Institute of Materials Physics and Engineering

Anversa degli Abruzzi, Italy

Institute of Materials Physics and Engineering

Anversa degli Abruzzi, Italy
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Koval V.,Slovak Academy of Sciences | Skorvanek I.,Slovak Academy of Sciences | Durisin J.,Slovak Academy of Sciences | Viola G.,Institute of Materials Physics and Engineering | And 5 more authors.
Journal of Materials Chemistry C | Year: 2017

Partial substitution of isovalent rare-earth ions for bismuth is one of the most effective ways to develop room temperature BiFeO3-based multiferroic materials with high resistivity and strong magnetoelectric coupling. However, their structures and properties are composition and processing sensitive, with the underlying mechanisms still far from being completely understood. Here we report on the structural, thermal and magnetic properties of polycrystalline Bi1−xTbxFeO3 (0 ≤ x ≤ 0.30) dense ceramics prepared by spark plasma sintering (SPS). The X-ray diffraction study reveals that increasing terbium content induces a structural transformation from the parental rhombohedral (R3c) polar phase to an orthorhombic (Pnma) non-polar phase at x ≈ 0.20-0.25. Complementary Raman and energy-loss near-edge structure (ELNES) spectroscopy studies indicate that the transition proceeds by the progressive loss of Bi-O hybridization. Suppression of the long-range ferroelectric ordering upon Tb substitution and loss of ferroelectricity at x ≥ 0.25 was also confirmed by differential scanning calorimetry. High-sensitivity magnetic measurements show that the introduction of a small amount of Tb3+ ions at the A-sites of the perovskite structure gives rise to the occurrence of spontaneous magnetization at room temperature. The reduced degree of Fe 3d-4p orbital mixing and the weaker Fe 3d-O 2p hybridization, revealed by ELNES and X-ray near-edge absorption fine structure (NEXAFS) analyses, suggest that the substitution-induced changes in the electronic structure are responsible for the enhanced magnetization in Tb-doped BiFeO3. Among the biphasic (R3c + Pnma) compositions with ferroelectric order, the Bi0.8Tb0.2FeO3 compound shows the highest value of remanent magnetization (Mr ≈ 0.26 emu g−1), which makes this material a potential candidate for magnetoelectric applications. © The Royal Society of Chemistry.

Viola G.,Institute of Materials Physics and Engineering | D'Isanto F.,Institute of Materials Physics and Engineering | Mahmoud A.E.R.,South Valley University | Reece M.J.,Queen Mary, University of London | And 3 more authors.
Ceramics International | Year: 2017

The present study illustrates the effects of processing conditions on phase and microstructure of CaGeO3 ceramics. It is shown that the fabrication of single phase, high density and crack-free CaGeO3 ceramics is particularly challenging using conventional sintering or spark plasma sintering. The main difficulties in achieving single phase are predominantly related to the segregation of an additional phase identified as Ca5Ge3O11, most likely driven by the volatilization of GeO2 during processing at high temperature. This can be mainly suppressed by adding an appropriate excess amount of GeO2. High density can be achieved by conventional sintering and spark plasma sintering (SPS), but in the temperature ranges that lead to the formation of Ca5Ge3O11. The presence of cracks observed in the ceramics is attributed to the development of local residual stresses caused by the anisotropy of the thermal expansion and elastic properties, and it can be avoided under certain SPS conditions. © 2017 Elsevier Ltd and Techna Group S.r.l.

Mahmoud A.E.-R.,South Valley University | Mahmoud A.E.-R.,Institute of Materials Physics and Engineering | Afify A.S.,Institute of Materials Physics and Engineering | Mohamed A.,Taibah University | Mohamed A.,The Higher Institute of Optics Technology HIOT
Journal of Materials Science: Materials in Electronics | Year: 2017

Lead-free (Ba1−xCax)(Ti0.9Sn0.1)O3 perovskite ceramics (x = 0.02–0.5) (BCTS) were synthesized using the solid-state reaction technique. X-ray diffraction was used to identify the formed phases of the prepared compositions. The morphology of ceramics has been studied using a scanning electron microscope equipped with an energy dispersive spectrometer. Field emission scanning electron microscope was used to examine the morphology of sensing film calcined powder. The crossover from BCTS single-phase (x = 0.02) to BCTS composite(x = 0.5) was obtained via coexistence of both (x = 0.3) of Ca addition. The composite powder was sintered at higher temperature rather than the single-phase powder. The calcined powder sensing film was prepared by the screen-printing technique as humidity sensors. Thereafter, DC resistance measurements were performed in the presence of relative humidity RH at room temperature. All the compositions exhibited a poor sensitivity toward the humidity sensing in the range of 0–98% RH. The compositions 0.02 and 0.06 have shown orthorhombic–tetragonal phase transition (TO−T) below the room temperature, while the other compositions have shown a pure tetragonal phase. The highest value of permittivity at Curie temperature (ε = 29241 at 100 Hz) and piezoelectric coefficient (d33 = 495 pC/N) at room temperature were obtained at Ca = 0.06 due to present polymorphic phase transition. The effect of frequency on the dielectric constant and dielectric loss at room temperature were investigated. All the prepared compositions exhibited small values of dielectric loss from 50 Hz up to 100 KHz, which indicates a good reliability for electronic applications such as capacitors or memory devices. © 2017 Springer Science+Business Media New York

Ferraris M.,Institute of Materials Physics and Engineering | Salvo M.,Institute of Materials Physics and Engineering | Casalegno V.,Institute of Materials Physics and Engineering | Ventrella A.,Institute of Materials Physics and Engineering
International Journal of Applied Ceramic Technology | Year: 2012

The results of an experimental investigation on epoxy-joined silicon carbide tested in shear mode by four different configurations of torsion test are presented and compared to results obtained by asymmetric four-point bending and four different lap tests in compression. All samples have been joined by an epoxy adhesive (Araldite AV119) which is to be considered as a model brittle joining material chosen to obtain several joined samples in a reasonable time. Advantages and disadvantages of each configuration are discussed and compared to results previously obtained with epoxy-joined Carbon/Carbon composites and ceramics tested with the same methods. © 2012 American Ceramic Society.

Ning H.,University of Mary | Mastrorillo G.D.,Institute of Materials Physics and Engineering | Grasso S.,University of Mary | Du B.,University of Mary | And 6 more authors.
Journal of Materials Chemistry A | Year: 2015

Magnesium tin silicide based thermoelectrics contain earth abundant and non-toxic elements, and have the potential to replace established commercial thermoelectrics for energy conversion applications. In this work, porosity was used as a means to improve their thermoelectric properties. Compared to dense samples of Sb doped Mg2Si0.5Sn0.5 with a maximum zT of 1.39 at 663 K, porous samples (37% porosity) prepared by a pressure-less spark plasma sintering technique showed significantly lower thermal conductivity and higher Seebeck coefficient, resulting in an increased maximum zT of 1.63 at 615 K. The possible origins of the enhanced Seebeck coefficient can be attributed to a change of carrier concentration and modification of the band structure, produced by microstructural engineering of the surface composition and particle-particle contacts. This journal is © The Royal Society of Chemistry.

Viola G.,Queen Mary, University of London | Viola G.,Institute of Materials Physics and Engineering | Tan Y.,Queen Mary, University of London | McKinnon R.A.,Queen Mary, University of London | And 3 more authors.
Applied Physics Letters | Year: 2014

The polarization response of 0.95[0.94(Bi0.5Na(0.45)Li0.05)TiO3-0.06BaTiO3]-0.05CaTiO3ceramics was studied under weak applied cyclic electric fields with different amplitudes and frequency. The analysis of the polarization signals showed that in the ferroelectric phase the non-linearity is dominated by a Rayleigh-type dynamics, while in the ergodic relaxor phase the polarization response deviates from the Rayleigh-type behaviour due to the occurrence of short range electric field-induced transitions, evidenced by the presence of four distinct frequency independent current broad peaks in the current-electric field loops, which gives rise to a characteristic non-linear polarization-electric field loop with reduced hysteresis and weak frequency dependence. © 2014 AIP Publishing LLC.

Rizzo S.,Institute of Materials Physics and Engineering | Grasso S.,Queen Mary, University of London | Salvo M.,Institute of Materials Physics and Engineering | Casalegno V.,Institute of Materials Physics and Engineering | And 2 more authors.
Journal of the European Ceramic Society | Year: 2014

CVD-SiC coated C/SiC composites (C/SiC) were joined by spark plasma sintering (SPS) by direct bonding with and without the aid of joining materials. A calcia-alumina based glass-ceramic (CA), a SiC+5wt%B4C mixture and pure Ti foils were used as joining materials in the non-direct bonding processes. Morphological and compositional analyses were performed on each joined sample. The shear strength of joined C/SiC was measured by a single lap test and found comparable to that of C/SiC. © 2013 Elsevier Ltd.

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