Phase formation and electrical properties of BNLT–BZT lead-free piezoelectric ceramic system

Phase formation study in lead-free piezoelectric ceramics based on lanthanum doped bismuth sodium titanate (Bi_0.4871Na_0.4871La_0.0172TiO₃:BNLT) and zirconium doped barium titanate (BaZr_0.05Ti_0.95O₃:BZT), has been carried out in the system of (1−x)BNLT–xBZT where x = 0.0–1.0, by two-step mixed oxide method. It was observed that the addition of BZT in the BNLT ceramics developed the dielectric and piezoelectric properties of the ceramics with the optimum piezoelectric constant (d₃₃) and dielectric constant (ε_r) at room temperature of about 138 pC/N and 1651, respectively, from the 0.2 BNLT to 0.8 BZT ceramic sample. The Curie temperature (T_C) of this ceramic was found at 295 °C which is 195 °C higher than that of pure BZT ceramics, promising the use of this ceramic in a higher range of temperature.     

Synthesis and magnetic properties of Co–Zn magnetic fluid

Co_1−xZn_xFe₂O₄ (with x varying from 0 to 0.7) nanoparticles to be used for ferrofluid preparation were prepared by chemical co-precipitation method. The fine particles were suitably dispersed in transformer oil using oleic acid as the surfactant. The magnetization (M_s) and the size of the particles were measured at room temperature. The magnetization (M_s) was found to decrease with the increase in zinc substitution. The magnetic particle size (D_m) of the fluid was found to vary from 11.19 to 4.25 nm decreasing with the increase in zinc substitution.     

Study of cohesive,electronic and magnetic properties of the Ni–In intermetallic system

Cohesive, electronic and magnetic properties of the intermetallic system Ni–In, specifically the stable phases Ni₃In-hP8, Ni₂In-hP6, NiIn-hP6 and Ni₂In₃-hP5, have been investigated. At present, these materials are of great interest in connection to the application of the In–Sn alloys as lead-free micro-soldering alloys, and considering Ni as the contact material. In spite of this, scarce literature regarding basic thermodynamic properties of the Ni–In intermetallic phases has been found. Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations is used. All the calculations include spin polarization. Structural parameters, formation energies and cohesive properties of the different phases are studied through minimization of internal parameters. The electronic density of states (DOS) is analyzed for each optimized structure. We found that the NiIn-hP6 phase is the most stable one and only the Ni₃In-hP8 phase exhibits magnetic properties.     

Structural and magnetic properties of nanostructured Mn–Al–C magnetic materials

Pre-alloyed Mn_50+x−yAl_50−xC_y   (x=0$x=0$, 2, 4, 6, 8; y=0$y=0$, 1.7, 3) powders were mechanically milled (MM), and the as-milled powders subsequently annealed at temperatures from 350 to 600 °C to produce the ferromagnetic metastable L1₀-structured τ-phase. Bulk Mn₅₄Al₄₆ specimens were also annealed under the same conditions for comparison. The effects of the Mn concentration and C additions on phase formation, microstructure, magnetic properties, as well as on the magnetization mechanism of the Mn–Al–C alloys were systematically investigated. It was found that the magnetic properties are strongly dependent both on the fraction of the τ-phase and its microstructure. There exists a strong influence of the microstructural refinement, due to the ball milling, on the rate of ε-phase to τ-phase transformation and on the stability of the τ-phase. The kinetics of formation and subsequent decomposition of the magnetic τ-phase were markedly different in the MM and bulk alloys. Both remanence curves and δM plots showed no exchange coupling among the τ-phase nanograins. The mechanism for the magnetization process was determined to be domain wall pinning.     

Dielectric loss,conductivity relaxation process and magnetic properties of Mg substituted Ni–Cu ferrites

The dielectric properties, dc and ac electrical resistivities of Mg substituted Ni–Cu ferrites with general formula Ni_0.5Cu_0.5−xMg_xFe₂O₄ (0.0≤x≤0.5) have been investigated as a function of frequency, temperature and composition. ac resistivity of all the samples decreases with increase in the frequency exhibiting normal ferrimagnetic behavior. The frequency dependence of dielectric loss tangent showed a maximum in between 10 Hz and 1 kHz in all the ferrites. The conductivity relaxation of the charge carriers was examined using the electrical modulus formulism, and the results indicate the presence of the non-Debye type of relaxation in the prepared ferrites. Similar values of activation energies for dc conduction and for conductivity relaxation reveal that the mechanism of electrical conduction and dielectric polarization is the same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the distribution of relaxation time is temperature independent. The saturation magnetization and coercivity as calculated from the hysteresis loop measurement show striking dependence on composition.     

Propagation of SH waves in layered functionally gradient piezoelectric–piezomagnetic structures

Abstract

The propagation of SH waves is studied in two bonded semi-infinite material, one piezoelectric and the other piezomagnetic. Both materials are functionally gradient materials. The material properties of the two materials vary in two directions, one parallel to the interface and the other perpendicular to the interface. The dispersion relations are obtained in explicit forms for different forms of the non-homogeneities. The effects of gradient variation about material constants on the frequency of SH waves and on the wave numbers are shown graphically.     

Structural and magnetic properties of Fe–Ni mecanosynthesized alloys

Fe_100???x Ni _x samples with x?=?22.5, 30.0 and 40.0 at.% Ni were prepared by mechanical alloying (MA) with milling times of 10, 24, 48 and 72 h, a ball mass to powder mass (BM/PM) ratio of 20:1 and rotation velocity of 280 rev/min. Then the samples were sintered at 1,000°C and characterized by X-ray diffraction (XRD) and transmission Mössbauer spectrometry (TMS). From the refinement of the X ray patterns we found in this composition range two crystalline phases, one body centered cubic (BCC), one face centered cubic (FCC) and some samples show FeO and Fe₃O₄ phases. The obtained grain size of the samples shows their nanostructured character. Mössbauer spectra were fitted using a model with two hyperfine magnetic field distributions (HMFDs), and a narrow singlet. One hyperfine field distribution corresponds to the ferromagnetic BCC grains, the other to the ferromagnetic FCC grains (Taenite), and the narrow singlet to the paramagnetic FCC grains (antitaenite). Some samples shows a paramagnetic doublet which corresponds to FeO and two sextets corresponding to the ferrimagnetic Fe₃O₄ phase. In this fit model we used a texture correction in order to take into account the interaction between the particles with flake shape and the Mössbauer $\upgamma$ -rays.     

Preparation and magnetic properties of Fe–Ag granular alloy

An aqueous solution of AgNO₃ in the presence of ammonia and Fe(CO)₅ is sonicated under a H₂/Ar mixture, yielding a nanostructured homogeneous phase of Ag/Fe₂O₃. This composite material is further reduced at 300°C under hydrogen to produce the nanophased Fe/Ag solid mixture. The as-prepared material, as well as the reduced mixture, is analyzed by various conventional methods. Magnetization loops, ESR, Mössbauer, and magnetoresistance measurements are also conducted to determine the magnetic properties of the products.     

Transient absorption–dispersion properties of four-level atomic system via elliptically polarized probe light and magnetic field

A novel four-level atomic system which interacted by an elliptically polarized probe field and a control laser field in the presence of external magnetic field is proposed. Here, we are interested in the transient properties of a weak probe field due to its potential application on quantum computing and quantum communication. It is shown that the external magnetic field and relative phase between two electric field components of the probe field can influence the probe absorption and dispersion.     

Structural and magnetic properties of HCP-CoCrPt–SiO2 granular media

Granular HCP-(CoCrPt)_100−x(SiO₂)_x thin films with Cr underlayers have been fabricated by sputtering multilayers followed by post-deposition annealing. Magnetic and structural properties of the films for potential applications in magnetic recording media have been investigated in detail. In as-deposited films coercivities exceeding 2.5 kOe have been obtained with SiO₂ varying from 8 to 16 vol%; high coercivity of 5.6 kOe and anisotropy of 4.6×10⁶ erg/cm³ have been achieved at low M_rt value (about 0.4 memu/cm²) in the post-annealed films. VSM measurements showed that the magnetic moment lies well in the film plane under proper preparation conditions. Grain isolation in the magnetic layer was improved by segregating SiO₂ into grain boundaries and further enhanced by post-deposition annealing. The rapid increase of the coercivity upon annealing is most likely due to the significant decrease in intergranular exchange coupling, as shown by the δM measurement in which the peak value of δM curves changed from a positive value to a negative value upon annealing. Magnetic reversal properties of the films have also been systematically studied. These results show that the HCP-CoCrPt–SiO₂ granular film is a promising candidate for ultra-high-density recording media up to 100 Gbit/in² or beyond because of its low Pt content and desirable properties.     

Structure and magnetic properties of co-sputtered Co–C thin films

We studied the structure and magnetic properties of co-sputtered Co_1−xC_x thin films using a transmission electron microscope (TEM) and a SQUID magnetometer. These properties were found to depend critically on deposition temperature, T_S, and composition, x. Generally, phase separation into metallic Co and graphite-like carbon phases proceeds with increasing T_S and decreasing x. Plan view and cross-sectional TEM images of the films prepared showed that Co grains about 10–20 nm in diameter and 30–50 nm in height are three-dimensionally separated by graphite-like carbon layers 1–2 nm thick. Optimum magnetic properties with saturation magnetization of 380 emu/cc and coercivity of 400 Oe were obtained for a film with x=0.5 and T_S=350°C.     

Studies of AC electrical conductivity and initial magnetic permeability of rare-earth-substituted Li–Co ferrites

In the present work, the AC electrical conductivity and initial magnetic permeability were investigated for some Rare-earth-substituted spinel ferrites. These ferrites are of composition Li_0.5−0.5xCo_xFe_2.4−0.5xR_0.1O₄ (where x=0.0$x=0.0$, 0.5, and 1; R=Y, Yb, Eu, Ho and Gd). They were prepared by standard ceramic techniques. With respect to AC electrical conductivity, measurements show dispersion with frequency at low temperatures. This dispersion obeys the universal power law. The frequency exponent of the power law decreases with both Co ion content and temperature. This indicates that the classical barrier hopping mechanism is the predominant one in these samples. On the other hand, the behavior of the initial magnetic permeability with temperature exhibits multidomain structure only for the samples with x=0.0$x=0.0$, and single domain structure otherwise.     

In situ fabrication and thermoelectric properties of PbTe–polyaniline composite nanostructures

PbTe–polyaniline (PANi) composite nanopowders were in situ fabricated via an interfacial polymerization method at room temperature (~293 K). The phase structure, composition, and morphology of the powders were characterized by X-ray powder diffraction, infrared spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM, respectively. The results show that the composite nanopowders consist of PbTe nanoparticles, PANi/PbTe core–shell nanostructure, and PbTe/PANi/PbTe three-layer sphere-like nanostructures. Formation mechanism of the PbTe–PANi composite nanostructures was proposed. The thermoelectric properties of the composite powders after being cold pressed into pellets were measured from 293 to 373 K. As the temperature increases from 293 to 373 K, the Seebeck coefficient of the composite decreases from 626 to 578 μV K⁻¹ and the electrical conductivity increases from 1.9 to 2.2 S m⁻¹.     

Microstructural and magnetic properties of Pr–BiCo co-substituted M-type Sr–Ca hexaferrites

We have synthesized the Pr–BiCo substituted hexaferrites with compositions of Sr_0.8-xCa_0.2Pr_xFe_12.0-x(Bi_0.5Co_0.5)_xO₁₉ (0.0?≤?x?≤?0.5) by the standard ceramic method. Results of X-ray diffraction analysis exhibits that the synthesized hexaferrites with x from 0.0 to 0.3 are in single magetoplumbite structure, and impurity phases are observed when x?≥?0.4. The surface morphology of magnets shows that hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The remanence first increases with x from 0.0 to 0.1, and then decreases when x?≥?0.1. The intrinsic coercivity decreases with x from 0.0 to 0.1, and then increases when x?≥?0.1. With x from 0.0 to 0.4, the changing trend of magnetic induction coercivity is in agreement with that of H_cj, while at x?≥?0.4, H_cb decreases. The maximum energy product initially increases with x from 0.0 to 0.2, and then decreases when x?≥?0.2.     

Microstructures and soft magnetic properties of as-deposited Fe–Sm–O thin films

The influences of O₂ partial pressure on saturation magnetization, coercivity and effective permeability of the as-deposited Fe–Sm–O thin films, which were fabricated by RF magnetron reactive sputtering method, were investigated. The nanocrystalline Fe_83.4Sm_3.4O_13.2 thin film fabricated at O₂ partial pressure of 5% exhibited the best magnetic softness with a saturation magnetization of 1.43 MA/m, coercivity of 65.2 A/m and effective permeability of about 2600 in the frequency range from 0.5 to 100 MHz. The electrical resistivity of Fe_83.4Sm_3.4O_13.2 was 130 μΩ cm. The microstructures and electrical resistivity were investigated in this work.     

Structural,electrical and magnetic properties of Zr–Mg cobalt ferrite

Spinel cobalt ferrite, CoFe_2−xM_xO₄ has been synthesized by substitution of the combination of metallic elements M=Zr–Mg by the microemulsion method using polyethylene glycol as a surfactant. Powder X-ray diffraction analysis reveals that the substitution results in shrinkage of the unit cell of cobalt ferrite due to higher binding energy of the synthesized samples. The energy-dispersive X-ray fluorescence analysis confirms the stoichiometric ratios of the elements present. The thermogravimetric analysis shows that the minimum temperature required for the synthesis of these substituted compounds is 700 °C. A two-point probe method was employed for the measurement of the electrical resistivity in a temperature range of 293±5 to 673±5 K. It appears that there is a decrease in the number of Fe²⁺/Fe³⁺ pairs at the octahedral sites due to the substitution and corresponding migration of some of the Fe³⁺ ions to tetrahedral sites, consequently increasing the resistivity and the activation energy of hopping of electron at the octahedral sites. The susceptibility data also suggest migration of Fe³⁺ to tetrahedral site in the initial stage, which results in an increase in A–B interactions leading to large increase in the blocking temperature (T_B) as observed in samples having dopant content x=0.1.     

Improvement of microstructure and magnetic properties of Nd–Fe–B alloys by Nb and Co additions

In order to establish the role of niobium on the hydrogenation, disproportionation, desorption and recombination (HDDR) behavior of near-stoichiometric alloys, two alloys: NdI3Fe8OB7 and Nd13Fe78Nb1Co1B7 (at%) were investigated before, during and after the HDDR process. The microstructure of the as-cast Nb-free alloy before employing the HDDR process was found to consist of three phases, the matrix Nd₂Fe₁₄B (φ) phase, Nd-rich phase and a significant amount of free iron; whereas, the microstructure of the Nb-containing alloy consisted of only the first two phases.     

Enhancement of ionic conductivity in the composite solid electrolyte system: TlI–Al2O3

This paper reports the heterogeneously doped alumina (Al₂O₃) on the ionic conductivity of thallium iodide. Composite materials of formula (1 − x) TlI–xAl₂O₃, x = 0–0.7 have been prepared and studied by X-ray diffraction, differential scanning calorimetry, and electrical conductivity. X-ray diffraction and differential scanning calorimetry proved the formation of composite in this binary system. The maximum enhancement observed is about three orders of magnitude with respect to the host material. The enhancement of electrical conductivity in comparison with pure thallium iodide can be interpreted with the space charge layer model. Moreover, the increased content of alumina in the system leads to the disappearance of phase transition β–α thallium iodide, which is usually observed in the pure compound. This behavior was explained by stabilizing effect of β-phase at high temperatures and suppression of α-phase at higher contents of alumina.     

Pressure effects on magnetic properties and martensitic transformation of Ni–Mn–Sn magnetic shape memory alloys

The mechanism for the effects of pressure on the magnetic properties and the martensitic transformation of Ni-Mn- Sn shape memory alloys is revealed by first-principles calculations. It is found that the total energy difference between paramagnetic and ferromagnetic austenite states plays an important role in the magnetic transition of Ni-Mn-Sn under pressure. The pressure increases the relative stability of the martensite with respect to the anstenite, leading to an increase of the martensitic transformation temperature. Moreover, the effects of pressure on the magnetic properties and the martensitic transformation are discussed based on the electronic structure.