Bulk Tl Research Articles

Separation of no-carrier-added Bi and stable Bi from thallium

Abstract No carrier added 204,206Bi radioisotopes were produced by alpha induced reaction on Tl2CO3 target. Liquid liquid extraction method using 18-crown-6 dissolved in nitrobenzene and HClO4 was developed for the separation of NCA 204,206Bi from bulk Tl target. Bulk Tl was observed to be extracted by the organic phase at higher HClO4 concentrations leaving NCA Bi radioisotopes in the aqueous phase. At 0.01 M 18-crown-6 concentration with 2 M HClO4, separation factor (S Tl/Bi) as high as 3.7 × 103 was achieved. The separation experiment was repeated with stable isotopes of Bi and Tl. The extent of separation was monitored by ICP-OES and the results corroborated with radiometric methods.

Dose-rate dependence of natural TL signals from feldspars extracted from bedrock samples

The influence of dose rate on feldspar thermoluminescence shape is considered for a range of natural dose rates. The geologic dose rate experienced by bedrock samples is observed to control the position of the low-temperature edge of the bulk TL signal (the T1/2 parameter), with higher dose rates producing natural TL signals that begin to emit at lower measurement temperatures. This behavior can be explained in terms of the natural equilibrium between electron trapping and detrapping rates, as the trapping rate depends directly on the dose rate. The role of anomalous fading is more subtle. While a wide range of T1/2 values is found at low fading rates, only high T1/2 values are found when the fading rate is greater. This suggests that high fading rates may also influence the natural T1/2 value by making low-temperature regions of the TL curve unstable. Our results illustrate the need to consider dose-rate and fading-rate variations between bedrock samples before interpreting the minimum stability of each natural TL signal, a consequential result for future low-temperature thermochronology applications.

Thermoelectric properties of Tl and I dual-doped Bi2Te3-based alloys

Tl[Formula: see text]Bi[Formula: see text]Te[Formula: see text]I[Formula: see text] (x = 0, 0.05, 0.1 and 0.2) flower-like nanopowders were prepared successfully by the hydrothermal method. Then, the synthesized nanoparticles were pressed into bulks by hot-pressing. The thermoelectric (TE) properties of the Tl[Formula: see text]Bi[Formula: see text]Te[Formula: see text]I[Formula: see text] bulk samples were investigated and discussed. The results showed that the influences of Tl doping on the electrical resistivity and Seebeck coefficients of the Bi2Te3 is over that of I doping. Thus, the power factors of the dual-doped bulks are all less than that of the Bi2Te3 bulk. The thermal conductivities of the Tl[Formula: see text]Bi[Formula: see text]Te[Formula: see text]I[Formula: see text] bulk samples also remain at lower values. As a result, the ZT value of the optimized doped bulk Tl[Formula: see text]Bi[Formula: see text]Te[Formula: see text]I[Formula: see text] attains a value of 1.1 at 398 K.

Separation of no-carrier-added 203Pb, a surrogate radioisotope, from proton irradiated natTl2CO3 target using calcium alginate hydrogel beads

Abstract 203Pb is a promising radioisotope in the field of medical science as an imaging surrogate of 212Pb. In the present investigation 203Pb was produced by proton irradiation of natural Tl2CO3 target and was separated from the bulk Tl target using calcium alginate (CA) hydrogel beads with a high separation factor (3.8×104 at 10−3 M HNO3). During the separation process 203Pb was encapsulated in CA beads and desorption of the radioisotope could only be achieved in 1M HNO3. Possibility of Tl uptake was also checked in Fe doped CA (Fe-CA) beads after oxidation of Tl(I) to Tl(III) by sodium bismuthate. No significant uptake of Tl(III) was noticed in the Fe-CA beads. The matrix is therefore suitable for isolation of 203Pb from the target as well as its storage in the bead for therapeutic as well as diagnostic purpose.

Ionic liquid-salt based aqueous biphasic system for rapid separation of no-carrier-added 203Pb from proton irradiated natTl2CO3 target

Environmentally benign aqueous biphasic systems (ABS) are recognized as green systems in analytical research. In this study, a salt–salt ABS composing of water soluble ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim]Cl) and kosmotropic salt K2HPO4 have been used for the separation of no-carrier-added (NCA) 203Pb from proton irradiated natTl2CO3 target. The optimum separation condition was obtained with 1 min shaking and 10 min settling time of the ABS, where ~60 % of NCA 203Pb was extracted into the IL rich phase with nominal contamination from bulk Tl. The reported separation technique is simple, rapid and meets the demands of green chemistry.

Effect of Sm-substitution on the electrical and magnetic properties of (Tl 0.8Hg 0.2)-1223

Bulk Tl 0.8Hg 0.2Ba 2Ca 2− x Sm x Cu 3O 9− δ superconducting samples with x = 0.00, 0.025, 0.05, 0.10, 0.15, and 0.20 were prepared, in a sealed quartz tube, by a single step solid-state reaction technique. The prepared samples were investigated using X-ray powder diffraction, scanning electron microscope, electron dispersive X-ray, electrical resistivity, ac magnetic susceptibility and electron paramagnetic resonance. Powder X-ray diffraction analysis revealed that the prepared samples are nearly single phase of (Tl, Hg)-1223 with tetragonal structure (space group P/4 mmm). The temperature dependence of the electrical resistivity and the ac magnetic susceptibility was investigated to study the effect of Sm-substitution, on the superconducting transition temperature T c and the intergrain critical current density J c. The data showed a T c suppress as Sm-content increases, whereas J c increases up to x = 0.05, after that it depresses with further increase in x. Furthermore, electron paramagnetic resonance (EPR) spectrum at room temperature was studied for the prepared samples. The values of the gyromagnetic factors, g ⊥, g ∥, the hyperfine structure and the spin density were calculated as a function of Sm-content.

Investigation of odd-order harmonic susceptibilities of a bulk Tl 2Ba 2Ca 2Cu 3O 10 superconductors using critical state approach

The fundamental and high-order harmonic susceptibility, χ n = χ n ′ + i χ n ″ ( n = 1 , 3 , 5 and 7) were measured as a function of temperature (50–130 K), frequencies (11 and 140 Hz) and AC magnetic field amplitude (80–1280 A/m) on a bulk Tl 2Ba 2Ca 2Cu 3O 10 high- T c superconductor prepared by the solid-state reaction method. They exhibit dependence on the amplitude of the AC field. The observed dependences were analyzed by using the Bean Model. We have obtained an empirical function for the penetration field H p = H α ( 1 - t ) β , with t = T / T cb . Best fitting to data was obtained with parameters H α ≈ 2.6 × 1 0 4 A / m and β = 1.74 . The experimental values agree well with the theoretical findings. The XRD pattern, resistivity measurement and SEM analysis were also carried out to characterize the sample.

Ultrasonic Velocity Studies on Tl2Ba2Ca2Cu3O10 Superconductor

Ultrasonic longitudinal and shear velocities propagated at 7–10 MHz in bulk Tl 2 Ba 2 Ca 2 Cu 3 O 10 have been measured between 80 K and 300 K. Shear velocity measurements revealed a pronounced slope discontinuity of 421 ppm/K at around 160 K. A similar slope change was not observed in the longitudinal mode. The slope change around 160 K for the shear mode is suggested to be attributed to some form of correlated Tl and O(4) orderings in the material.

Influence of the mass density on the critical current density of the bulk Tl 2Ba 2Ca 2Cu 3O 10 material

The influence of the mass density of bulk Tl 2Ba 2Ca 2Cu 3O 10 sample on its critical current density is investigated. An empirical relationship between the sample density and the transport critical current density was found and this relationship can be explained by assuming that the intergranular critical current is approximately inversely proportional to the average linear separation of the grains.

MOCVD routes to Tl-2212/MgO/Tl-2212 trilayers — preliminary observations on growth and microstructural/electrical properties

The suitability of Tl 2Ba 2CaCu 2O 8 (Tl-2212) and MgO for growing SIS trilayers by metal-organic chemical vapor deposition (MOCVD) is examined. Low temperature (500°C) epitaxial (100) MgO film growth on (110) LaAlO 3 by MOCVD using Mg(dpm) 2 (dpm=2.2.6.6-tetramethyl-3,5-heptanedionate) is demonstrated. Tl-2212 does not decompose under these MgO growth conditions, although decomposition occurs at lower O 2 partial pressures. To form trilayer structures. BaCaCuO(F) films are first grown on (110) LaAlO 3 by MOCVD using Ba(hfa) 2 · mep (hfa=1,1,1,5,5,5-hexafluoropentane-2,4-dionate; mep=2,5,8,11,14,17-hexaoxanonadecane), Ca(hfa) 2 tet (tet=2,5,8,11,14-pentaoxapentadecane) and Cu(dpm) 2 precursors and are then post-annealed in the presence of bulk Tl 2Ba 2CaCu 2O N to form Tl-2212. MgO is then deposited by MOCVD. Finally, a top TBCCO layer is grown by MOCVD and subsequent Tl 2O anneal to complete the trilayer. Both of the TBCCO layers are highly oriented, while the MgO layers are largely polycrystalline due to the rough underlying Tl-2212. Both TBCCO layers are superconducting ( T c ∼ 105 K).

In-situ STM investigation of Tl and Pb underpotential deposition on chemically polished Ag(111) electrodes

In-situ STM was used to investigate the adlayer formation and structure of Tl adsorbates at chemically polished Ag(111) electrodes in perchlorate electrolyte, and to study the effect of extended polarization of incomplete Tl and Pb adlayers at high initial adsorbate coverage. In the Tl+/Ag(111) system, the full first monolayer adsorbate has a hexagonally close packed structure with interatomic distances that are compressed in comparison with the bulk Tl phase. The subsequently formed second monolayer has also a hexagonally close packed (hcp) structure, but shows more pronounced disordered domains. Incomplete first Tl monolayers of high coverage have the same hcp structure as a complete monolayer, but do not extend to the very boundary of the substrate terrace. Extended polarization of such monolayers leads to a conversion of the original hcp layer into a coverage with [√3 × √3]R30 °—symmetry which is interpreted as a mixed coverage, where every third Ag atom is replaced by a Tl atom. Similar phenomena are observed during long-time polarization of an incompletely formed Pb-coverage. The results are discussed with regard to the role of the atomic steps and reveal the importance of surface singularities for the understanding of the adsorption behaviour at real electrodes.

Structure of electrodeposited Tl overlayers on Au(100) studied via surface X-ray scattering

The electrodeposition of Tl on Au(100) has been investigated using surface X-ray scattering. At potentials prior to Tl bulk deposition, Tl adatoms form a c( p × 2) close-packed monolayer on the unreconstructed Au(100) surface in both acid and alkaline solutions. The Tl monolayer uniaxially compresses over a 0.25 V wide potential range and the nearest-neighbor-separation of Tl attains a minimum value of 3.34Å. This is close to the value obtained on Au(111) prior to bulk Tl deposition. From the specular X-ray reflectivity, a 2.55ÅAu Tl layer spacing is obtained for the c( p × 2) monolayer. Bulk deposition of Tl at potentials negative of the reversible Nernst potential results in the formation of imperfectly-aligned hexagonal-close-packed crystallites on top of the c( p × 2) monolayer. At potentials positive to the stripping of the c( p × 2) monolayer, a (2 × 2) diffraction pattern is observed in perchloric and sulfuric acid solutions but not in alkaline solutions. Real space models are proposed.

Structure of metal adlayers during the course of electrocatalytic reactions: O 2 reduction on Au(111) with Tl adlayers in acid solutions

Surface X-ray scattering has been used to determine the structure of Tl adlayers on the Au(111) electrode surface during the course of O 2 reduction in acid solution. O 2 reduction is considerably catalyzed by Tl adlayers on Au(111). The half-wave potential is shifted to more positive values in the presence of the Tl adlayer. In the potential region between −0.18 and −0.4V (vs. sce), the reaction mechanism changes from a 2e-reduction on Au(111) to a 4e-reduction on Au(111) covered with a lowcoverage Tl phase. The close-packed rotated-hexagonal Tl phase, which exists in the potential range between −0.4V and the bulk Tl deposition at ~ −0.7V, has a lower activity for O 2 reduction than the low-coverage phase. O 2 reduction does not change the Tl coverage in this phase but causes a significant decrease of the in-plane diffracted intensity. This observation indicates that the O 2 molecules interact directly with the Tl adatoms prior to the charge transfer. It provides the most direct evidence that the outer sphere charge transfer mechanism is not operative for some surfaces. H 2O 2 reduction is facile on the surface covered with the low-coverage Tl phase, while it is almost completely suppressed by the rotated-hexagonal phase.

Effect of silver addition on the single-layer Tl superconductors

The effect of silver additions, to bulk Tl 0.5Pb 0.5Sr 2CaCu 2O 7-δ-Ag x ( x=0.0, 0.008, 0.016, 0.1, 0.37, and 1.0) superconductor, on microstructure and electrical properties were studied. A Eutectic-like reaction between (Tl-1212 + Ag) was observed. In the case of x = 0.37, liquid phase was formed at 830°C resulting in enhanced densification & grain growth. Changes in T c with silver content were observed, but the presence of silver does not cause any change in the intragranular J c values, which was on the order of 10 6 A cm 2 at 40K in self field.

Relationship between grain connectivity, alignment, and critical current density in high-temperature superconducting bulk materials

Uniaxial hydraulic pressure was successfully employed to partially reorient the c-axes of the highly anisotropic superconducting grains in bulk Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9−δ samples. The partial reorientation was confirmed by X-ray diffraction pattern, rocking curves, and SQUID magnetization measurements. Samples made from the superconducting powder with partial alignment in c-axis direction and samples made from reaction mixture (in-situ synthesis method) with random orientation should have a similar grain connectivity since both were made by the same fabrication procedure. Both types of samples were found to exhibit about the same J c value of 15 000–17 000 A/cm 2 at 77 K. By contrast, another pair of samples with the same c-axis alignment as shown by X-ray diffraction, rocking curve, and SEM measurements, but with different grain connectivity due to the different compression and heat treatment procedure used, showed a significant difference in J c. The just rolled tape had a J c of 13 300 A/cm 2, whereas the rolled and subsequently compressed tape had a J c of 19 500 A/cm 2 at 77 K. Based on the results of these and other related experiments, we have to conclude that grain connectivity, not lattice alignment, is the decisive factor in determining the J c of Tl based 1223 bulk superconducting materials and silver-sheathed superconducting tapes made by the powder-in-tube method.

Effect of Cr and V substitution on the properties of bulk Tl-based superconductors

Bulk TlBaCaCuO superconducting samples have been used to analyse the effect of Cr and V doping on the intergranular properties. The a.c. magnetic susceptibility has been measured as a function of temperature and a.c. magnetic field amplitude up to 14 000 A m −1 as well as the resistivity as a function of temperature and d.c. applied magnetic field up to 795 kA m −1. For the samples doped with Cr an enhancement in the intergranular critical current density was observed; the sample doped with V gave results similar to those obtained for the undoped Tl compound. The role of Cr and V in these materials is discussed in terms of the electrical and magnetic measurements performed. Additionally, measurements of the resistance versus temperature and applied d.c. field may help to elucidate the behaviour of the irreversibility line in these Tl compounds.

Underpotentially deposited thallium on silver (111) byin situsurface x-ray scattering

Using in situ surface x-ray scattering, we have investigated the atomic structure, the stability, and the dependence of the structure on electrode potential for electrochemically deposited Tl monolayers and bilayers on Ag(111). The layers were formed by underpotential deposition (UPD) at electrode potentials positive of the reversible potential for bulk Tl deposition. At potentials between -475 and -680 mV (versus Ag/AgCl), the Tl deposit forms an incommensurate, hexagonal two-dimensional (2D) monolayer that is compressed relative to bulk Tl by 1.4--3.0 % and rotated from the Ag [011\ifmmode\bar\else\textasciimacron\fi{}] direction by \ensuremath{\Omega}=4\ifmmode^\circ\else\textdegree\fi{}--5\ifmmode^\circ\else\textdegree\fi{}. The structure of the monolayer does not change over at least 24 h (the longest we waited). From diffraction scans of the Tl Bragg rods, we find that the in-plane and vertical root-mean-square displacement amplitudes are 0.36\ifmmode\pm\else\textpm\fi{}0.1 and 0.46\ifmmode\pm\else\textpm\fi{}0.1 \AA{}, respectively.The monolayer structure is the same as that of vapor-deposited Tl/Ag(111), and this shows that the interaction between the solvent molecules and the Tl adatoms does not influence the monolayer structure. Since the monolayer has a structure that is about the same as the closest-packed planes of bulk Tl, we deduce that the adatom-adatom interactions are the most important structure-determining forces. The compression of the monolayer (compared to bulk Tl) is explained in terms of effective-medium theory. With decreasing electrode potential, the in-plane spacing between Tl adatoms decreases and this permits a calculation of the 2D compressibility. This decreases with atomic spacing, but has an average value ${\mathrm{\ensuremath{\kappa}}}_{2\mathrm{D}}$=1.54\ifmmode\pm\else\textpm\fi{}0.10 A${\mathrm{\r{}}}^{2}$/eV, which is similar to previously measured compressibilities of UPD monolayers and is in reasonable agreement with theoretical estimates. The rotation angle \ensuremath{\Omega} depends on electrode potential and adatom spacing, but irreversibly decreases with potential cycling (which is possibly due to the adsorption of trace impurities). Despite this irreversibility, the dependence of \ensuremath{\Omega} on adatom spacing qualitatively agrees with theory. We have investigated the structure of monolayers where the deposition potential is reached in either an anodic or cathodic scan and found these structures to be identical. This shows that the monolayer is in thermodynamic equilibrium and that the finite width and offset of the peaks in the deposition curves are due to kinetics, the influence of adsorbed anions, and/or substrate heterogeneity. At potentials between the monolayer region and bulk deposition, Tl forms a bilayer and this also has a hexagonal structure that is incommensurate with the Ag(111) substrate. In the bilayer, the compression is 1.0% (compared to bulk Tl) and the rotation from the Ag [011\ifmmode\bar\else\textasciimacron\fi{}] direction is 3.9\ifmmode^\circ\else\textdegree\fi{}; these are both less than in the monolayer.

Nuclear specific heat of thallium

We have measured the nuclear specific heat of a 0.79 mole thallium sample of 5 N+ purity in the temperature range 70 µK≤T≤20 mK and in magnetic fields from 20 mT≤B≤228 mT. The experimental results agree with the theoretical expectation for the specific heat of a nuclear paramagnet with the properties of Tl. Our results for the nuclear specific heat imply that the static properties of bulk Tl seem to differ from the dynamic, surface-sensitive properties of Tl samples investigated in former nuclear magnetic resonance experiments.

1⧸ƒ noise power measurements on Tl 2Ba 2Ca n−1 Cu nO 4+2 n ( n = 2 and 3)

We have performed systematic 1⧸ƒ noise power measurements on bulk Tl 2Ba 2Ca n−1 Cu n O 4+2 n ( n = 2 and 3) materials normal and superconducting states. The 1⧸ƒ noise power is generally found to decrease with temperature until the superconducting transition region is approached. We observe no correlation between the magnitude of the 1⧸ƒ noise power in the normal state and the sample quality. In contrast to bulk Y 1Ba 2Cu 3 O 7− δ samples, the enhancement of the 1⧸ƒ noise in the superconducting transiti on region is reduced or even totally disappears in some of our good quality samples. We discuss a model calculation based on potential fluctuations in the grain boundary regions modeled as metal-insulator-metal junctions. We demonstrate that if direct knowledge of the barrier characteristics of the junctions is available, it is possible to explain our experimental data quantitstively.