Kh. A. Ziq

XPS and magnetization studies of cobalt sodium silicate glasses

Cobalt sodium silicate glasses with the chemical composition (0.70 - x)SiO2-(0.30)Na2O-xCoO, where 0.0 ≤ x ≤ 0.20, have been investigated by means of X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Co 2p spectra show intense satellite structures ∼ 6 eV above the photoelectron peak and the Co 2p32-Co 2p12 separation was ∼ 15.9 eV for all the samples studied. These observations indicate the presence of high spin Co2+ ions in the glasses. The Co 3p spectra have been fitted with contributions from octahedral and tetrahedral Co2+ and the ratio [Co2+(oct)]/[CoTotal2+] increases with increasing CoO content. The O Is spectra also show composition-dependent changes. The fraction of non-bridging oxygen atoms was determined from these spectra and was found to increase with increasing cobalt oxide. Co(II) ions are found to be incorporated in the glass as network modifiers but the contribution from SiOCo(II) to the non-bridging part of the O Is signal could be separated from that from SiONa by simulating the spectrum. DC magnetic susceptibility measurements were performed on the same samples but these suggest that Co2+ exists mainly in octahedral coordination. The magnetic data indicate that the exchange interaction is antiferromagnetic and increases with increasing CoO in the glass.

Effect of fluorine on the phase formation and superconducting properties of Tl-1223 superconductors

Abstract Fluorination of (Tl 0.5 , Pb 0.5 )Sr 1.6 Ba 0.4 Ca 2 Cu 3 O y high-temperature superconductors has been performed through partial replacement of CuO by CuF 2 in the starting materials. Seven samples with nominal fluorine content x atom per formula unit (0≤ x ≤3.6) were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and magnetization M ( H ) measurements. Fluorine addition has raised the onset transition temperature to 128 K, and increased the critical current density to 300%, the value of the fluorine free sample. XRD, SEM and energy dispersive X-ray (EDX) results showed that the formation of the Tl-1223 phase was enhanced as fluorine was introduced, and the formation of large grains was observed. EDX spot analysis revealed the presence of fluorine as a species of the structure of the Tl-1223 grains. The c -axis of Tl-1223 decreased with increasing x , indicating that fluorine had replaced oxygen in the structure. The behavior of the normal state resistivity with temperature indicated that fluorine addition changed this material from overdoped to optimally doped, and upon further fluorine addition, changes it to slightly underdoped state. That provided an additional evidence that fluorine addition changes the density of charge carrier concentration in the Cu–O planes and improves the superconducting properties of this material.

Solid-state morphology and mechanical properties of Kevlar 29 fiber

Abstract Kevlar 29 is an aromatic polyamide fiber spun from the polymer poly(p-phenylene terephthalamide). It has a paracrystalline structure with a lattice distortion parameter g = 5.9% and an a∗ constant = 0.51. The equatorial x-ray “crystallinity” is 68%; the microparacrystal (mPC) sizes are D 002 = 50 nm, D 110 = 4.4 nm, and D 200 = 3.6 nm. The mPCs are well oriented; the orientation parameter = 0.047. The small-angle x-ray diffraction pattern indicated that the fiber has nc chain folding. It has high tenacity (2.81 GNm−2), close to the tenacity of steel; high Youngs modulus (63.9 GNm−2); small breaking strain (3.8%); and a very high melting point (600°C). Wide- and small-angle x-ray diffraction techniques, differential scanning calorimetry (DSC), and an Amsler tensile tester have been used to characterize the fiber and to assess the effect of annealing on its morphology and mechanical properties.

Structural and magnetic properties of sodium iron germanate glasses

A series of sodium iron germanate glasses, with general composition 0.3Na2O‐xFe2O3‐(0.7 ) x)GeO2 (06 x6 0:15), has been prepared by conventional melting and casting. The chemical states of the various elemental components have been investigated by X-ray photoelectron spectroscopy (XPS) from fracture surfaces produced in situ. The analysis of the Fe 3p core level spectra of the glasses which contain iron oxide revealed the presence of both Fe 2a and Fe 3a oxidation states, with the proportion of the Fe 3a ions found to increase with increasing Fe2O3 content. The O 1s spectra also show composition-dependent changes, with the fraction of non-bridging oxygen atoms also increasing with iron oxide content. Direct current magnetic susceptibility and magnetisation (M) vs magnetic field (H) measurements were also performed on the same samples. The magnetic data support the conclusion that the exchange interaction is antiferromagnetic and increases with increasing Fe2O3 content. The fraction of Fe 2a ions determined from XPS was found to be in good agreement with values obtained from fitting the M vs H data with a standard Brillouin function. ” 2000 Elsevier Science B.V. All rights reserved.

Magnetic properties of praseodymium ions in Na2O–Pr2O3–SiO2 glasses

Sodium praseodymium silicate glasses of nominal composition 0.3Na2O xPr2O3 (0.7� x)SiO2, where 0pxp0:10; have been studied by magnetisation and X-ray photoelectron spectroscopy (XPS). The magnetisation data fail to collapse to a single curve in the M versus H=T representation for all values of x and the spread increases with x; indicating an increase in the magnetic exchange interaction. The M versus H data acquired at different temperatures have been fitted with a Brillouin function by refining the number of Pr 3+ ions in each glass sample. It was found that most of the Pr ions are in Pr 3+ valence state and only a small fraction (p5%) in the Pr 4+ state. Analysis of the XPS line shape indicates only the presence of Pr 3+ ions in these glasses.

Oxygen content and disorder effects on the critical current density in YBa2Cu3Ox

Magnetic measurements have been used to evaluate the critical current density Jc for YBa2Cu3Ox samples with various oxygen content (x) and, for partially oxygenated samples (x~6.5), with different degrees of oxygen disorder. The current density has been expressed in terms (T/Tc)-δ, where δ decreases linearly with x for x<6.6 and becomes constant for 6.6<x<7. Moreover, the variation in Tc with oxygen content has been used to represent Jc as Jc = Jo (x/Tc)-n, where Jo is almost constant and n is temperature dependent. At a given temperature ratio (T/Tc), the oxygen disorder enhances the critical current density and weakens its field dependence. It is argued that the increased number of Cu(1)+3O clusters with increasing disorder may cause additional pinning centres and affect the Jc behaviour.

Magnetic properties of a SiO2-Na2O-Fe2O3 glass and glass ceramic

Abstract A homogeneous SiO 2 –Na 2 O–Fe 2 O 3 glass containing 4.6% Fe 2 O 3 was prepared and devitrified to produce a glass ceramic containing the magnetic compound Na 5 Fe(SiO 3 ) 4 . The DC magnetic susceptibility measurements performed on both samples have shown that the magnetic ion–ion interaction is antiferromagnetic and is stronger in the crystallized sample. It was also shown that M versus H data at different temperatures do not collapse to a single curve in the M versus H / T representation, for either the glass or the heat treated sample. But the spread of the data is larger in the heat treated sample, further indicating a stronger interaction in the crystalline sample. The M versus H curves for the glass sample were fitted with Brillouin function by keeping the total number of magnetic ions constant and varying the proportion of ferrous ions until a best fit was achieved. The [Fe 2+ ]/[Fe total ] ratio obtained from the fit is in good agreement with the value obtained from X-ray photoelectron spectroscopy (XPS) performed on the glass sample.

Magnetization‐vector measurements on a Ni‐Mn spin‐glass alloy

Measurements were made simultaneously of both the longitudinal and transverse magnetization components (M L ,M T ) of a field‐cooled thin‐disk sample of disordered Ni 7 5Mn2 5 as it was rotated quasistatically in various fixed fields (H a ) up to 4 kOe. For H a <1 kOe, the observed behavior at sample‐rotation angles (θ) up to 90° is consistent with a purely unidirectional anisotropy field (H K =0.6 kOe), but at higher θ both M L and M T are anomalously low, signifying that the size of the rotating magnetization vector (M S ) becomes substantially smaller than the thermoremanence. The normal demagnetizing fields are too weak to account for this effect. At higher H a , M S rises slightly above the thermoremanence near θ=90°. This derives from the fact that while M L (θ) is normally behaved, the peak in M T (θ) is anomalously high, indicating that the effective unidirectional anisotropy grows with increasing H a . Moreover, the shape of M T (θ) shows the additional presence of higher‐order (e.g., uniaxial) anisotropy components.

Isothermal anisotropy rotation in a Au‐Fe spin‐glass alloy

Magnetization‐vector measurements were made on a slowly rotating disk sample of Au85 Fe15 after cooling to 4.2 K from above Tg (=52 K) in a 15‐kOe field that saturates the thermoremanence. For MT , the magnetization component transverse to the applied field H, results are shown as HMT vs θ, the sample‐rotation angle relative to H, for θ cycled between 0° and 180° at each value of H. For H≲0.1 kOe, HMT varies nearly reversibly in simple accord with an anisotropy field HK (0.41 kOe in size) that rotates rigidly with the sample. At higher H, the rotational hysteresis grows rapidly until, for H≳0.4 kOe, another simple but highly irreversible behavior is observed. From this behavior, it is deduced that HK rotates relative to the sample isothermally when the torque on it exerted by the sample magnetization reaches the magnitude of a frictional torque. The frictional‐torque coefficient is seen to decrease steadily with increasing H, as confirmed by direct measurements of the rotations of the remanence that resul...

The Effect of Fluorine on the Phase Formation and Properties of Tl-Based Superconductors

Fluorine was found to affect the phase formation and superconducting properties of Tl-based superconductors. By varying x in (Tl0.5Pb0.5)Sr1.6Ba0.4Ca2Cu3OyFx synthesized superconductors, an increase was found in the transition temperature and critical current density. These improvements in the superconducting properties are discussed in terms of partial substitution of fluorine into the oxygen sites which in turn affects the hole doping in this material. Structure, microstructure and elemental analysis by XRD, SEM and EDX techniques are reported; the latter of which shows the fluorine distribution.