bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Chromate-Intercalated Layered Double Hydroxides
Authors: del Arco Margarita , Carriazo Daniel , Martín Cristina , Pérez Grueso Amalia M. , Rives Vicente
Published: March 2009

PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N2 adsorption at -
196 °C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been
used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion
exchange method from the corresponding chloride LDH (layered double hydroxides) precursors.
The results indicates that the oxometalate intercalation in both systems produces interlayer
microporosity and a basal spacing of 8.7 Å; This gallery height decreases when the samples are
calcined in the temperature range 100-300 °C, due to a grafting process. A larger thermal stability is
detected for MgAl-CrO4 sample than for the zinc-containing one.
Development of GF/PP Towpreg Woven Fabrics for Composite Reinforcements
Authors: Sousa Fangueiro Raul Manuel Esteves , Nunes João Pedro , Silva João F. , de Araújo Mário , Novais Fernando
Published: March 2009

In the present work, glass fibre polypropylene (GF/PP) woven fabrics were manufactured from cost-effective flexible thermoplastic towpregs produced by a developed dry coating process. The paper describes the modifications made on the developed coating line to allow producing thermoplastic towpregs able to be woven in textile equipments. The produced fabrics were observed under optical microscopy and submitted to tests in order to evaluate their textile-like properties, glass fibre content and flexibility. Composites processed from those fabrics by compression moulding were also submitted to mechanical testing in order to assess their performance. The obtained experimental results have shown that the woven fabrics produced are cost-effective and present properties good enough to be applied in large-scale commercial markets (e.g. automotive). Future research efforts will be carried to try decreasing the towpreg frictional properties and the amount of polymer lost during the textile processing and improving the feeding technology to warp yarns directly from a creel.
Nanostructure Evolution during Uni-Axial Deformation of PET – A WAXS and SAXS Study Using Synchrotron Radiation
Authors: Viana Julio , Mano João F. , Denchev Zlatan Z. , Oliveira Maria Jovita , Cramez Maria Clara
Published: March 2009

In this work, the structural evolution and damage of PET during stretching is assessed by
wide- and small-angle X-ray scattering (respectively, WAXS and SAXS) experiments in specimens
pre-deformed at different strain levels (ex-situ characterization). Injection moulded PET rectangular
tensile specimens were stretched (at 2 mm/min) into the plastic domain in a universal test machine
at different strain levels at room temperature. The structure of the central zone of the deformed
specimens was then characterized by WAXS and SAXS experiments using an X-ray synchrotron
source. PET was initially (before stretching) amorphous. A strong molecular orientation in the
stretching direction is quickly developed for the initial plastic deformation levels, evidenced by
strong equatorial WAXS reflections. This orientation rapidly levels off, remaining constant during
further stretching. The WAXS patterns are accompanied with no reflections on SAXS, evidencing a
local ordering phenomenon, typical of nematic liquid-crystalline structures. The SAXS patterns
evidence the occurrence of some voiding in the cold drawing regime just after yielding. These
anisotropic voids are oriented perpendicular to the stretching direction, as in a craze-like structure.
The void size drastically increases at the onset of the strong strain hardening behaviour.
Using Atomic Force Microscopy to Retrieve Nanomechanical Surface Properties of Materials
Authors: Graça Sergio , Colaço Rogerio , Vilar Rui
Published: March 2009

When atomic force microscopy is used to retrieve nanomechanical surface properties of
materials, unsuspected measurement and instrumentation errors may occur. In this work, some error
sources are investigated and operating and correction procedures are proposed in order to maximize
the accuracy of the measurements. Experiments were performed on sapphire, Ni, Co and Ni-30%Co
samples. A triangular pyramidal diamond tip was used to perform indentation and scratch tests, as
well as for surface visualization. It was found that nonlinearities of the z-piezo scanner, in particular
the creep of the z-piezo, and errors in the determination of the real dimensions of tested areas, are
critical parameters to be considered. However, it was observed that there is a critical load
application rate, above which the influence of the creep of the z-piezo can be neglected. Also, it was
observed that deconvolution of the tip geometry from the image of the tested area is essential to
obtain accurate values of the dimensions of indentations and scratches. The application of these
procedures enables minimizing the errors in nanomechanical property measurements using atomic
force microscopy techniques.
Combination of IBA Techniques for Composition Analysis of GaInAsSb Films
Authors: Corregidor Victoria , Chaves P.C. , Reis M.A. , Izarra Carlos Pascual , Alves Eduardo , Barradas Nuno P.
Published: March 2009

Quaternary GaInAsSb films alloys were grown by MOVPE technique on GaSb
substrates with different growth conditions such as substrate orientation and thickness. The
composition of the films determines their bandgap, and also how well they are lattice matched
to the substrate. It is thus essential to determine it accurately, which is not a trivial task in this
system. The composition of the samples was studied with a combination of Particle Induced Xray
Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) experiments. The
RBS experiments were done with a 2 MeV 4He+ or H+ ion beam, according to the thickness of
the films, and were used to determine the thickness of the samples. The PIXE experiments were
performed at grazing angle conditions and provided accurate elemental composition
information. It was found that for thin layers (300 nm) there is a dependence of In incorporation
into the matrix according to the substrate orientation, although this tendency was not found for
thicker films (24m).
Characterisation of Roman Mortars from the Archaeological Site of Tróia (Portugal)
Authors: Silva António Santos , Paiva M. , Ricardo J. , Salta Manuela M. , Monteiro A.M. , Candeias António Estevao
Published: March 2009

Roman mortars from the industrial archaeological site of Tróia (Portugal) have been
studied by means of chemical, mineralogical and microstructural analysis. The mortars are calcitic
aerial lime mortars differing in the type and proportion of aggregates used, including crushed
carbonaceous rocks (limestone and dolomite), siliceous sand and crushed ceramics. The results
show that although these mortars have been subjected to a very aggressive environment they are
still in a very good state of conservation.
Leaching Process of Cerium Extraction from Mixture of Cerite-Monazite Mineral
Authors: Gomes José Cosme Cunha , Souza C.P. , Gomes Uilame Umbelino , Gavarri Jean R. , Dallas Jean P. , Leroux C.
Published: March 2009

Rare earth oxides have been widely investigated in catalysis as structured and electronic
promoters to improve the activity and thermal stability of catalysts. Cerium has an important role in
three-way catalysis and fluid catalytic cracking, two significant catalytic processes by their
economic relevance and tonnage. Cerium and other rare earths have been studied as possible
heterogeneous catalysts at selective oxidation of hydrocarbons. Cerite and monazite are minerals
with high concentration of cerium element. Extraction of cerium metal using conventional leaching
processes has shown low yields or high costs. The main purpose of this research work is to optimize
the parameters in cerium purification stage from this mineral using leaching process. To separate
particles with different granulometries, the mineral is ground and fractioned with sieves of 80, 200,
250 and 400 mesh. In order to put off organic components and oxidize cerium(III) to cerium(IV),
samples were roasted at 1073K by twenty-four hours. The roasted samples were solubilized by acid
attack (leaching) for approximately twenty-four hours; according to the acid used hydrochloric or
sulfuric), cerium and other trivalent elements are solubilized as chloride or sulfate solution. Cerium
was extracted by selective precipitation at pH~3,4 using ammonium or natrium hydroxide as pH
changer. After filtration and drying, the precipitated product was characterized by XRD (x-ray
diffraction), and then process efficiency was determined (cerium percentage and the different
phases in the powder). Particles granulometry, roasting process (time and temperature), as well as
leaching parameters (acid used, time, temperature and concentration of reagents) were the main
variables studied.
New Ceramic Products from Slate and Aluminium Sludge Wastes
Authors: Martins Isabel M. , Xavier Claudino , Mendonça Maria Helena , Oliveira Manuela
Published: March 2009

Previous studies had shown that a promising material could be obtained by mixing
aluminium-rich sludge with slate powder (with Al2O3:SiO2 molar proportion of 2:1), shaping by
uniaxial pressing and sintering at 1300oC, in order both to detoxify the sludge by fixing the metals
in a leach-resistant ceramic matrix and to yield a new material from the reactions of the above
compounds at high temperature. In view of potential applications, since this material was also found
to be inert after leaching tests, a further systematic study, reported in the present paper, was carried
out, in order to determine its mechanical properties and discuss them in function of the
microstructure. The average values of Vickers hardness HV3 (683), bend strength (126 MPa),
Young's modulus (161GPa) and fracture toughness (3.35 MPa.m1/2) are significantly higher than
those found for the as sintered slate powders, which is attributed to the increased fraction of α-
alumina and reduced content of glassy phase in the microstructure of the material with sludge
addition.
Texture – Property Relationships in Bi-Layered Ferroelectric Ceramics: A Case Study of SrBi2Ta2O9
Authors: Amorín Harvey , Kholkin Andréi L. , Costa Maria Elisabete V.
Published: March 2009

A quantitative model for the calculation of spontaneous polarization of BLSF ceramics as a function of the degree of texture is presented using a general formalism based on the texture analysis via an orientation distribution function. The March-Dollase equation was selected to fit the measured texture distribution because its fitting parameters can be related to experimentally measurable stereological values obtained from SEM images. The results are applied to the
SrBi2Ta2O9 (SBT) system, which is a well-known member of the BLSF family. The textured SBT ceramics were fabricated by templated grain growth (TGG) and the microstructure and degree of texture were evaluated by SEM analysis, which allowed correlating the texture development to the sintering parameters. Enhanced ferroelectric properties were measured perpendicularly to the
uniaxial pressing direction of the ceramics, revealing the influence of the grains orientation, anisotropy and volume fraction of textured material on the ferroelectric properties. Finally, the predicted values for the spontaneous polarization as a function of the degree of texture were compared with those measured from the hysteresis loops.
Incorporation of Aluminium Residues in Dense Cordierite Formulations
Authors: Oliveira Fernando A. Costa , Delmas Francisco , Araújo Ana , Fernandes Jorge Cruz , Dias Diamantino
Published: March 2009

Additions of γ-Al2O3 and Al(OH)3 powders produced at INETI from spent baths resulting
from the aluminium transformation industry were made to a commercial cordierite batch
formulation (without Al2O3 addition), known as DC4, developed by Rauschert Portuguesa Lda., in
order to evaluate the possibility of replacing with benefits the conventional α-Al2O3 source used.
The resulting samples were found to be denser than the commercial ones. This is related to the
higher reactivity of these particular sources of alumina as compared to that added to the commercial
product. Consequently, higher Young’s modulus (100-114 GPa) and flexural strength (80-98 MPa)
were achieved for the developed materials in comparison to those obtained for commercial
cordierite (96±2 GPa and 67±5 MPa, respectively). In addition, slightly lower thermal expansion
coefficients were observed (3.6x10-6 K-1) and the thermal shock resistance was found to increase
from 325 K to 350 K.
The developed technology can be regarded as suitable for reducing the environmental impact of
deposition of wastes from the aluminium transformation industry.
Prediction of Solid Waste Incineration Residues Quantity for Valorization in Lightweight Aggregates
Authors: Quina Margarida J. , Almeida Marisa A. , Santos Regina C. , Bordado João C. , Quinta-Ferreira Rosa M.
Published: March 2009

The recycling of wastes is nowadays a priority in terms of the EU policies. This study
aims at the replacement of a certain percentage of clay (natural raw material) by residues produced
in a municipal solid waste incineration (MSWI) process referred as Air Pollution Control (APC)
residues. The main objective of this work concerns the prediction of the quantity of the waste that
can be valorized as lightweight aggregates (LWA). For this analysis the Riley diagram was
considered, which consists in plotting the percentage concentration of the main oxides (SiO2, Al2O3,
fluxing) in a ternary diagram. The fluxing is defined as the sum of Fe2O3+CaO+MgO+Na2O+K2O.
Our results point out that no more than 5% of APC residues should be considered, since the main
oxide composition of APC residues is far away from bloating area. A pre-washing treatment
improved the waste characteristics being then possible to increase the amount of residue that can be
incorporated in percentages below 10%. This theoretical analysis can save experimental work, since
it allows the prediction of the maximum amount of wastes to be tested.
Regeneration of Adsorbent Carbonaceous Materials with Supercritical Water
Authors: Sánchez-Montero M.Jesus , Salvador-Palacios Francisco , Palacios Aurelio Salvador , Rodriguez M.Jesus Martin
Published: March 2009

The aim of this work was to study a new procedure for the regeneration of activated carbon
saturated with phenol. The study was accomplished in two steps: extraction of the pollutant with
supercritical water at 410 °C and 275 bar, and gasification of phenol with supercritical water at
temperatures ranging between 600 - 650 °C. It was observed that the regeneration process was very
rapid and effective. The regenerated activated carbon always recovered its original adsorption
capacity, even after several regeneration cycles. The gasification of phenol afforded CO2 and H2O,
with a very fast first-order kinetic process. The activation energy was very low (0.192 kJ mol-1).
Effect of Lead Content and B-Site Substitutions on Dielectric and Piezoelectric Properties of PZT Ceramics
Authors: Dimitriu Elena , Craciun Floriana , Cernea Marin , Ramer Rodica
Published: March 2009

The behaviour of the dielectric and piezoelectric properties of doped PZT ceramics, with variable lead content, has been investigated from –50oC to room temperature. The PZT materials were prepared by the oxide technique and samples were sintered as pellets, at various temperatures. Niobium and lithium ions have been substituted for Ti4+, Zr4+ in the PZT matrix, and a small amount of Bi2O3 was added to cause A-position vacancies. The lead content in the four materials
prepared varies in a narrow range, from 0.97 to 1.029 lead atoms, while the concentration of all other components are maintained constant. The microstructure of samples, evaluated by SEM technique and XRD analysis evidenced the presence of the tetragonal phase characteristic for the
PZT 52/48. The dielectric and piezoelectric c onstants measured on poled samples depends on the sintering temperature, defects and domain walls, lead content.
Optical Properties of PLZT 9/65/35 Thin Films on ITO-Coated Glass Substrate
Authors: Khodorov Anatoli , Gomes M.J.M.
Published: March 2009

Lanthanum modified lead zirconate titanate (PLZT) thin films were fabricated on indium doped tin oxide (ITO) - coated glass substrate by sol-gel method. The structure of the films was characterized with XRD and SEM. In the case of PLZT the dielectric function was modelled as a sum of Lorentzian oscillators and found by fitting the transmittance and reflectance spectra measured at normal incidence in the wavelength range of 220-2400 nm. The anomalous behaviour of dielectric
function was observed below the absorption edge that was suggested to be due to formation of some defect states. The evolution of the absorption edge as well as dielectric function with film thickness was observed and discussed.
Ferroelectric and Dielectric Characteristics of Bi3.25La0.75Ti3O12 Thin Films Prepared by the Polymeric Precursor Method
Authors: Simões A.Z. , Ramírez M.A. , Stojanović B.D. , Marinković Z. , Longo Elson , Varela José Arana
Published: March 2009

The ferroelectric properties and leakage current mechanisms of preferred oriented
Bi3.25La0.75Ti3O12 (BLT) thin films deposited on La0.5Sr0.5CoO3 (LSCO) by the polymeric precursor method were investigated. Atomic force microscopy indicates that the deposited films exhibit a dense microstructure with a rather smooth surface morphology. The improved ferroelectric and leakage current characteristics can be ascribed to the plate-like grains of the BLT films.
Anomalous Broad Dielectric Dispersion of 0.4PZN-0.3PSN-0.3PZN Relaxor Ceramics at Lower Temperatures
Authors: Banys Juras , Macutkevic Jan , Brilingas Algirdas , Samulionis Vytautas , Bormanis K. , Sternberg Andris , Zauls Vismantas
Published: March 2009

Dielectric properties of 0.4PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3-0.3PbMg1/3Nb2/3O3- (0.4PZN- 0.3PSN-0.3PMN) ceramics are presented for 200 < T < 500 K and 20 Hz < ν < 1 MHz. Dielectric constant is very high (more 14000) in the vicinity of the peak. Anomalous broad dielectric relaxation have been observed near the temperature of the maximum permittivity, Tm (at 1 kHz).
External bias field considerably lowers the value of dielectric losses at low frequencies due to decrease of polar nano regions contribution to the dielectric permittivity.
Microstructure and Thermal Features of a-Si:H and nc-Si:H Thin Films Produced by Rf Sputtering
Authors: Thaiyalnayaki V. , Cerqueira M.Fátima , Macedo Francisco , Ferreira João Alves
Published: March 2009

Amorphous and nanocrystalline silicon thin films have been produced by reactive r.f.
sputtering and their microstructure, optical and thermal properties were evaluated. A good correlation was found between the microstructure determined by Raman spectroscopy and X- ray diffraction and the thermal transport parameters.
The Characterization of Two Dimensional Electrostrictive CuInP2S6 Materials for Transducers
Authors: Samulionis Vytautas , Banys Juras , Vysochanskii Yulian
Published: March 2009

The electromechanical properties of layered, two-dimensional materials of CuInP2S6
family have been investigated. It was shown that, at room temperature, which is above phase transition and under DC bias electric field, these materials behave as a piezoelectric because of electrostriction. In this case, the piezoelectric and electromechanical coupling coefficients are odd functions of the bias field and have a linear dependence on the bias field. The relative changes of ultrasonic velocity are found to have a quadratic dependence on the bias DC field. In bias fields of
about 20 kV/m, the values of square of electromechanical coupling coefficient could be high enough (>20%) for longitudinal vibrations in thin plates of investigated CuInP2(S,Se)6 materials in the paraelectric phase. In the ferroelectric phase, the external DC electric field acts as polarizing field and electromechanical coupling coefficients sufficiently increase. At the transitions, the piezoelectric anomalies have been observed.
Processing and Characterization of (1-x)(Na1/2Bi1/2)TiO3 - xLa(Mg1/2Ti1/2)O3 Ceramics
Authors: Salak Andrei N. , Vyshatko Nikolai P. , Kholkin Andréi L. , Ferreira Victor M. , Olekhnovich Nikolay M. , Radyush Yury V. , Pushkarev Anatol V.
Published: March 2009

Lead-free relaxor ceramics based on sodium-bismuth titanate, (1-x)(Na1/2Bi1/2)TiO3 - xLa(Mg1/2Ti1/2)O3 [(1-x)NBT-xLMT] (0≤x≤0.25), were prepared by both the conventional mixed oxide method and by the Pechini route, and their crystal structure and dielectric properties were investigated. All the compositions studied were found to possess a rhombohedrally distorted crystal
lattice at room temperature. A distortion degree of the unit cell decreases and its volume increases with LMT content. The temperature of the dielectric permittivity maximum does not change with increasing substitution rate. As x is increased, the frequency-dependent dielectric peaks are flattened. The compositional evolution of structure and dielectric characteristics of the ceramics obtained are analysed and discussed in respect to size, charge and polarizability of the cations involved.
Effect of NaNbO3 Crystalline Aggregates on the Electrical Properties of SiO2-Na2O-Nb2O5 Glass-Ceramics
Authors: Graça Manuel P.F. , Ferreira da Silva Maria Gracinda , Valente Manuel A.
Published: March 2009

The presence of NaNbO3 crystallites in a glass matrix has scientific and technological interest due to their electrical properties and potential applications in microwave, pyroelectric and piezoelectric devices. A glass with the composition 60SiO2-30Na2O-10Nb2O5 (% mole) was prepared by the melt-quenching method. NaNbO3 microcrystallites were precipitated on the surface of the glass by
heat-treatment. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, dc and ac conductivity measurements were used in the study of the glass and glassceramic materials. The number of particles, precipitated in the surface of the glass-ceramic samples, increases from the 650 to the 750°C and decrease in the 800°C sample. In all these samples the particles size thickness increases with the rise of the heat-treatment temperature. In the 750 and
800°C samples it was observed the presence of a white surface layer formed by NaNbO3 crystallites aggregations. The dc conductivity (σdc) decreases with the rise of the heat –treatment temperature up to 750°C and the dielectric constant value, at 1kHz and room temperature, has a maximum value of 34.94 for the 800 °C treated sample.
Ferromagnetism and Ferromagnetic Resonance in Mn Implanted Si and GaAs
Authors: Sobolev Nikolai A. , Oliveira Marcio A. , Amaral Vitor S. , Neves Armando , Carmo M. Celeste , Wesch Werner , Picht Oliver , Wendler Elke , Kaiser Ute , Heinrich J.
Published: March 2009

Ferromagnetism persisting above 375 K and anisotropic ferromagnetic resonance (FMR) spectra have been detected for the first time in Si co-implanted with Mn and As and annealed under appropriate conditions. For comparison, semi-insulating GaAs samples have been implanted with the same ions and subsequently annealed. They also exhibit ferromagnetism with a Curie temperature well in excess of 375 K. High-resolution transmission electron microscopy (TEM) performed on the samples with the best magnetic characteristics has shown the presence of
nanoclusters due to the segregation of the implanted species in both Si and GaAs. The angular dependence of the FMR spectra also reveals the existence of magnetic clusters with the hard magnetization axis aligned along the four equivalent <111> crystal axes. The spectra are very similar in Si and GaAs, indicating that the clusters in both materials probably consist of hexagonal MnAs.
The Effects of Ca and Mn Excess Co-Doping in CMR Manganites Solid Solution Structures
Authors: Figueiras Fábio , Vieira Joaquim M. , Guzik M.E. , Legendziewicz J. , Tavares Pedro B. , Amaral Vitor S.
Published: March 2009

A comprehensive study of CMR manganite related phases, particularly those that develop under the effects of Ca and Mn-excess co-doping is undertaken. The relationships between phase composition, processing and observed crystalline structure are investigated for co-precipitated powders of composition La1-xCaxMn1+zO3+δ, thermally treated at 800 and 1000 °C in air for Ca
contents of x=0.10 and x=0.15 and Mn content from z=0 up to z=0.88.
A relevant structural transition from orthorhombic to rhombohedric symmetry is observed as a function of Mn excess near 25% A site vacancies. This solid solution is in equilibrium with the conjugated phases, either LaMn7O12 at 800°C, or Mn3O4 at 1000°C, respectively. Results suggest that at the polymorphic phase transition the solid solution is stable enough to slow down Mn diffusion into the perovskite cell. Ca-doping introduces stability in the perovskite structure and broadens the domain for phase formation reaction. The solid solution limit of the Ca-manganite solid solution is set above 50% Mn excess.
Spin Reorientation Transition and Exotic Magnetism in Dilute Gd1-xYx Single Crystals (x < 0.1) Revealed by A.C. Magnetoresistance Studies
Authors: Santos João A.M. , Sousa João Bessa , Araújo João P. , Correia F. , Collingwood J.F. , Palmer S.B.
Published: March 2009

We measured dilute Gd1-xYx single crystals (x < 0.1) samples using an a.c. magnetoresistance technique. This technique consists in applying a constant current to the sample and measuring the temperature dependent a.c. voltage under a time modulated external magnetic field (f = 333 Hz). The a.c. voltage signal is decomposed in real and imaginary components or, alternatively, in amplitude and phase signals relative to the a.c. magnetic field. This technique proved to be extremely sensitive and effective to display all the magnetic phase transitions revealed by the previous d.c. transport measurements, plus an additional spectrum of other critical features.
X-Ray Diffraction Study of Ordered Antiferromagnets for Tunnel Junctions
Authors: Franco Nuno , Alves Eduardo , Rickart M. , Guedes Anibal , Freitas Paulo , Barradas Nuno P.
Published: March 2009

Antiferromagnets (AF) such as MnPt and MnNi can be used in spin valves and tunnel junctions due to their high exchange coupling, high blocking temperature, and fair corrosion resistance. They are used as pinning layer in a AF/FM/barrier/FM structure, where FM is a ferromagnet such as CoFe and the barrier is an ultra-thin insulating layer. However, as deposited MnPt and MnNi films with thickness around 20 nm are in the fcc phase, and show no exchange bias in AF/FM bilayers. A transition from fcc to fct is required, and takes place upon annealing. We present an X-ray diffraction study of the phase transition in glass/Ta 7nm/Ru 3 nm/MnPt 20
nm/CoFe 5 nm/Ta 3 nm AF/FM bilayers. We observe the MnPt phase transition from fcc to fct around 250°C. We correlate the phase transition with the change of the bilayers magnetic properties.
Synthesis of BiFeO3 Ceramic Targets and Thin Film Deposition by Laser Ablation
Authors: Mardare Cezarina C. , Tavares Pedro B. , Mardare Andréi I. , Savu Raluca
Published: March 2009

A dense ceramic target of BiFeO3 was synthesized by the urea combustion method. X-ray diffraction indicates that this target is composed of a mixture of phases, the main one is BiFeO3, but Bi46Fe2O72 and Bi2Fe4O9 are also present in small amounts. The BiFeO3 target was used for depositing thin films on Pt/Ti/SiO2/Si substrates by the laser ablation technique. The depositions were made in oxygen atmosphere at pressures in the range between 5x10-3 and 2x10-2mbar, using a
KrF laser. The substrate temperatures were 450 or 500°C and the laser energy, the frequency and the distance between the target and the substrate were kept constant at 125mJ, 10Hz and 4cm, respectively. After a deposition time of 30minutes the thickness of the films was approximately 400nm. Some of the films were heat-treated in situ, in 100mbar O2 for 30minutes, at the same temperatures used for deposition. X-ray diffraction results show the BiFeO3 phase, as well as some
Bi46Fe2O72 and Bi2Fe4O9. The films were crystallized without any preferential orientation, but the ones made at 2x10-2mbar and 450°C were partially amorphous. For measuring the ferroelectric hysteresis loops, either Al top electrodes were deposited by thermal evaporation or Pt, by sputtering. The distorted shapes of the hysteresis loops obtained indicated that the films exhibit weak ferroelectric properties and high leakage current values.
Organic Materials for Active Layers in Transistors: Study of the Electrical Stability Properties
Authors: Gomes Henrique Leonel , Stallinga Peter , de Leeuw D.M.
Published: March 2009

Field effect transistors based on several conjugated organic materials were fabricated and assesed in terms of electrical stability. The device characteristics were studied using steady state measurements as well as techniques for addressing trap states. Temperature-dependent measurements show clear evidence for an electrical instability occurring above 200 K that is caused
by an electronic trapping process. It is suggested that the trapping sites are created by a change in the organic conjugated chain, a process similar to a phase transition.
Preparation and Properties of New Superconductor Material MgB2
Authors: Marinha D. , Oliveira Filipe J. , Reis Mário S. , Costa Florinda M. , Carrasco Maria Fátima , Araújo João P. , Sousa João Bessa , Vieira Joaquim M. , Amaral Vitor S.
Published: March 2009

Bulk MgB2 samples were synthesized by hot isostatic pressing under pressures up to 200MPa at 950°C. In these conditions, full densification of samples was obtained (~98% of theoretical density). SEM, EDS and XRD analysis on final dense bodies were used to evaluate samples, and show increasingly better control over the amounts of secondary MgO (down to ~10%) and complete prevention of formation of MgB4 by using simple glass encapsulation techniques and
addition of Mg(s) to the capsule. The samples display superconducting properties, including a narrow critical transition in electrical properties (Tc ~36-38K). Magnetic studies were performed, allowing the determination of the superconducting fraction and critical current density Jc of the
materials. Contrary to the Tc, the Jc is quite sensitive to the processing and microstructure and values from 0.3 to 0.6x106 A/cm2 are obtained at 10K. The reduction of Jc with the applied magnetic field requires further improvements to reduce weak links.
The Effect of Annealing Temperature on the Transport Properties of BSCCO Fibres Grown by LFZ and EALFZ
Authors: Carrasco Maria Fátima , Monteiro Jorge , Amaral Vitor S. , Silva Rui F. , Vieira Joaquim M. , Costa Florinda M.
Published: March 2009

Superconducting fibres of Bi-Sr-Ca-Cu-O system were grown by the conventional Laser Floating Zone (LFZ) process and by the new technique of Electrical Assisted Laser Floating Zone (EALFZ). The presence of an electric field during solidification process significantly changes the fibre microstructure with Bi2Sr2Ca2Cu3O10 nominal composition. The higher cristallinity of the asgrown
EALFZ fibres, resulting from the current application during solidification, leads to a
transformation rate enhancement during subsequent annealing. A strong correlation between the transport properties and the final microstructure of the annealed fibres is observed. The highest critical current density of the EALFZ fibres is obtained after heat treatment at 845°C while for the LFZ ones similar values are obtained only after annealing at 860°C.
Chromatic Dispersion in Ge-Doped SiO2-Based Single Mode Fibres due to Temperature Dependence of the Ultraviolet Absorption: Numerical and Experimental Results
Authors: André P.S. , Pinto Armando , Pinto J.L. , Ferreira Rute A. Sá , Nobre Sonia S. , Monteiro P. , Carlos Luís D.
Published: March 2009

The main information transmission limitation in optical communications employing SiO2
optical fibres is imposed by the optical pulses temporal broadening, resulting from the dispersive properties of the transmission medium (chromatic dispersion). Usually, this dispersion is modelled assuming a -0.4 meV/°C dependence of the 11 eV gap energy. We have monitored the 4.3 eV absorption band, with temperature and obtained a thermal dependence of -0.026 meV/°C. With this value we can predict the first and second order chromatic dispersion for a wavelength of 1550 nm.
Defect Formation in La2Ni(M)O4+δ (M= Co, Cu): Modelling and Coulometric Titration Study
Authors: Naumovich E.N. , Patrakeev Mikhail V. , Kharton Vladislav V. , Yaremchenko Alrksey A. , Tsipis Ekaterina V. , Logvinovich Dmitri I. , Frade Jorge R. , Marques Fernando M.B.
Published: March 2009

The p(O2)-T- diagrams of La2Ni1-xMxO4+ (M=Co and Cu, x= 0-0.20), determined by the coulometric titration technique at 923-1223 K in the oxygen partial pressure range 10-4 to 0.6 atm, can be adequately described by equilibrium processes of oxygen intercalation into the rock-salt type layers and hole localization on B-site cations forming 3+ oxidation states. For the hole activity, a non-ideal solution model taking into account the repulsion of p-type electronic charge carriers can be used. The electrostatic repulsion excludes occupation of nearest neighboring sites and leads to splitting of the energy levels for more distant sites. The affinity of Ni and Cu cations with respect to the hole localization is similar and cannot be statistically separated analyzing the oxygen nonstoichiometry data only. On the contrary, cobalt cations tend to remain in the trivalent state and Co3+ should be treated as a separate type of charged point defect. Oxygen vacancies formed in the perovskite-like layers due to intrinsic Frenkel disorder have no essential effect on the oxygen thermodynamics. As expected, the thermodynamic functions governing the intercalation-related processes are independent of defect concentrations.
Oxygen Permeability of Mixed Conducting Perovskite Lanthanum Gallate-Based Ceramics
Authors: Politova Ekaterina D. , Aleksandrovskii Vladimir V. , Zaitsev Sergey V. , Kaleva G.M. , Mosunov Alexander V. , Stefanovich Sergei Yu. , Avetisov A.K. , Suvorkin S.V. , Kosarev G.V. , Sukhareva I.P. , Sung Jae Suk , Choo K.Y. , Kim T.H.
Published: March 2009

The structure, microstructure, electric transport and oxygen permeation properties of
(La,Sr)(Ga,Mg,Fe)O3-δ ceramics with perovskite or brownmillerite structures have been studied. Oxygen permeability values of ~0.1 cm3/cm2·min has been revealed at 1000 K for the ceramics studied. The correlation of electroconducting properties of the LaGaO3-based ceramics with perovskite and brownmillerite structures to their oxygen permeability characteristics has been proved.
Microstructure and Electrical Conductivity of Yb2+xTi2-xO7-x/2 Materials
Authors: Levchenko Alexey V. , Abrantes João Carlos de Castro , Shlyakhtina Anna V. , Shcherbakova Lidia G. , Horovistiz Ana Lucia , Frade Jorge R.
Published: March 2009

The dependence of electrical conductivity of pyrochlore type Yb2+xTi2-xO7-x/2 materials shows that these materials are predominantly ionic conductors and are potential solid electrolytes for high temperature electrochemical applications. However, a detailed impedance study as a function of temperature revealed that a proper assessment of these materials must take into account significant effects of microstructure, composition and thermal history. At intermediate temperatures,
the impedance spectra can be described by a series association of well separated contributions, and these could be ascribed to the properties of grain interiors, internal interfaces, and external electrode/material interfaces. The bulk and grain boundary properties were thus assessed and related to changes in microstructure and composition. The firing conditions also exert significant effects on the transport properties, especially for compositions which might deviate from the expected single phase range.
New Oxide-Ion Conductors Ln2+xTi2-xO7-x/2 (Ln = Dy – Lu; x=0.096)
Authors: Shlyakhtina Anna V. , Abrantes João Carlos de Castro , Levchenko Alexey V. , Stefanovich Sergei Yu. , Knot'ko Alexandr V. , Larina Liudmila.L. , Shcherbakova Lidia G.
Published: March 2009

New oxide-ion conductors Ln2+xTi2-xO7-x/2 (Ln = Dy-Lu, x = 0.096; 35.5 mol. % Ln2O3· 64.5 mol.% TiO2)-LANTIOX with a disordered pyrochlore structure are obtained by coprecipitation with next thermal annealing at 1600°C. Their ionic conductivity in air at 740°C attains 5·10-3 S/cm for Ln2.096Ti1.904O6.952 (Ln= Lu, Yb), 10-3 S/cm for Ln2,096Ti1,904O6,952 (Ln=Tm, Er, Ho) and 10-
4S/cm for Dy2,096Ti1,904O6,952 due to the presence of defects in both the cation and anion sublattices. The materials contain ~4.8-10.6% LnTi anti-site defects. Ln2.096Ti1.904O6.952 ceramics are shown to be stable in the temperature range of 1400 to 1700°C. 1400°C-samples Ln2+xTi2-xO7-x/2 have lower ionic conductivity then 1600°C and 1690°C samples.
Structural and Magnetic Properties of New Zr(Fe0.8Cu0.2)2 and Zr(Fe0.8Cu0.1Co0.1)2 Hydrogen Storage Materials
Authors: Makridis Sofoklis S. , Konstantakou Mary , Steriotis Th.A. , Pavlidou Eleni , Efthimiadis K.G. , Daniil M. , Ioannidou A. , Kikkinidis E.S. , Stubos Athanasios K.
Published: March 2009

In this work we investigate the effect of hydrogen absorption/desorption at room
temperature on the structural, magnetic and microstructural characteristics of Zr(Fe0.8Cu0.2)2 and Zr(Fe0.8Co0.1Cu0.1)2. Hydrating kinetics of the as cast bulk samples have been examined while in both samples an anomalous behavior at the absorption part of the P-C curve has been observed. Co doped sample absorbs higher hydrogen content at lower pressure. Crystal structure analysis has
been performed by using the Rietveld method. Co free sample has saturation magnetization of 50.85 Am2/kg while Co doped sample has 54.04 Am2/kg at external field of 1.8 T. After hydrogenation the magnetization decreases. Thermomagnetic analysis in the range of 4.2 to 1100 K reveals that the Curie temperature of AB2 phases is in the range of 510 to 550 K. Scanning electron microscopy
with energy dispersive x-ray spectroscopy was used in order to examine the composition and surface morphology of the bulk samples. The grain size reduces due to hydrogenation and this is attributed to the more hysteretic magnetization curve.
Quality Control of Fuel Cells Channels
Authors: Silva Catarina , Coelho João M.P. , Abreu Manuel A. , Cabrita Freitas J. , Rodrigues Campos
Published: March 2009

The methods of dimensional control for solid surfaces are usually contact methods.
However, in fragile and reduced hardness surfaces, these methods present critical disadvantages. The method presented in this work aims to offer resources for the optimization of graphite components machined with laser through the measurement of the channels’ depth and shape. In this scope, the laser triangulation technique demonstrated to be a very useful tool in the quality control of graphite diffusers plates for fuel cell prototyping and in their future production.
Phase Separation on GaInAsSb Films for Thermophotovoltaic Devices
Authors: Corregidor Victoria , Franco Nuno , Alves Eduardo , Barradas Nuno P.
Published: March 2009

Ga0.81In0.19As0.14Sb0.86 layers were grown on (100)-Te doped GaSb substrates 2º missoriented towards (110), (111)A and (111)B directions by metalorganic vapour deposition (MOVPE) at 540 °C. X-ray reciprocal space maps done in symmetric (224) and asymmetric (115) directions show a super-lattice structure due to the phase separation with a 5 nm period and independent of substrate orientation. The x-ray maps show different stage of relaxation of the films
and in same cases an interdiffusion region near the substrate. Despite of the phase separation, channelling experiments with H ions as projectiles showed a good quality of the films. Channelling experiments show that the crystalline quality gets worse with increasing the In and As concentration.
Electrocatalytic Properties of La2Mg17 Based Metal Hydride Electrodes
Authors: Chen Yun , Sequeira César A.C.
Published: March 2009

With the goal to find hydride electrodes, the phase structure and electrochemical
characteristics of the as-cast and ball-milled La2Mg17 alloy with Ni additions were investigated. The addition of Ni was found to be an important factor for the earlier transformation to an amorphous alloy. When the addition of Ni reached 100 wt%, the ball-milled La2Mg17 alloy transformed into a homogeneous phase with high discharge capacity of 1060 mAh/g(La2Mg17) [530 mAh/g(La2Mg17+100 wt% Ni)]. The exchange current density and the kinetics of the amorphous
alloy were also found experimentally noticeably higher than those of corresponding crystal alloy.
Electrochemical Production and Characterization of Ni-Mo, Ni-Mo-P and Ni+Mo Coatings
Authors: Niedbała Jolanta
Published: March 2009

The electrochemical layers with molybdenum were obtained by electrodeposition from
citrate bath. The process was carried out under galvanostatic conditions. Structural investigations were conducted by X-ray diffraction method. It was ascertained that electrodeposited Ni-Mo-P alloys are characterized by amorphous structure, Ni-Mo alloys are characterized by nanocrystalline structure whereas Ni+Mo composite layers have a crystalline structure. The chemical composition was determined using X-ray fluorescence spectroscopy method. It was stated that Ni-Mo-P alloys
contain 75%Ni, 10%Mo and 15%P, the Ni-Mo alloys contain 90%Ni and 10%Mo, Ni+Mo composite layers contain 90%Ni and 10%Mo. These layers were characterized by electrochemical methods (j=f(E) voltammetry and corrosion resistance by Stern method). The results of corrosion tests show that from among obtained layers the highest corrosion resistances exhibit nanocrystalline
Ni-10%Mo alloys.
Effect of the HAZ Microstructural Gradient on the Unstable Fracture Behaviour of Welds in a High Strength Steel
Authors: Teixeira Pedro , Loureiro Altino , Rodrigues Dulce Maria Esteves , Neves José
Published: March 2009

This paper presents the results of an investigation aimed at correlating the gradient of microstructures with the mechanisms of fracture and with J-toughness in the heat-affected zone (HAZ) of submerged arc welds on a high strength structural steel. The microstructure of the weld metal is composed of refined acicular ferrite while the microstructure of the coarse grained heataffected zone (CGHAZ) is basically formed by coarse bainite with a small proportion of martensite and primary ferrite in the grain boundary of the large prior austenite grains. A significant decrease
in toughness is observed with an increasing incursion of the fatigue crack front into the CGHAZ. The degradation in toughness is definitely brought about by the CGHAZs of the welds, the size and distribution of these zones being relevant factors in the weld performance.
Surface Integrity of H13 ESR Mould Steel Milled by Carbide and CBN Tools
Authors: Marques Maria José , Outeiro J.C. , Dias A. Morão , M'Saoubi Rachid , Chandrasekaran Hariharan
Published: March 2009

The quality of a mechanical component such as its geometrical accuracy stability and
fatigue life are significantly affected by the surface integrity generated by machining process. Residual stresses are a major part of the mechanical state of a machined layer and they can be beneficial or detrimental depending of their nature and magnitude. This study concerns phase analysis and residual stress profile characterization by X-ray diffraction (XRD) technique and microhardness profile of AISI H13 ESR mould steel, milled using carbide and CBN tools.
Analysis of the cross-section of the AISI H13 ESR samples, milled using both tools, reveal a martensitic microstructure, with a very thin layer heavily deformed due to the machining process. However, no phase transformation was detected by XRD.
Concerning the residual stresses, the results show that they are predominantly compressive at the samples surface. However, depending of the cutting tools, the in-depth residual stresses profiles present different evolutions. This difference in the in-depth residual stresses profiles between the two kind of cutting tools is attributed to the different cutting tool parameters, including the tool geometry.
Dislocation Microstructure in Copper Multicrystals Deformed under the Sequences: Rolling - Tension and Tension - Rolling
Authors: Sakharova Nataliya A. , Fernandes José Valdemar
Published: March 2009

The microstructure evolution of copper multicrystalline sheets, undergoing plastic
deformation in the sequences of strain paths rolling – tension and tension – rolling, was studied in the present work. For both sequences, two different types of change of strain path were studied: the tensile and rolling directions were parallel and normal to each other. Samples submitted to these four complex strain paths were investigated by transmission electron microscopy (TEM). TEM observations have shown the typical dislocations microstructures for the prestrain paths in tension
and rolling. The dislocation microstructures observed during the second path were analysed and discussed as a function of the sequence and of the type of strain path change (parallel and normal sequential paths). Special microbands features were observed during the second path, for both sequences, rolling – tension and tension – rolling. The appearance of such microstructural features is discussed in terms of the sequence and type of strain path change and it is linked with the slip
activity during the second deformation mode.
The Signal Characteristics of the Spectral Response of Bragg Grating Sensor Embedded in Composite Laminated after the Cure Process
Authors: Ramos Carlos A. , Frazão Orlando , Dias Ireneu , Marques António Torres
Published: March 2009

The objective of this work was to study, understand and evaluate the effect of different geometric configurations of carbon plies, in the reflected wavelength spectrum of Bragg grating structure together with the effect of the recoating process of the sensor. The different possibilities depend upon the orientation and location of the optical fibre relative to the composite reinforcement orientation and the presence/absence of recoating. The material stacking sequence and the cure
conditions were are also studied and the influence of the different possibilities was considered. The optical spectrum response obtained by the interaction of the optical fibre with the host material is shown.
Physical Cutting Model of Polyamide Composites (PA66 GF30)
Authors: Mata Francisco , Reis Pedro , Davim J. Paulo
Published: March 2009

Polymeric matrix composite materials presents advantages in a great number of
applications due to their high specific strength and stiffness, wear resistance, dimensional stability, low weight and directional properties. As result of these properties and potentials applications exists a strong need to understand the manufacturing processes, particularly the machining process of
these composite materials. This paper presents an investigation above the modelization of the cut, turning of small workpieces, on two materials: a polymer PA 6 (Polyamide) and a composite PA 66-GF30 (reinforced with 30% of glass fiber). The tests were carried out polycrystalline diamond tools (PCD). The objective of this experimental study is to evaluate the influence of the glass fiber reinforcement on the friction angle (ρ), shear angle (Φ), normal and shear stresses (σ, τ), chip deformation (ε) under the cutting parameters prefixed (cutting velocity and feed rate). The experimental model was compared with the theoretical model of Merchant.