S. A. Halim

AC susceptibility study in Bi1.6Pb0.4Sr2(Ca1−xNdx)2Cu3Oδ ceramic superconductors

Abstract We have studied the frequency dependence of the AC susceptibility in polycrystalline samples of Bi1.6Pb0.4Sr2(Ca1−xNdx)2Cu3Oδ. AC susceptibility measurements in the range 20–1000 Hz show that as the frequency increases, the intra and intergranular AC loss peaks move to higher temperature, and also the height and the width of the peaks increase. When we plot the peak height as a function of the AC field amplitudes, we observe a valley-like behavior. We qualitatively discuss experimental results in the framework of the critical state model, estimate the effective volume fraction of the grains and determine the temperature dependence of the intergranular critical current density by means of the best fit of the calculated data for the experimental matrix susceptibility. Since the granularity effect was very pronounced at low field range, we separated the contribution of the grains and matrix from the total measured AC susceptibility.

Thermal diffusivity measurement of Zn, Ba, V, Y and Sn doped Bi-Pb-Sr-Ca-Cu-O ceramics superconductors by photoacoustic technique

The simple open photoacoustic cell technique is demonstrated for measuring the thermal diffusivity of the Zn, Ba, V, Y and Sn doped Bi-Pb-Sr-Ca-Cu-O superconducting ceramic samples. It is based upon the measurement of the photoacoustic signal as a function of the modulation frequency in the region where the sample thickness, ls, equal to the thermal diffusion length of the sample, μs. The obtained thermal diffusivity values of Ba, V, Y and Sn doped in Bi-Pb-Sr-Ca-Cu-O system increase with the increasing dopant concentration at Ca side. However, the thermal diffusivity values of Zn doped sample decrease with the increasing of dopant concentration in the system. The measured thermal diffusivity value was found to be very dependent on the dopant atom and dopant concentration.

Effect of barium doping in Bi–Pb–Sr–Ca–Cu–O ceramics superconductors

Abstract The effect of barium doping on the superconductivity in Bi 2 Pb 0.6 Sr 2 Ca 2− x Ba x Cu 3 O δ system has been investigated by resistivity, ac susceptibility measurements and X-ray diffraction analysis. Barium was incorporated in the calcium site with x ranging from 0.00 to 0.10. The temperature dependence of electrical resistance and ac susceptibility measurements were made on these samples. The nature of the temperature dependence of the resistance curves indicates the presence of a superconducting transition between grains coupled by weak links. From the XRD data, it is observed that the volume percentage of the 2223 phase decreases with the increasing barium concentration. The presence of low T c phase is also visible in the real component, χ ′, of the susceptibility data, while the imaginary component, χ ″, show a shift towards lower temperature in the intergranular coupling peak, T p , as the barium concentration increases. Barium doping does not enhance the T c zero but gradually decreases its value from 104 K to 88 K for x =0.00 to x =0.10 respectively.

Structural, morphology and electrical properties of layered copper selenide thin film

Thin films of copper selenide (CuSe) were physically deposited layer-by-layer up to 5 layers using thermal evaporation technique onto a glass substrate. Various film properties, including the thickness, structure, morphology, surface roughness, average grain size and electrical conductivity are studied and discussed. These properties are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ellipsometer and 4 point probe at room temperature. The dependence of electrical conductivity, surface roughness, and average grain size on number of layers deposited is discussed.

STRUCTURE, ELECTRICAL TRANSPORT AND MAGNETO-RESISTANCE PROPERTIES OF La5/8Ca3/8MnO3 MANGANITE SYNTHESIZED WITH DIFFERENT MANGANESE PRECURSORS

We synthesized the polycrystalline manganite of La5/8Ca3/8MnO3 with three different manganese routes prepared through a solid state reaction method. The effects of the manganese route selection on the structure, electrical transport and magneto-transport properties were examined in this study. The samples were characterized using X-ray diffraction (XRD) and SEM to identify their structure and morphology. XRD analysis confirmed that all samples were in single phase with orthorhombic structure and belonged to the Pnma space group. The average grain sized samples with manganese route of Mn2O3 and MnCO3 had a grain size of 1.2–8.7 μm and 2–7.5 μm, respectively. For the MnO2 route, the sample had a small melt-like shape with higher porosity. The metal–insulator transition temperature, TMI, for LCMO (Mn2O3), LCMO (MnO2) and LCMO (MnCO3) samples were 270 K, 266 K and 258 K, respectively. All the samples showed negative magneto-resistance with significant increase in value near the TMI temperature. The highest CMR (colossal magneto-resistance) ratio was found in LCMO (Mn2O3), -22.06% at 270 K, followed by -16.69% for LCMO (MnO2) at 80 K, and 15.2% for LCMO (MnCO3) at 100 K in a 1 T magnetic field.

ac losses in Ni-doped Bi1.6Pb0.4Sr2(Ca1-xNix)2Cu3Oδ ceramic superconductors

The complex ac susceptibility was measured as a function of temperature and ac field amplitude on rectangular bar shaped high-temperature superconductors with nominal composition of Bi1.6Pb0.4Sr2(Ca1−xNix)2Cu3Oδ (x = 0–0.10) superconducting samples prepared by the solid state reaction method. It is found that as the amount of Ni doping increases, the critical temperature Tc slowly decreases. A small amount of Ni doping (x = 0.03) increases the intergranular critical current jcm and the flux pinning of the Bi(Pb)-2223 system. The effective volume fraction of the grains and the field dependence of the intergranular critical current density were estimated by comparison of the maximum of the extracted matrix susceptibility and the corresponding calculated data which was obtained from hysteresis losses employing the power law critical state model.

Effect of Sm-Doping on Magnetic and Dielectric Properties of BiFeO3

Polycrystalline Bi1-xSmxFeO3 multiferroic samples in the range 0 ≤ x ≤ 0.1 were prepared via solid state reaction method. The effect of samarium ion (Sm3+) doping at the bismuth site in multiferroic BiFeO3 structure and its relation with magnetic and dielectric properties were investigated. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and Impedance Analyzer were used to characterize the structure and the properties of the composition. The XRD results showed that all the compounds are rhombohedral distorted perovskite structure (R3C). The average grain size identified by SEM were 2.61 µm and decreased to 1.18 µm by introducing the element of Sm doping. At room temperature, all samples showed a spontaneous magnetization which was enhanced by doping with Sm3+ ion. The dielectric constant and dielectric loss decreased inversely proportional to the frequency from 102 to 106 Hz.

Study of Nd substitution in Bi–(Pb)–Sr–Ca–Cu–O high-Tc superconductors

Abstract Measurements of complex AC susceptibility χ=χ′+χ″ as a function of temperature and AC field amplitude have been carried out on rectangular bar-shaped high-temperature superconductors with nominal composition of Bi1.6Pb0.4Sr2(Ca1−xNdx)2Cu3Oδ superconducting samples prepared by the solid-state reaction method. The effect of Nd-substitution on the Bi–(Pb)–Sr–Ca–Cu–O system has been investigated in terms of an AC susceptibility study. It was found that as the amount of Nd content x increases, the transition temperature decreases. Temperature-dependent critical current density was deduced from AC susceptibility data. In spite of a slight decrease of Tc, the highest pinning strength parameters (Jcm (T=0) and temperature exponent n) were obtained for the sample with x=0.02.

Growth and characterization of ZnO multipods on functional surfaces with different sizes and shapes of Ag particles

Three-dimensional ZnO multipods are successfully synthesized on functional substrates using the vapor transport method in a quartz tube. The functional surfaces, which include two different distributions of Ag nanoparticles and a layer of commercial Ag nanowires, are coated onto silicon substrates before the growth of ZnO nanostructures. The structures and morphologies of the ZnO/Ag heterostructures are investigated using X-ray diffraction and field emission scanning electron microscopy. The sizes and shapes of the Ag particles affect the growth rates and initial nucleations of the ZnO structures, resulting in different numbers and shapes of multipods. They also influence the orientation and growth quality of the rods. The optical properties are studied by photoluminescence, UV-vis, and Raman spectroscopy. The results indicate that the surface plasmon resonance strongly depends on the sizes and shapes of the Ag particles.

The Synthesis and Characterization of Peach-Like ZnO

Peach-like ZnO microstructures are synthesized using vapor phase transport on MgO (001) substrates with a copper oxide (60 nm) buffer layer. The structure and morphology of the product are investigated using an x-ray diffractometer (XRD) and a field-emission scanning electron microscope. The peaches have an average diameter of 3 ?m and a wurtzite structure. To study the optical properties, photoluminescence (PL) and Raman spectroscopy are employed. A strong UV emission at 380 nm in the PL spectra is observed, and a sharp and dominant peak at 437 cm?1 in the Raman spectrum can be assigned to the good crystallization of obtained product. In addition, the growth mechanism of the peach-like ZnO structure is tentatively investigated based on the EDX analysis and growth time.