Phase composition of prepared samples, values of unit cell parameters and the appearance of two polymorphs with identical crystal structure but different unit cell parameters are discussed and compared with known data

Characterization of Barium Titanate Ceramics by Impedance Spectroscopy

Poster presented at the 9th Conference of the Yugoslav Materials Research Society - YUCOMAT 2007, Herceg Novi, Crna Gora, 10-14. septembar 2007

Extremal problems of brownian motion and other random processes

Neka je M maksimum i neka je N minimum negativnog martingala X1, X2, . . . , Xn...Let M be a maximum and let N be a minimum of the non-negative martingale X1, X2, . . . , Xn..

Mechanochemical synthesis and electrical conductivity of nanocrystalline δ-Bi2O3 stabilized by HfO2 and ZrO2

A powder mixture of α-Bi2O3 and HfO2, in the molar ratio 2:3, was mechanochemically treated in a planetary ball mill under air, using zirconium oxide vials and balls as the milling medium. After 50 h of milling, the mechanochemical reaction led to the formation of a nanocrystalline δ-Bi2O3 phase (fluorite-type solid solution Bi0.78Hf0.59Zr0.63O3.61), with a crystallite size of 20 nm. The mechanochemical reaction started at a very beginning of milling accompanied by an accumulation of ZrO2 arising from the milling tools. The samples prepared after various milling times were characterized by X-ray powder diffraction and DSC analysis. The electrical properties of the as-milled and pressed Bi0.78Hf0.59Zr0.63O3.61 powder were studied using impedance spectroscopy in the temperature range from 100 to 700°C under air. The electrical conductivity was determined to be 9.43×10-6 and 0.080 S cm-1 for the temperatures of 300 and 700°C, respectively.Smeša prahova α-Bi2O3 i HfO2 u molarnom odnosu 2:3 mehanohemijski je tretirana u planetarnom mlinu u atmosferi vazduha, koristeći cirkonijumske posude i kuglice kao medijum za mlevenje. Posle 50 h mlevenja, mehanohemijska reakcija dovodi do stvaranja nanokristalne δ-Bi2O3 faze (čvrsti rastvor fluoritske strukture Bi0,78Hf0,59Zr0,63O3,61), veličine kristalita 20 nm. Mehanohemijska reakcija otpočinje u samom početku mlevenja i praćena je akumulacijum ZrO2 koji potiče od medijuma za mlevenje. Uzorci dobijeni posle različitih vremena mlevenja karakterisani su rendgenskom strukturnom i termijskom analizom. Električna svojstva mlevenih i presovanih Bi0,78Hf0,59Zr0,63O3,61 prahova ispitivana su impedansnom spektroskopijom u temperaturnom opsegu od 100 do 700°C. Dobijena električna provodnost je 9,43·10-6 i 0,080 S cm-1 za temperaturu 300 i 700°C, redom

Uticaj parametara mlevenja na odnos amorfne i kristalne faze u jedinjenju Bi4Ti3O12

Poster presented at the XLVI Savetovanje srpskog hemijskog društva, Beograd, 29. mart (21. februar) 200

Characterization of nanostructured spinel NiFe2O4 obtained by soft mechanochemical synthesis

Powdery nickel ferrite, NiFe2O4 has been obtained by soft mechanochemical synthesis in a planetary ball mill. Ni(OH)2 and Fe(OH)3 are used as initial compounds. This mixture was mechanically activated for 25h, uniaxial pressed and sintered at 1100°C for 2h. The phase composition of the sintered sample was analyzed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. Morphologies were examined by scanning electron microscopy (SEM). The electrical DC/resistivity/conductivity at different temperatures was measured using a Source Meter Keithley 2410. An Impedance/Gain-Phase Analyzer (HP-4194) was used to measure the impedance spectra (100Hz - 10MHz) at different temperatures. [Projekat Ministarstva nauke Republike Srbije, br. III 45003 i br. III 45015

Enhanced high-temperature electrical response of hydroxyapatite upon grain size refinement

Correlation between high-temperature electrical response and microstructural properties of dense hydroxyapatite with average grain size from micrometer to nanometer level in heating/cooling cycle was investigated. Grain interior and grain boundary contributions to overall conductivity were determined. Nanostructured hydroxyapatite exhibited enhanced grain interior conductivity, with significantly higher activation energy (∼2.4 eV) than that of coarsed microstructures (∼1.7 eV). This difference in activation energies is explained by the possible influence of dehydroxylation during materials fabrication procedure, which affected the amount of OH- ions as the main charge carriers. Grain boundary conductivity was similar for all microstructures, with activation energy above ∼2 eV, implying the OH- ions migration across grain boundaries. Electrical response in cooling cycle confirmed the trends found during heating. © 2014 Elsevier B.V. All rights reserved

Tailoring of K0.8Al0.7Fe0.15Si2.25O6 Leucite Based Dental Ceramic Material

Potassium based ceramic materials composed from leucite in which 5 % of Al is exchanged with Fe and 4 % of hematite was synthesized by mechanochemical homogenization and annealing of K2O-SiO2-Al2O3-Fe2O3 mixtures. Synthesized material was characterized by X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (SEM/EDX). The two methods are in good agreement in regard to the specimen chemical composition suggesting that a leucite chemical formula is K0.8Al0.7Fe0.15Si2.25O6. Rietveld structure refinement results reveal that about 20 % of vacancies exist in the position of K atoms. This work is licensed under a Creative Commons Attribution 4.0 International License

Structural and magnetic properties of mechanochemically synthesized LaFe1-xCrxO3 (x = 0.5 and 0.75)

Perovskite oxides with the composition LaFe1-xCrxO3 (x = 0.5 and 0.75) have been studied. The samples have been prepared using the mechanochemical treatment. A mixture of crystalline La(OH)3, Fe2O3 and Cr2O3 powders in stoichiometric ratio was mechanochemically treated in a planetary ball mill up to 40 h of milling. The mechanochemical formation of the LaFe1-xCrxO3 perovskite phase was followed by X-ray diffraction and magnetization measurements. The Rietveld refinement of the XRD data shows that the compounds crystallize in an orthorhombic perovskite structure with a random distribution of the Fe and Cr cations at the B sublattice. All structural and microstructural parameters were analyzed. In addition, magnetic measurements for LaFe0.5Cr0.5O3 show clear antiferromagnetic ordering bellow 250 K, which supports above conclusion of random distribution of Fe and Cr cations

Biodiesel synthesis based on CaO·ZnO.K2CO3 as catalyst

The mixed oxide of CaO·ZnO and K2CO3 were prepared by ball milling of CaO and ZnO powders and water, with addition of K2CO3 and afterward by calcination at 700 oC. Influence of different molar ratio of K2CO3 and CaO (x=1, 2 and 4 moles of K2CO3 per 10 moles of CaO) was studied . The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and the particle size laser diffraction (PSLD) distribution. The addition of smaller amount of K2CO3 at the beginning of ball miling (x≤2), favors the formation of calcium zinc hydroxide hydrate, while it is not the case when K2CO3 larger addition was used (x > 2). A larger amount of potassium carbonate in the initial composition of powder mixture negatively affected formation of CaZn2(OH)6·2H2O. Bimodal distribution were detected for all samples after calcination at 700 oC and the results showed that the distribution of elements in the bulk is not homogeneous and that surface of formed mixed oxide CaO.ZnO (XPS analysis) after calcination is mainly covered by potassium species. That evidence indicate that the K2CO3 was not fully incorporated into the matrix. Prepared samples could be used for methanolysis of vegetable oil and fatty acid methyl esters (FAME, i.e. biodiesel) synthesis