Synthesis of lead magnesium niobate and La-modified lead magnesium niobate using different Mg precursors

Summary In the present study, the effect of the partial replacement of Pb²⁺ by La³⁺ in the lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ (PMN) perovskite structure was examined, taking into account the Mg-source. Pure lead magnesium niobate (PMN) and lanthanum-modified lead magnesium niobate (PLMN) having composition (Pb_1-xLa_x) (Mg_1+x/3Nb_2-x/3)O₃ with x=0.2 were elaborated. The phase formation was investigated by DTA/TG methods correlated with X-ray diffraction, performed on materials obtained in non-isothermal conditions. The diffraction data for the ceramics obtained by isothermal treatments emphasized the influence of the lanthanum on the crystal structure, inducing the doubling of the unit cell parameter. SEM investigations pointed out the lanthanum inhibitor effect on the grain growth process, leading to an uniform grain distribution.     

Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis,mesomorphism and emission properties

A series of flexibly linked bis(pyridinium) salts with various counterions (Br^?, PF₆^?, BF₄^? and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col_h) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.     

Phase Formation Study of Alkaline Earth-doped Lanthanum Chromites

In this paper the influence of alkaline-earth admixtures on the synthesis of lanthanum chromites of La_1–xM_xCrO₃ (x=0; 0.3; M=Ca, Sr, Ca+Sr) type was studied. The formation mechanism as well as the phase composition evolution, under non-isothermal and isothermal conditions, were investigated by thermal analysis and X-ray diffraction. The structure of the compounds and of the solid solutions formed depends on the solute type by means of the structural distortion induced. The crystallinity of the chromites obtained is obviously influenced by both the temperature and the thermal treatment plateau. This revised version was published online in August 2006 with corrections to the Cover Date.     

PLD and RF-PLD synthesis of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films for electrically controlled devices

Ba_0.6Sr_0.4TiO₃ (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.     

Thermal analysis,microstructure and impurity phases evolution in Fe14Cr ferritic steel powders ball-milled in air and under an argon atmosphere

Journal of Thermal Analysis and Calorimetry - Azobenzenes undergo reversible trans–cis photo-isomerization and have been studied extensively as photo-responsive materials. Despite their...     

Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings

Bio-glass films were deposited by radio-frequency magnetron sputtering technique onto medical grade Ti6Al7Nb alloy substrates from prepared silica based bio-glass target. A low deposition temperature was used (150 °C) and three different working pressures, followed by annealing in air at 550 and 750 °C. A quasi-stoichiometric target to substrate atomic transfer was found for Si, Ca and P, along with strong enrichment in Na and depletion in K and Mg, as evidenced by the energy dispersive microanalysis. The best results, taking into account stoichiometry and surface roughness, were obtained for the BG layers deposited at 0.3 Pa argon working pressure. The infrared spectroscopy of the as-sputtered and of the annealed films evidenced the characteristic molecular vibrations of silicate, phosphate and carbonate functional groups. The as-deposited films are amorphous and became partly crystalline after annealing at 750 °C, as evidenced by X-ray diffraction. The pull-out measurements, performed with a certified pull-test machine, gave very strong film–substrate adhesion strength values. For the non-crystalline layers, the pull-out strength is higher than 85 MPa, and decreases after annealing at 750 °C to 72.9 ± 7.1 MPa. The main objective of this work was to establish the influence of the working pressure upon the composition and morphology of the as-deposited films, and of the annealing temperature upon structure and film–substrate adhesion.     

Phase Formation Study of The Substituted Lanthanum Manganites Solid Solutions

It is well known that the manganites-based solid solutions are interesting for their electric and magnetic properties. LaMnO₃ exhibits a distorted perovskite structure due to Mn³⁺ ion, which determines the presence of the Jahn–Teller effect. Replacing La³⁺ host ions by cations of lower valence leads to the disappearance of this effect and changes the characteristics of these materials. Although the formation of manganites-based solid solutions has been intensively studied, there are some unelucidated aspects concerning their formation mechanism, depending both on the precursors used and on the thermal treatment applied in order to obtain suitable properties. In this work the formation mechanism of La_0.7M_0.3MnO₃ (M=Ca, Sr, Ca+Sr in equimolecular mixture) solid solutions, in isothermal and non-isothermal conditions, was studied. For this purpose XRD, DTA/TG and spectral techniques were used. The solid solutions formation was found to be more dependent on the Mn-precursors type than the thermal treatment conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sintered and 3D-Printed Bulks of MgB2-Based Materials with Antimicrobial Properties

Pristine high-density bulk disks of MgB₂ with added hexagonal BN (10 wt.%) were prepared using spark plasma sintering. The BN-added samples are machinable by chipping them into desired geometries. Complex shapes of different sizes can also be obtained by the 3D printing of polylactic acid filaments embedded with MgB₂ powder particles (10 wt.%). Our present work aims to assess antimicrobial activity quantified as viable cells (CFU/mL) vs. time of sintered and 3D-printed materials. In vitro antimicrobial tests were performed against the bacterial strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Enterococcus faecium DSM 13590, and Enterococcus faecalis ATCC 29212; and the yeast strain Candida parapsilosis ATCC 22019. The antimicrobial effects were found to depend on the tested samples and microbes, with E. faecium being the most resistant and E. coli the most susceptible.     

Thermal analysis and microstructure of oxide dispersion strengthened ferritic steels produced by ball milling with different amounts of process control agent

Journal of Thermal Analysis and Calorimetry - Fe–14Cr–3&nbsp;W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of elemental powders with...     

Formation and properties of some Nb-doped SrTiO3-based solid solutions

It is well known that SrTiO₃ is one of the widely used materials in the electronic ceramic industry. Donor-type dopants are often added in order to improve the electrical properties of SrTiO₃-based ceramics. In the present study, the formation and characteristics of undoped and Nb-doped SrTiO₃ were studied as a function of both the niobium dopant concentration and the Sr/Ti ratio (at the same Nb content). The formation mechanism of the mixed Sr(Ti,Nb)O₃ crystals was investigated by XRD and thermal analysis. The niobium solubility in the SrTiO₃ perovskite lattice was estimated by means of unit cell parameter data. The influence of Sr concentration on the microstructure of the ceramics obtained was investigated by SEM. Ceramic properties pointed out the influence of the dopant concentration and stoichiometry on the sintering behavior of these materials. This revised version was published online in July 2006 with corrections to the Cover Date.