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Characteristics of phase transitions of lead barium niobate compositions around the morphotropic phase boundary were investigated. Using structural characterizations, it was found that the morphotropic phase boundary extends toward a wide composition range, in which both tetragonal (4mm) and orthorhombic (m2m) tungsten bronze phases coexist. In addition, on heating, two phase transitions were observed for all the studied compositions. First, the fraction with m2m symmetry phase transforms into the 4mm symmetry one and, second, the 4mm symmetry phase, which represents the whole material, transforms into the paraelectric phase (4/mmm symmetry). The phase transition temperatures were determined from dielectric characterizations. These results helped to improve the phase diagram of the pseudobinary PbNb2O6–BaNb2O6 system around the morphotropic phase boundary region. [ABSTRACT FROM AUTHOR]

High Curie temperature ferroelectrics are promising materials to construct transducers for high-temperature piezoelectric applications. Among them, the lead niobate system is one that displays such characteristic. In this work, the dielectric behavior of lead niobate ferroelectric ceramics was analyzed in the frequency range of 20 Hz-2 GHz. Ceramic samples with nominal formula PbNb2O6 (PN) were prepared by the solid-state reaction method. The phase transition was investigated with the Santos-Eiras’ phenomenological model. The values of the parameter, which determine the phase transition character (ξ), are close to 1, indicating a conventional ferroelectric phase transition. The PN materials showed two different dispersion processes: (1) a typical high-frequency dispersion process, which may be associated with the polar region boundaries dynamics, as observed in ferroelectric materials in the microwave frequency region, and (2) that associated with the charge carrier conduction, observed in the lowest frequencies and high-temperature region. An additional dispersion process, in the intermediate frequency range (around 2 MHz), was identified, which may be related to the overlapping between both the normal dipolar process (characteristic of the dipolar materials) and the strong low-frequency conductive process. [ABSTRACT FROM AUTHOR]

Ceramic composites based on Pb(Zr,Ti)O3/NiFe2O4 (PZT–NFO) have been synthesized from the conventional solid-state reaction method. The ferroelectric and magnetic properties have been investigated at room temperature. The obtained results revealed excellent characteristics of both ferroic responses, which suggest the studied ceramic composite as a promising material for practical applications in magneto-electric related devices. [ABSTRACT FROM AUTHOR]

In this work, the syntheses and characterization by mechanical and dielectric spectroscopies of (1-x) Bi0.5Na0.5TiO3-xBaTiO3 (BNT-100xBT), with x = 0.05, 0.06 and 0.07, lead-free piezoelectric ceramics is reported. Ceramic samples of BNT-BT have been prepared by mixed-oxide method and then conventionally sintered. X-ray diffraction patterns of sintered samples, indicated for BNT-7BT the presence of tetragonal (P4mm) complex perovskite structure, whereas for BNT-5BT and BNT-6BT the samples exhibit a mixture of tetragonal (P4mm) and rhombohedral (R3c) crystalline phases, which reveal the presence of a morphotropic phase boundary (MPB) in the BNT-BT system. Measurements of internal friction, Q-1, and the storage modulus, E', as a function of temperature at various frequencies were carried out in a Dynamic Mechanical Analyzer (DMA), in the temperature range from 0ºC to 600ºC. Dielectric profiles are recorded in the frequency range from 1kHz to 100kHz and the temperature range from room temperature to 475ºC. Mechanical loss spectra obtained for investigated compositions of BNT-BT samples showed different frequency-independent anomalies. Two main anomalies for BNT-5BT and BNT-6BT, observed around 100ºC and 430ºC were associated with the ferroelectric-antiferroelectric and antiferroelectricparaelectric phase transitions, respectively. The results obtained from mechanical loss measurements were supported by dielectric relaxation spectra. For BNT-7BT, outside the MPB, four different frequency-independent processes were observed. [ABSTRACT FROM AUTHOR]

The low-temperature sintering and electric properties of Pb0.99( Zr0.95 Ti0.05)0.98 Nb0.02 O3 ( PZTN 95/5) ferroelectric ceramics with CuO addition was investigated. The CuO addition significantly promoted the densification and reduced the sintering temperature of PZTN 95/5 ceramics by more than 200°C. The 0.2 wt% CuO-added sample sintered at 1150°C exhibited the optimum relative density of 96.7% and excellent electric properties with values of Pr = 37.80 μC/cm2, TC = 223°C, εr = 329, and tan δ = 0.016, which were superior to that of PZTN 95/5 ceramics sintered at 1350°C. [ABSTRACT FROM AUTHOR]

The article presents a study on the development of an equipment for non-destructive characterization of elastic moduli that is applicable to ceramics, concretes, and brittle materials based on American Society for Testing Materials (ASTM) standard. The study used the sonic resonance spectroscopy to measure the natural torsional and flexural vibration frequencies of the sample. The result shows that the equipment is more versatile than the current options to the measurement of the elastic moduli.

The processing of a PbNb2O6 (PN) ceramic was investigated and optimized. Through thermal gravimetric and X-ray diffraction analysis the optimal calcination condition and the starting firing temperature were estimated. The powders were submitted to thermal treatments to obtain PN ceramic powders with an orthorhombic ferroelectric phase. The effect of PbO excess addition to compensate the PbO losses, during the calcination and the firing, was also studied. The highest density value was found to be 96% of the theoretical density. The temperature dependence of the dielectric properties, for samples sintered at different temperatures, allowed the study of the sintering kinetic. [ABSTRACT FROM AUTHOR]

The FeAlO 3 phase presents an orthorhombic symmetry (Pna21 space group) with a double combination of hexagonal and cubic closed packing of oxygen ions. In this phase, there are four distorted different cationic sites, promoting piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In this work, high-energy ball milling was employed to produce the FeAlO 3 multiferroic compound. Its structural (Rietveld refinement), dielectric and magnetic properties were carefully investigated. [ABSTRACT FROM AUTHOR]

Multiferroic BiFeO 3 ceramic powders were synthesized through high-energy ball milling. The structural, microstructural and magnetic properties of the obtained samples were carefully determined. The obtained samples were very fractured and strained due to the employed milling conditions, motivating the agglomeration of the nanopowders. The unit cell, Mössbauer and magnetic parameters presented considerable alterations in comparison with those for bulk materials, as a consequence of mechanosynthesis. The modification of BiFeO 3 with 5 mol% of Mn ions do not induces significant microstructural or structural alterations in as-milled or annealed samples. However, an intense magnetization decreasing was observed. [ABSTRACT FROM AUTHOR]

In this work, pure and La 3+ -doped PBN56 ceramics (La 3+ added from 0 wt% to 4 wt%) were fabricated and studied concerning its structure, microstructure and dielectric properties. The analysis of the microstructure of the ceramics showed a change of the grain morphology for ceramics with La content higher than 1.0 wt%. X-ray diffraction and Raman spectroscopy were performed to study the structure of the PBN56 ceramics. The results showed the presence of an orthorhombic phase, whose concentration is increased with the increasing of the La 3+ content. The analysis of the results was performed to investigate the presence of the orthorhombic phase and the composition where its formation begins. [ABSTRACT FROM AUTHOR]

Leucine, α-methyl leucine and two peptides were exposed tospace conditions on board the MIR station during the Perseus-Exobiology mission. This long duration space mission was aimed at testing the delivery of prebiotic building blocks. Duringthis mission, two amino acids (leucine and α-methyl leucine) and two peptides (leucine-diketopiperazine and trileucine thioethylester) were exposed in Earth orbit for threemonths. Basalt, clay and meteorite powder were also mixed with the samples in order to simulate the effects of potential meteorite protection. Analysis of the material after the flight did not reveal any racemization or polymerisation but did provideinformation regarding photochemical pathways for the degradationof leucine and of the tripeptide. Amino acids appeared to be moresensitive to UV radiation than peptides, the cyclic dipeptide being found to be as particularly resistant. Meteorite powder which exhibits the highest absorption in Vacuum UltraViolet (VUV)afforded the best protection to the organic molecules whereasmontmorillonite clay, almost transparent in VUV, was the leastefficient. By varying the thickness of the meteorite, we found that the threshold for efficient protection against radiation was about 5 μm. The possible exogenous origin of biologicalbuilding blocks is discussed with respect to the stability to themolecules and the nature of the associated minerals. [ABSTRACT FROM AUTHOR]

All-trans-retinoic acid is a potent inhibitor of cell proliferation and inducer of differentiation. However, the clinical use of all-trans-retinoic acid in the treatment of cancer is significantly hampered by its toxicity and the prompt emergence of resistance, believed to be caused by increased all-trans-retinoic acid metabolism. Inhibitors of all-trans-retinoic acid metabolism may therefore prove valuable in the treatment of cancer. In this study, we characterize R116010 as a new anticancer drug that is a potent inhibitor of all-trans-retinoic acid metabolism. In vitro, R116010 potently inhibits all-trans-retinoic acid metabolism in intact T47D cells with an IC(50)-value of 8.7 nM. In addition, R116010 is a selective inhibitor as indicated by its inhibition profile for several other cytochrome P450-mediated reactions. In T47D cell proliferation assays, R116010 by itself has no effect on cell proliferation. However, in combination with all-trans-retinoic acid, R116010 enhances the all-trans-retinoic acid-mediated antiproliferative activity in a concentration-dependent manner. In vivo, the growth of murine oestrogen-independent TA3-Ha mammary tumours is significantly inhibited by R116010 at doses as low as 0.16 mg kg(-1). In conclusion, R116010 is a highly potent and selective inhibitor of all-trans-retinoic acid metabolism, which is able to enhance the biological activity of all-trans-retinoic acid, thereby exhibiting antitumour activity. R116010 represents a novel and promising anticancer drug with an unique mechanism of action. [ABSTRACT FROM AUTHOR]

Complex dielectric permittivity measurements in PbNb2O6 ceramics were performed in a frequency and temperature range of 1 kHz–1 MHz and from 15 to 900 K, respectively. The results revealed two dielectric anomalies showing typical characteristics of relaxor ferroelectric materials at cryogenic temperatures. Comparison with other tetragonal tungsten bronze (TTB) structure-type materials suggests the existence of successive phase transitions, which until now were not reported. The observed low temperature dielectric behaviors seem to be due to intrinsic physical characteristics related to the TTB structure. [ABSTRACT FROM AUTHOR]