Magnetoelectric and magnetodielectric effect in BST–LSMO ferromagnetic/ferroelectric composites

Ba_1?xSr_xTiO₃ (BST) for x = 0.20, 0.25 and 0.30 and La_0.67Sr_0.33MnO₃ (LSMO) are synthesized using hydroxide co-precipitation route to lead to nanocrystalline particles of BST and LSMO respectively. Further the magnetoelectric (ME) and magnetodielectric (MD) composites of BST0.20, BST0.25 and BST0.30 are formed by addition of the LSMO at y = 0.1 and y = 0.2. The parent BST compositions are studied for its dielectric properties as a function of temperature and frequency up to 1 MHz. The AC conductivity of LSMO–BST (LBST) is studied and it confirms the conduction to be due to small polarons. The paper also presents ME and MD properties of LBST composites. The observation on MD properties show that the dielectric constant possesses contribution due to magnetic field dependant interfacial polarization and variation due to the stress induced because of the applied magnetic field. Further from the ME study, the maximum value of magnetoelectric coefficient is 15.51 mV/Oe/cm is observed for LBST composites.     

Magnetoelectric coupling in ordered arrays of multilayered heteroepitaxial BaTiO₃/CoFe₂O₄ nanodots

Fully epitaxial BaTiO(3)/CoFe(2)O(4) ferroelectric/ferromagnetic multilayered nanodot arrays, a new type of magnetoelectric (ME) nanocomposite with both horizontal and vertical orderings, were fabricated via a stencil-derived direct epitaxy technique. By reducing the clamping effect, ferroelectric domain modification and distinct magnetization change proportional to different interfacial area around the BaTiO(3) phase transition temperatures were found, which may pave the way to quantitative introducing of ME coupling at nanoscale and build high density multistate memory devices.     

High-Q Magnetoelectric Nickel–Quartz–Nickel Structures

The results of experimental examination of the magnetoelectric parameters of three-layer nickel–quartz–nickel structures in the region of electromechanical resonance are presented. The structures have been fabricated by electrolytic deposition of nickel onto a quartz substrate. It has been found that their Q-factor in the region of electromechanical resonance is Q = 10000, which is considerably higher than the Q-factors of magnetoelectric structures fabricated earlier. The experimental data agree well with the earlier-presented theory.     

Characterization of novel borides in Ti–Nb–Zr–Ta + 2B metal-matrix composites

Metal-matrix composites consisting of a complex quaternary Ti-35Nb-7Zr-5Ta alloy reinforced by borides have been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, tantalum, and, titanium diboride (TiB₂) powders, using the laser engineered net-shaping (LENS?)¹ process. The microstructures of the as-deposited composites have been characterized using scanning electron microscopy, orientation microscopy, and, transmission electron microscopy. Both primary and eutectic boride precipitates, exhibiting the orthorhombic B27 structure, are observed in these as-deposited composites. The complex primary borides exhibit an unusual compositional variation within the same precipitate, which has been investigated in detail using site-specific characterization with a transmission electron microscope. The ability to form near-net shape components using the Laser Engineered Net Shaping process makes these laser-deposited composites promising candidates for wear-resistant applications in biomedical implants.     

Specific Features of the Magnetoelectric Effect in Permendur–Quartz–Permendur Structures in the Region of Electromechanical Resonance

Technical Physics Letters - The experimental frequency and field dependences of the magnetoelectric effect in three-layer permendur–quartz–permendur structures in the region of...     

A novel ultrasonic transducer backing from porous epoxy resin–titanium–silane coupling agent and plasticizer composites

In this paper, a new composite for ultrasonic attenuation backing has been successfully fabricated from porous epoxy resin containing titanium (Ti), silane coupling agent and plasticizer composites. The effect of Ti particles on the network structure and mechanical properties of epoxy resin has been analyzed in detail. The ultrasonic parameters in epoxy composites have been measured by a conventional pulse-echo-overlap technique at a frequency of 1–5 MHz. The effect of Ti content and temperature on the longitudinal sound velocity and attenuation of epoxy resin composites were investigated. Precise in situ observations of the acoustic properties such as attenuation and acoustic impedance of epoxy composites are expected to be useful for ultrasonic transducer systems for new as well as for backing application with high attenuation.     

Toughening characterization in alumina platelet–hydroxyapatite matrix composites

Fracture toughness of Al₂O₃ platelet-reinforced hydroxyapatite (HAP) ceramics was investigated using the Vickers' indentation technique. The geometrical anisotropy of alumina platelets induces an anisotropic toughening. The efficiency of reinforcing mechanisms remains maximum for a crack propagating with an angular deviation inferior to 30° around the direction perpendicular to alumina disc faces. This is assumed to result from a crack deflection mechanism which induces a favorable contribution of mode II failure. A small effect of hydroxyapatite grain size becomes noticeable in the direction parallel to alumina disc faces. The toughening depends on the size and volume content of alumina platelets. Large size platelets provoke a spontaneous microcracking of the HAP matrix which is detrimental to the mechanical reliability, whereas small platelets lead to a strong toughening. The results relate to the intensity of thermoelastic residual stresses within the matrix around alumina inclusions. © 1999 Kluwer Academic Publishers     

Investigation of TaC–TaB<Subscript>2</Subscript> ceramic composites

The TaC–TaB₂ composition was sintered by spark plasma (SPS) at 1900–2100°C and applied pressure of 30 MPa. TaC and 2–3 wt% B₄C were used as starting powders. Densification process, phase evolution, microstructure and the mechanical properties of the composites were investigated. The results indicated that the TaC–TaB₂ composition could be SPS to 97% of theoretical density in 10 min at 2100°C. Addition of B₄C leads to an increase in the density sample from 76 to 97%. B₄C nano-powder resists grain growth even at high temperature 2100°C. The formation of TaB₂/carbon at TaC grain boundaries helps in pinning the grain boundary and inhibiting grain growth. The phase formation was associated with carbon and boron diffusion from the starting particles B₄C to form TaB₂ phases. TaC grain sizes decreased with increase in B₄C concentration. Samples with 2.0 wt% B₄C composition had highest flexure strength up to 520 MPa. The effect of B₄C addition on hardness measured by microhardness has been studied. Hardness of samples containing 3.0 wt% B₄C was 16.99 GPa.     

Effect of amphiphilic coupling agent on heat flow and dielectric properties of flax–polypropylene composites

The study on heat transport in composites is of fundamental importance in engineering design and for tailoring thermal and mechanical behaviour of materials. In this study, the thermal conductivity and thermal diffusivity of flax reinforced polypropylene (PP) composites were determined at room temperature. Chemical modification in the form of a biodegradable zein coating was applied to the flax nonwovens. The effect of fibre loading and chemical modification on the thermo-physical properties was investigated. Dielectric permittivity studies were also evaluated and the dielectric constant of fibre reinforced composites was found to be higher than that of PP. The heat flow and crystallinity effects of the composites were also determined by differential scanning calorimetric (DSC) studies. Zein modification of the flax fibres resulted in a decrease of thermal conductivity and diffusivity which was attributed to a decrease in velocity and mean free path of phonons due to increase in interfacial adhesion.     

Growth of eutectic composites in the InSb–MnSb system

Eutectic composites in the InSb–MnSb system have been grown by the Bridgman method in vertical geometry using a growth charge of eutectic composition. The composites consisted of a [110]-oriented single-crystal InSb matrix and single-crystal MnSb needles aligned in the growth direction. As the solidification rate was raised from 0.5 to 6 mm/h, the length of the needles increased, whereas their diameter dropped from 20 to 4 µm. Further raising the solidification rate led to spontaneous crystallization. Characteristically, the electrical and magnetic properties of the eutectic composites in the InSb–MnSb system were found to exhibit large anisotropy. The low-temperature resistivity of the composites across the needles is four to five times that along the needles. With increasing temperature, the resistivity ratio drops by up to a factor of 2–3. This can be accounted for in terms of a geometric factor. The electrical conductivity of the composites is determined primarily by the MnSb phase, whose volume along the growth direction was considerably larger. According to magnetic measurements, the eutectic composites in the InSb–MnSb system are ferromagnets with a Curie temperature of ? 600 K.     

Optimization of delamination factor in drilling GFR–polypropylene composites

Glass fiber-reinforced polypropylene composites often replace the conventional materials due to their special or unique mechanical properties. As the applications of these composites increase for a number of industries, drilling of these composites is inevitable for subsequent composite product manufacturing stage. In the drilling of composites, the thrust force is induced during the drilling operation; as a result, it causes damage. This damage is characterized by the delamination factor, which depends on the machining parameters such as speed of the spindle, feed rate, and drill diameter. The study on the delamination in the drilling of glass fiber-reinforced polypropylene is limited and has been carried out comprehensively. The effect of machining parameters on delamination in the drilling of glass fiber-strengthened polypropylene (GFR-PP) composites is studied through the Box–Bhenken design. Response surface method, along with the desirability analysis, is used for modeling and optimization of delamination factor in the drilling. The result proves that the models are effectively used to forecast the delamination in the drilling of GFR-PP composites. Also, the result indicates that the foremost issue that influences the delamination is the feed rate.     

Interfacial reactions in aluminum alloys/mullite–zirconia composites

Mullite and reaction-sintered mullite–zirconia bars were exposed to Mg- and Mg+Cu-containing molten aluminum alloyS, at 800°C for up to 2000 h, and afterwards characterized by X-ray diffraction (XRD), reflected light optical microscopy (RLOM) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). Mullite was completely attacked by Al penetrating through grain boundaries and reducing the mullite grains to alumina and silicon. Mullite–zirconia was not attacked, because the dense net of ZrO₂-grains prevented penetration of molten metal into the compact and, consequently, a mechanically and thermodynamically stable spinel layer (≈30 μm) was formed at the static interface, which protected the ceramic against further attack.     

In situ enhancement of toughness of SiC—TiB2 composites

A process based on liquid phase sintering and subsequent annealing for grain growth is presented to obtain the in situ enhancement of toughness of SiC–30 wt%, 50 wt%, and 70 wt% TiB2 composites. Its microstructures consist of uniformly distributed elongated -SiC grains, relatively equiaxed TiB2 grains, and yttrium aluminium garnet (YAG) as a grain boundary phase. The composites were fabricated from -SiC and TiB2 powders with the liquid forming additives of Al2O3 and Y2O3 by hot-pressing at 1850°C and subsequent annealing at 1950°C. The annealing led to the in situ growth of elongated -SiC grains, due to the phase transformation of SiC, and the coarsening of TiB2 grains. The fracture toughness of the SiC–50 wt% TiB2 composites after 6 h annealing was 7.3 MPa m1/2, approximately 60% higher than that of as-hot-pressed composites (4.5 MPa m1/2). Bridging and crack deflection by the elongated -SiC grains and coarse TiB2 grains appear to account for the increased toughness of the composites.     

One-step synthesis of mesoporous silica–graphene composites by simultaneous hydrothermal coupling and reduction of graphene oxide

Silica–graphene oxide composites were synthesized by hydrothermal method with simultaneous functionalization and reduction of graphene oxide (GO) in the presence of mesoporous silica. Two types of silica were used in the study, mesoporous synthetic silica (MSU-F) synthesized by sol-gel method and mesoporous mineral silica (meso-celite) from pseudomorphic synthesis. The infrared spectra of the composites showed the disappearance of the carboxyl peak at 1735 cm^-1 which could be due to the reduction of the –COOH group. The enhancement of the band at 1385 cm^–1 is attributed to the vibration of the Si–O–C=O moiety formed by reaction of the –COOH group of GO and the silanol (Si–OH) of silica. The Raman spectra of the composites show a diminished intensity ratio of D to G band indicating that GO was reduced to graphene sheets. The TEM images demonstrate the coupling of silica to GO surface revealing dense loading of silica on GO in planar structure.