Structural, electrical and magnetic properties of Cu1−xZnxFe2O4 ferrites (0 ≤ x ≤ 1)

Copper–zinc ferrites bearing chemical formula Cu_1−xZn_xFe₂O₄ for x ranging from 0.0 to 1.0 with the step increment of 0.2 were prepared by the standard solid-state technique. The variation of Zn substitution has a significant effect on the structural, electrical and magnetic properties. Lattice parameters ‘a’ increased from 8.370 to 8.520 Å. Dielectric constant decreased up to 311 with the increase in frequency from 80 Hz to 1 MHz at room temperature. All the samples follow the Maxwell–Wagner's interfacial polarization. Saturation magnetization, magnetic moment and Yafet–Kittel angles were also determined. The possible reasons responsible for the change in density related, electrical and magnetic properties with the increase in Zn concentration are undertaken.     

Investigation of the local response of the steel–concrete interface for corrosion measurement

An equivalent circuit representation for the steel–concrete interface is determined from direct potential measurements at the steel surface. The local response of steel–concrete interface to a given polarization applied at the concrete surface is investigated using an Ag/AgCl embedded reference electrode and a test system which allows simultaneous measurements at the steel–concrete interface and on the concrete surface. It is shown that the impedance spectrum on Nyquist plot for the steel–concrete interface comprises of a single arc. The equivalent circuit representation of the steel–concrete interface comprising of a parallel combination of a constant phase element (CPE) and a resistance was found to be suitable for representing the observed frequency response above 10 mHz. The parameters for the equivalent circuit obtained from the frequency-domain impedance measurements are shown to provide close prediction of the transient time-domain response from a linear polarization resistance measurement. The equivalent circuit was found to be suitable for interpreting the transient response of the steel–concrete interface during the linear polarization measurements. Available results indicate that while the response of steel undergoing active corrosion exhibits a distinctive CPE behavior, the passive steel approaches a pure capacitor. The value of resistance when the measured current increases linearly with time during a linear polarization measurement from the concrete surface provide acceptable measurements of the charge transfer resistance, and the Ohmic resistance of the concrete.     

A far-field airborne radar NDT technique for detecting debonding in GFRP–retrofitted concrete structures

A far-field airborne radar (FAR) nondestructive testing (NDT) technique integrating inverse synthetic aperture radar (ISAR) measurements and a backprojection algorithm for the condition assessment of glass fiber reinforced polymer (GFRP)–wrapped concrete structures is proposed. The method is directed toward the detection of near-surface defects and delaminations located in the vicinity of GFRP–concrete interface. Normal and oblique incidence measurement schemes were adopted and studied for their effectiveness in detecting near-surface anomalies. This technique is also applied to the detection of rebars in reinforced concrete cylinders. Laboratory measurements in the frequency range 8–12 GHz were made on artificially damaged GFRP–concrete cylinders for validating the concept of this technique. Spatial resolutions (range and cross-range) are improved by integrating radar measurements at different azimuth angles and in different frequencies, and implementing the developed progressive image focusing scheme. The feasibility of the proposed FAR NDT technique for distant inspection is validated through these studies.     

Magnetic and electrical properties of NdNiSn

Magnetization and resistivity measurements have been carried out on the equiatomic ternary compound NdNiSn in the temperature range 2–200 K. The compound crystallizes in the orthorhombic CeNiSn-type structure with space group Pna2₁. Magnetic susceptibility shows a distinct feature at T_N=3 K (Néel temperature), typical of a phase transition from an antiferromagnetic to paramagnetic state. In the paramagnetic regime, the magnetic susceptibility obeys Curie–Weiss behavior yielding an effective magnetic moment μ_eff=3.32μ_B at lower temperatures, and 3.88 μ_B at higher temperatures. The reduction in the magnetic moment at lower temperatures is attributed to a crystalline electric field (CEF) effect, while the slight excess of magnetic moment at high temperatures compared to that of the free Nd³⁺ ion (3.62 μ_B) indicates that only a very small magnetic moment, at most 0.3 μ_B, is induced at the Ni sites. The electrical resistivity exhibits metallic behavior and no anomaly is observed at the respective Néel temperature. Analysis of the resistivity data in terms of crystalline electric fields including s–d electron scattering reveals that the ground magnetic state for the Nd³⁺ ions is a doublet of J=±5/2 states, with a first exited doublet of J=±7/2 states having an energy splitting of 56 K, with the next exited multiplet 139 K above the ground levels. These results are in fairly good agreement with those reported in the literature based on magnetic susceptibility and heat capacity measurements.     

Structural and magnetic susceptibility studies of samarium substituted magnesium–zinc ferrites

Polycrystalline soft ferrites Mg_1−x–Zn_x–Fe_2−y–Sm_y–O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0; y = 0.0, 0.05 and 0.1) were prepared by usual ceramic method. The samples were characterized by X-ray diffraction and IR techniques. Magnetic properties have been studied from magnetization and (a)–(c) susceptibility measurements. The XRD patterns of all the samples reveal the formation of single-phase cubic spinel. The IR spectra show two strong absorption bands in the frequency range 300–800 cm⁻¹. The magnetization measurements exhibit the Neel's collinear ferrimagnetic behavior for x ≤ 0.2 and suggest non-collinear Y–K (Yaffet–Kittel) type magnetic ordering for x ≥ 0.4. The samples with x ≥ 0.8 are paramagnetic at and above the room temperature. Variation of ac susceptibility with temperature exhibit the single domain structure (SD) with x = 0.0 and multi-domain (MD) structure with x ≥ 0.2 on substitution of Zn²⁺ content. On substitution of Sm³⁺ content, the samples exhibit SD for x = 0.0, MD for x = 0.2 and MD to SP transition for x ≥ 0.4.     

The corrosion behavior of Cu–Al and Cu–Al–Be shape-memory alloys in 0.5 M H2SO4 solution

The corrosion behavior of Cu–Al and Cu–Al–Be (0.55–1.0 wt%) shape-memory alloys in 0.5 M H₂SO₄ solution at 25 °C was studied by means of anodic polarization, cyclic voltammetry, and alternative current impedance measurements. The results of anodic polarization test show that anodic dissolution rates of alloys decreased slightly with increasing the concentrations of aluminum or beryllium. Severe intergranular corrosion of Cu–Al alloy was observed after alternative current impedance measurement performed at the anodic potential of 0.6 V. However, the addition of a small amount of beryllium was effective to prevent the intergranular corrosion. The effect of beryllium addition on the prevention of intergranular corrosion is possibly attributed to the diffusion of beryllium atoms into grain boundaries, which in turn deactivates the grain boundaries.     

Magnetic study of Ti-substituted NiFe2O4 ferrite

The Ni_1+xTi_xFe_2−2xO₄ (0 ≤ x ≤ 0.1) ferrite systems prepared by a semi-chemical route, have been studied by electron paramagnetic resonance (EPR) at X-band, Mössbauer spectroscopy and magnetization measurements at various temperatures. EPR spectra of these samples comprise generally a broad and asymmetric EPR signal. The variation of g_eff and peak-to-peak line width ΔH_pp, with Ti concentration and temperature are attributed to the variation of dipole–dipole interaction and the superexchange interaction. Mössbauer spectra comprise two sets of sextet attributed to Fe³⁺ at two distinct sites-A and -B. Ti⁴⁺ ions are concluded to occupy the octahedral B-sites. Magnetic moment is found to decrease with the increase of Ti⁴⁺ concentration. The effective magnetic field H_eff at the A-sites also follows a similar trend. The reason is attributed to the canted structure of spins in the Ti-doped samples. An anomalous behavior at x = 0.015 is observed in the properties studied here and some sort of phase change is believed to occur at 473 K in these ferrites.     

Microwave absorption properties of Mn- and Ti-doped strontium hexaferrite

M-type strontium hexaferrite SrFe₉Mn_1.5Ti_1.5O₁₉ was synthesized by solid-state method. X-ray diffraction (XRD), scanning electron microscopic (SEM), energy dispersive spectrometer (EDS) and susceptometer were used for characterization of obtained powders. The ferrite–polymer composites with different ferrite ratios of 50%, 60%, 70% and 80% in polyvinylchloride matrix were prepared. The microwave absorption properties of these composites were investigated in 12–20 GHz frequency range. The results showed that the particle size had a wide range of distribution and the magnetoplumbite structure was formed in the sample. The composite with 70% ferrite content has shown a maximum reflection loss of −26 dB at 18.84 GHz with the −15 dB bandwidth over the extended frequency range of 16.4–19.4 GHz for an absorber thickness of 1.8 mm. It was concluded that the prepared composites could be good candidates for electromagnetic compatibility and other practical applications at high frequency.     

Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles

Microwave assisted combustion method was used to synthesize nanocrystalline Zn_xNi_1−xFe₂O₄ from a stoichiometric mixture of corresponding metal nitrates and urea powders. The structural, chemical and magnetic properties of Ni–Zn ferrite was determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM) and DC conductivity measurements. Results showed that the material was spinel structure with a high purity with an estimated crystallite size of 20 nm by X-ray line profile fitting. TEM analysis showed necked near-spherical particles with an average size of 20 nm, reflecting highly crystalline nature of these nanoparticles. Magnetic properties showed anomalities as the Zn doping level increased. This has been explained and attributed to the relative positions of Ni, Zn, and Fe ions in the crystal lattice.     

Determination of the elastic properties of some coated materials by simulation of the analogue signal of the reflection acoustic microscope

We discuss in this work the elastic properties of monolayer materials (layer/substrate). We consider both cases of quick/slow and slow/quick systems. We calculate Young's modulus, shear modulus and Poisson's ratio of the following four systems: Cr/Fe, TiN/Fe, Al/Si and Al/SiC. We make it evident that the use of the simulated acoustic signal of the reflection acoustic microscope yields to the determination of the wave propagation velocity of different modes in the layer/substrate according to the frequency and the thickness of the layer. We demonstrate that Victorov relation is not applicable in this case. A new method, that we called ‘method of homogenization’ is proposed to resolve the problem of dispersion.For the considered materials, the calculations have been carried out in a large range of frequencies (50 MHz–3.5 GHz) and coating layer thickness (0.5–150 μm). We show that for the studied materials the elastic constants take the values of the material layer beyond a thickness of 30–40 μm.     

Electrical behaviour of hydridofluorides of potassium–calcium KCaH3−xFx with x = 1, 1.5, 2, 2.5

This paper reports the results of the electrical conductivity measurements for KCaH_3−xF_x series with (x = 1, 1.5, 2, 2.5) in the temperature range 298–503 K.The activation energy of the electrical conductivity for the studied compounds depends on hydrogen amount and Reau's criteria. Differential thermal analysis curves were measured in the same temperature range 298–503 K.Possible correspondence between preferential order given by X-ray diffraction, thermal behaviour and electrical properties are discussed.     

Comparative studies of spectroscopic properties in Er–Yb codoped phosphate glasses

A spectroscopic investigation of an extensive series of commercially available Er³⁺–Yb³⁺ codoped phosphate glasses (IOG-1) with different Er–Yb concentrations have been presented based upon spectroscopic measurements and Judd–Ofelt theory. The composition and the atomic concentration of the respective elements of the glass samples were analyzed. Various spectroscopic parameters were obtained to evaluate the performances of these glasses as a laser material in the eye-safe laser wavelength of 1.53 μm. Using the measured fluorescence lifetimes the radiative quantum efficiency of the ⁴I_13/2 → ⁴I_15/2 transition is estimated to be 100% for the glass substrates with an Er³⁺ concentration of lower than 2.0 × 10²⁰ ions/cm³. The stimulated emission and absorption cross-sections were also determined and compared. The infrared and upconversion fluorescence were studied, and under 975 nm excitation the dominant upconversion mechanisms are excited state absorption (ESA) and energy transfer (ET) for the green emission, and ET for the red emission. The data obtained here provide useful guidelines on the choice of IOG-1 glasses with the fixed Er–Yb concentrations.     

Field trials for dynamic characteristics of railway track and its components using impact excitation technique

Assessment of condition of railway track is crucial for track design, repair, and effective maintenance operations. In-field dynamic testing in combination with track modelling represents an efficient strategy for identification of the current condition of railway track structure and its components. Field investigations for the dynamic characteristics of a railway track and its components were carried out and are presented in this paper. A non-destructive technique using impact excitation, so-called ‘modal testing’, was utilized in these trials. Integrated approach combining field measurements, experimental modal analysis, and finite element modelling to evaluate the dynamic parameters of the in situ railway track components are appended. A ballasted railway track site in Central Queensland managed by Queensland Rail (QR) was selected to perform the field tests. Six sleeper-fastening-rail assemblies were selected for dynamic testing. The frequency response functions (FRFs) were recorded by using Bruel & Kjaer PULSE vibration analyser in a frequency domain between 0 and 1600 Hz. The data obtained were best fitted using the least-square technique to determine the dynamic stiffness and damping constants of the tested track components. In addition, the experimentally determined resonance frequencies along with the dynamic properties of the track components can provide an important input for determining the maximum speed and axle load for the future track upgrades. This paper also points out on how to judge the dynamic responses (e.g. FRFs) together with the visual inspection of existing conditions from the field experience. Examples of testing results representing the deficient integrity are additionally highlighted. Based on the results, the impact excitation technique is an efficient method susceptible to the structural integrity of railway track structures.     

Milling and subsequent thermal annealing effects on the microstructural and magnetic properties of nanostructured Fe90Co10 and Fe65Co35 powders

The influence of milling and subsequent annealing on the microstructural and magnetic properties of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ alloys is investigated. After milling for 8 h a body-centred cubic nanostructured Fe–Co alloy forms with an average crystallite size of about 12 nm. The magnetization saturation (M_S) increases 16% for Fe₆₅Co₃₅ and 5% for Fe₉₀Co₁₀ alloys by milling for 8 h. Subsequent annealing of Fe₉₀Co₁₀ and Fe₆₅Co₃₅ powders for 105 min at 550 °C improves the M_S about 6 and 11%, respectively. Before annealing, the coercivity increases (up to 60 Oe) by milling for 3 h, followed by a reduction on milling for longer periods (45 h). At the initial stage of the heating, a sharp decrease in H_C to 8–10 Oe occurs due to the relief of internal strain. Further heating leads to an increase in the coercivity (intermediate times) followed by a slight diminution on heating for final stage.     

Thermodynamic and kinetic studies of Mg–Fe–H after mechanical milling followed by sintering

The transition metal complex hydride Mg₂FeH₆ has been successfully synthesized utilizing mechanical milling of a 2Mg–Fe mixture followed by heating at 673 K under 6 MPa of hydrogen pressure, without pressing step. The obtained yield of Mg₂FeH₆ was about 50%. Hydrogen storage properties of the Mg–Fe–H system, i.e. capacities, absorption/desorption kinetics and thermodynamic parameters, were examined. The pressure-composition isotherm (PCI) measurements of the samples at 548–673 K showed that the alloys possessed good cyclic stability and reversibility. Enthalpies and entropies of decomposition of the Mg–Fe–H system were evaluated by van’t Hoff plots. The absorption/desorption rates at 573 K were very fast in comparison with the reported data. The non-isothermal desorption of hydrogen was found greatly dependent on the thermal history of the sample.     

Magnetic properties of Ce3−xGdxCo11B4 borides

The structure and magnetic properties of Ce_3−xGd_xCo₁₁B₄ borides have been studied by X-ray powder diffraction (XRPD), magnetization and differential scanning calorimetry (DSC) measurements. X-ray analysis reveals that the compounds crystallize in the hexagonal Ce₃Co₁₁B₄-type structure with P6/mmm space group. The substitution of Gd for Ce leads to an increase of the unit-cell parameter a and the unit-cell volume V, while the unit-cell parameter c decreases linearly. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The Curie temperatures increase as Ce is substituted by Gd. The saturation magnetization at 4 K decreases upon the Gd substitution up to x = 1, and then increases.     

Brush plated ZnS films and their properties

Zinc sulphide thin films were deposited by the brush plating technique using AR grade zinc sulphate and sodium thiosulphate on titanium and conducting glass substrates at a current density of 80 mA cm⁻² and at different deposition temperatures in the range 30–80 °C. The films exhibited cubic structure. Band gap of the films were in the range of 3.79–3.93 eV. Auger spectra of the ZnS films deposited at different current densities indicated that the Zn/S ratio varies in the range of 1.02–1.04. Room temperature PL spectrum of the films deposited at 80 °C indicated two emission peaks at 420 and 480 nm for an excitation of 325 nm. Resistivity of the film varied from 200–769 Ω cm as the deposition temperature increased.     

Electrical d.c. conduction mechanism in some newly synthesized mono- and dipyridine quaternary salts in thin films

The study of temperature dependence of the electrical conductivity and thermoelectric power, for some recently synthesized quaternary salts of bipyridine and indolisine pyridine, is reported. Thin film samples (d = 0.10–0.60 μm) deposited from dimethylformamide solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 290–500 K.The studied organic salts behave as typical p-type semiconductors. The activation energy of electrical conduction laid in the range 1.40–1.75 eV, while the ratio of charge carrier mobilities ranged between 0.77 and 0.93.The correlations between determined semiconducting parameters and specific molecular structure of the compounds have been discussed.In the higher temperature range (360–500 K), the electronic transport in examined compounds can be interpreted in terms of band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model may be conveniently used.     

Far-infrared and galvanomagnetic study of gallium doped PbTe

The far-infrared reflectivity spectra of PbTe(Ga) (N_Ga = 0.1, 0.2, and 0.4 at.%) alloys were measured in the 30–500 cm⁻¹ spectral range at different temperatures and analyzed using a numerical fitting procedure based on the plasmon–phonon interaction model. The three local Ga modes at about 120, 150 and 220 cm⁻¹ together with the strong plasmon–phonon coupling are observed. Using results of galvanomagnetic measurements carrier concentrations and the Fermi level temperature dependence are determined for illuminated and unilluminated samples. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with negative correlation energy. For both, p-type (N_Ga = 0.1 and 0.2 at.%) and n-type samples (N_Ga = 0.4 at.%) the Fermi level is in the forbiden band, but for n-type illuminated sample the Fermi level is in the conduction band at low temperature. Positions and concentrations of different Ga impurity states are obtained using the Gibbs distribution.     

The ultimate sharpness of single-crystal diamond cutting tools—Part I: Theoretical analyses and predictions

In this paper, the brittle–ductile transition lapping mechanism is presented for mechanical lapping of single-crystal diamond cutting tools. The calculated critical depths of cut for controlling brittle–ductile transition in different orientations and on different planes are used to direct tool lapping and deduce the dynamic micro-mechanical strengths (such as tensile, shearing and compressive strengths) of diamond cutting tools, while in the tool fabrication. The investigation illustrates that the dynamic micro-mechanical strengths have great anisotropy, and the strengths in the ‘soft’ direction are all less than those in the ‘hard’ direction on any crystal plane. The lapping of designed cutting tools, oriented (1 1 0)–(1 0 0) and (1 0 0)–(1 0 0) as tool rake and flank faces respectively, is carried out in ductile mode based on the optimal lapping parameters as selected. Both atomic force microscope (AFM) and scanning electron microscope (SEM) measurements results show that the lapping quality of diamond cutting tools is much improved with the proposed lapping approach. The surface roughness on the tool rake face is 0.8 nm (Ra) and lapped cutting edge radius is 35–50 nm as achieved when (1 1 0)–(1 0 0) orientations are selected as rake and flank faces; and the rake face surface roughness is 0.7 nm (Ra) and lapped cutting edge radius is 30–40 nm as the rake and flank faces oriented with (1 0 0)–(1 0 0) combination. Theoretical analyses of the dynamic impact effects on the cutting edge radius are undertaken to predict their ultimate cutting edge radii. Theoretical calculations indicate that the extreme cutting edge radius can be sharpened down to 1–6 nm of the (1 1 0)–(1 0 0) oriented tools, and 2–5 nm for the (1 0 0)–(1 0 0) oriented cutting tools.