Volume 7, Issue 2

Various compositions (1−x)BaTiO3 + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba1−x Pbx (Ti1−x Lix ) O3−3x F3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 107 Hz). The dielectric performances are the best for ceramic Ba0.97Pb0.03(Ti0.97Li0.03)O2.91F0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.

The effect of calcium substitution on the afterglow of tetrastrontium aluminate phosphors (Sr4Al14O25:Eu2+, Dy3+) was investigated. A series of (Sr1-xCax)O⊎nAl2O3:Eu2+(1%), Dy3+(0.5%), with variation of calcium content (x = 0 − 1), were synthesized by a high temperature solid state reaction in a reducing atmosphere. The photoluminescence, persistent luminescence (afterglow), and lumen equivalents of these materials were studied and compared. It turned out that the afterglow properties of the phosphors were strongly dependent on the Sr/Ca ratio. As the Ca content increased, a phase transition and blue shift in emission spectra were observed.

The purpose of this work was to find and investigate a correlation between the carbonate ion content in crystalline lattice and defect structure, and solubility of the materials; finally, to prepare the materials under study for in vitro tests. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO2, BET adsorption, were applied to determine the efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution,. It was shown that AB-type substitution prevails over other types with the carbonate content increase. According to in vitro tests, the bioactivity of the samples is correlated with the carbonate content in carbonate-doped hydroxyapatite due to accumulation of defects in carbonated hydroxyapatite nanocrystals.

Investigation of the magnetic properties of MnGaN epitaxial layers as a function of external electrical field was performed on the basis of field effect structure. The structure included substrate of n-type GaN, epitaxial layer of n-type MnxGa1-xN, dielectric layer and metal layer acting as field effect device gate. Each Mn atom in MnxGa1-xN contributes 4 net spins due to the electrons occupying energy levels 4F, 4D, 4P and 4G belonging to 3d orbital, and these levels are in the energy band gap and in the top of the valence band of MnxGa1-xN. The position of the Fermi level is determined to be in the energy band gap of the layer of GaN and to be above the level 4F in the layer of MnxGa1-xN. In this way application of external negative voltage on the gate causes change in the number of electrons contributing net spins and the saturation magnetization Msat of MnxGa1-xN changes as well. It was found that Msat changes in the range 1.15 × 10−3–0.7 × 10−3 A μm−1 if the external voltage changes in the interval 0–−5V. The application of this structure for the design of spintronic devices is discussed in this paper.

In the work presented here, the way of obtaining the phase with general formula Co3+1.5xCr2–x(VO4)4 (0 ≤ × 4 - Co3V2O8 that is formed in one of the intersection of the ternary CoO - V2O5 - Cr2O3 system. Monophasic Co3Cr2(VO4)4 (Co3+1.5xCr2−x(VO4)4, where × = 0) was obtained from both a mixture comprising CrVO4 and Co3V2O8 as well as from the mixture of CoV2O6 with CoCr2O4. The Co3+1.5xCr2−x(VO4)4 is isotypic with the those demonstrating the lyonsite-type structure. The temperature of melting for the new compound was established using the DTA methods.

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH4)2HPO4 and Ca(NO3)2, or CaCl2 or Ca(CH3COO)2 with [Ca2+]/[PO 43−] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO3)2/(NH4)2HPO4, CaCl2/(NH4)2HPO4, Ca(CH3COO)2/(NH4)2HPO4 gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH4NO3, NH4Cl, NH4CH3COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO3)2/(NH4)2HPO4 consisted of β-Ca2P2O7, whereas the samples based on the powders derived from CaCl2/(NH4)2HPO4 were composed of β-Ca2P2O7 and β-Ca3(PO4)2, and the samples based on the powders synthesized from Ca(CH3COO)2/(NH4)2HPO4 contained only β-Ca3(PO4)2. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.

Phase relations up to the solidus line in part of the Sb-Zn-O system have been investigated over the entire concentration range of the α-Sb2O4-ZnO system in air ( \( P_{O_2 } \) = 0.21 atm) using XRD and DTA/TG. The components of this system in air form ZnSb2O6 and Zn7Sb2O12. The results allow division of the system into three subsystems, i.e. α-Sb2O4-ZnSb2O6; ZnSb2O6Zn7Sb2O12 and Zn7Sb2O12-ZnO. The temperature ranges over which the ZnSb2O6 and Zn7Sb2O12 remain at equilibrium with other solid compounds depend on the gaseous atmosphere.

In this paper we present the methods to chemically synthesize the Sb2Se3 nanorods and study the electrical and optical properties of a single Sb2Se3 nanorod with an average size of 70 nm in diameter and a length of about 1 μm to 2 μm. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (∼ 1 mm) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb2Se3 nanorod.

Kinetic studies were performed on two types of leucite precursors. These precursors were prepared using a hydrothermal method at 150°C; the reaction time was 1.5 hours. In order to obtain precursors having different amounts of seed the molarity of KOH was changed. These intermediate products were subsequently calcinated from 5 minutes to 72 hours at temperatures of 850°C, 900°C, 950°C, 1000°C and 1050°C. The crystallinities of the powders were calculated by X-ray diffraction analysis. The crystallization curves for the synthesis of leucite exhibited a typical sigmoidal characteristic. Using different kinetic equations it was found that the Avrami-Eroféev model is the most appropriate to describe the experimental data. Using the Avrami-Eroféev model n reaches an average value of 2.9 which is connected with the three-dimensional growth of nuclei. The calculated activation energy of crystallization of leucite was 385 kJ mol-1 for non-seeded precursors and 246 kJ mol-1 for seeded precursors, respectively.

A four-spin system with s=1 and the single-ion anisotropy, D∑ j [s jz ] 2 , is considered. When D≠0 the Hamiltonian of the system does not commute with S 2 and, therefore, S cannot be used as an additional label of energy levels. In this work we concentrate on the problem of mixing states with different total spins S. The Hamiltonian matrix is transformed to the symmetry-adapted basis (with subspaces labeled by the irreducible representations of the symmetry group) and next, after solving the eigenproblem for S 2, to the basis with vectors labeled by S. Each eigenproblem is solved exactly (at least numerically) and the eigenstates are expressed as ∑S a S ¦S〉. The coefficients aS are analyzed, especially for their D-dependence. Even in such a small system different schemes of level mixing can be observed.

PbS nanocrystals using surfactant assisted mechanochemical route has been successfully prepared. The methods of XRD, SEM, surface area and particle size measurements were used for nanocrystals characterization. The XRD patterns confirmed the presence of galena PbS (JCPDS 5–592) whatever treatment conditions were applied. The strong observable peaks indicate the highly crystalline nature in formation of PbS nanostructures where preferential crystal growth in the (200) direction after chelating agent (EDTANa2•2H2O) addition has been observed. The mean volume weighted crystallite size 4.9 nm and 35 nm has been calculated from XRD data using Williamson-Hall method for PbS synthesized without and/or with chelating agent, respectively corresponding with surface weighted crystallites sizes of 2.9 and 18.8 nm. The sample prepared without surfactant yields the smaller crystallites and the higher microstrain compared with surfactant assisted synthesis. The obtained results illustrate a possibility to manipulate crystal morphology by combining effect of milling and surfactant application.

The IR spectrum of V4Nb18O55 has been compared with the IR spectra of selected niobates of known structures to show structural relations between these compounds. This comparison shows that V4Nb18O55 has crystal structure related to T-Nb2O5, W16Nb18O94 and Ba2NaNb5O15. On the other hand, reaction between V2O5 and H-Nb2O5 yields a solid solution of V2O5 in VNb9O25. It has been proposed two models of synthesized solid solution with formulas V1+xNb9-xO25 or V1+xNb9O25+5x/2.Independently of Nb2O5 polymorph, used for synthesis, the metastable compound VNbO5 cannot be synthesized in the solid state below 650°C

Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like phases after soaking in SBF.

Studies of dissociative reduction processes of electrochromic WO3−x films were conducted to: (i) evaluate their utility for electroetching and (ii) determine their fundamental mechanistic features to reduce or eliminate their occurrence in normal optical switching and modulation operation of WO3−x films. We have found that while the small intercalating cations stabilize WO3−x structure, the large nonintercalating surfactant cations (Et4N+, CtMe3N+) contribute to the dissociative reduction. While these cations do not affect WO3−x structure of anodically protected films (E > 0.2 V), they cause surface lattice polarization on electron injection to the conduction band of WO3−x at lower electrode potentials, in the absence of intercalating cations. We have found that this process is limited to the surface and no structural damage occurs to the underlying film. The mechanistic aspects of the process have been discussed on the basis of experimental voltammetric and electrochemical quartz crystal nanogravimetric (EQCN) measurements and ab initio quantum mechanical calculations.

The present work was undertaken to investigate the bioactivity and cytotoxicity of fluorhydroxyapatite ceramics. The bioactivity was evaluated by in vitro testing in simulated body fluid (SBF), in which ion concentrations are almost identical with inorganic ion concentrations of human blood plasma. Pellets of FA, HA and FHA were immersed in SBF for 48 hours, 1 week and 4 weeks at 36.5°C. Changes of the surface microstructure of the samples were observed by scanning electron microscopy (SEM). 48 hours and one week immersion in SBF did not result in any substantial progress in bioactivity. After 4 weeks in SBF a new biologically active layer was created on the surface of the biomaterials. In addition, the embryonal mouse fibroblast cell line NIH-3T3 was used for a comparative study of basal cytotoxicity of FHA, HA and FA discs. The sensitivity of these cells for tested biomaterials was evaluated on the basis of two cytotoxic end points: cell proliferation and cell morphology. The basal cytotoxicity of FHA, FA and HA discs was measured by a direct contact method. After 24, 48 and 72 hours, the cell growth was evaluated by direct counting of non-affected cells and cells treated by biomaterials. After 72 hours of biomaterials treatment, about 25% inhibition of cell number and unchanged morphology was found.

Phase diagrams in the subsolidus area of the systems FeVO4 - CdO and FeVO4 - Cd2V2O7 have been deduced using the results of XRD and DTA analyses. On the basis of these diagrams and some additional verifying research, a projection of the subsolidus area of the CdO - V2O5 - Fe2O3 system onto the plane that comprises the components’ concentration triangle has been presented. The H-type phase is the only phase formed in this system. It co-exists at equilibrium with other phases in six subsidiary subsystems.

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by the homogenous hydrolysis of TiOSO4 in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and Nitrogen adsorption-desorption was used for surface area (BET) and porosity determination (BJH). The photocatalytic activity of the Ru-doped titania samples were determined by photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 nm and 400 nm wavelengths.