Tl System Research Articles

NMR study of high-T c superconductors

From systematic measurements of T c, Knight shift, NQR frequency of 63Cu and 17O with high-pressure measurement in high- T c materials, La 2−xSr xCuO 4, YBa 2Cu 3O 7 and Tl 2 Ba 2 CuO 6+ y the following results have been obtained. The staggered susceptibility at the zone boundary, χ( Q) which is a measure of the antiferromagnetic spin fluctuation decreases in order of the La, Y and Tl system. χ( Q) is governed by the number of Cu d-holes, n(Cu) and O p-holes, n(O) in the CuO 2 plane. χ( Q) increases when n(Cu)/ n(O) increases. T c increases and then decreases with n(Cu)/ n(O) having a maximum at an optimum value of n(Cu)/ n(O). Correlation between χ( Q) and T c has been discussed by assuming χ( Q) to play an essential role for the occurrence of high- T c superconductivity. The T-dependence of 1/ T 1 below T c suggests strongly the d-wave pairing model.

An Experimental Evaluation of the Reproducibility of TLD Systems Using LiF and BeO

Abstract A preliminary report is given on the results of an investigation carried out by four Italian TLD laboratories on the problem of reproducibility of TL systems. Commercial LiF:Mg,Ti chips and BeO discs were chosen as they are the most widely used detectors on personal dosimetry services. Two Harshaw 2000 B + C, one Harshaw 2000-D (Atlas) and two Vinten Toledo readers were used by the participating laboratories. The same set of 30 LiF chips and 30 BeO discs, individually coded, was used, in a sequence, by all laboratories, following a carefully agreed protocol concerning: total number of annealing-irradiation-preheat-readout cycles, irradiation dose, type of source, annealing and preheat procedure, time intervals and reading technique. Five out of the 30 detectors of each type were read without irradiation, to evaluate the background signal of the system. According to a simplified model, the overall variability of a response of a given TL system was assumed to have only two components: (1) the variability really due to the fluctuations of the light output of the detector, per unit dose; and (2) the variability due to the fluctuations of the reader response. Among other results, the present investigation shows that the variability of response of a TL system is primarily due to the instability of the reader.

Temperature dependence of positron annihilation parameters in Tl-Ba-Ca-Cu-O superconductors.

The results of positron lifetime and Doppler broadened line-shape parameter measurements as a function of temperature, across {Tc}, in the Tl-Ba-Ca-Cu-O superconductors are presented. The bulk lifetime in the normal state is found to decrease with the increase in the number of CuO{sub 2} layers. Different temperature dependencies of the annihilation parameters are observed in the various Tl systems containing different numbers of CuO{sub 2} layers. In the Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} system, an increase in lifetime is observed below {Tc}, whereas in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, a decrease in lifetime is seen below {ital T}{sub {ital c}}. In the Tl{sub 2}Ba{sub 2}CuO{sub 6} system, the lifetime is observed to be temperature independent. The different temperature variations of positron annihilation parameters are discussed in the light of the positron density distribution, obtained with use of the results of the self-consistent orthogonalized linear combination of atomic orbitals band-structure calculations. It is argued that the different temperature dependencies of the annihilation parameters is related to the positron density distribution within the unit cell and arise due to local charge transfer in the vicinity of the CuO{sub 2} layer in the superconducting state.

Comparison of interplanar-boson-exchange models of high-temperature superconductivity—possible experimental tests

Semiquantitative tests are considered of models, proposed earlier by this author, in which high Tc superconductivity follows from the exchange of unspecified intermediate bosons (IB) with ω≫ωphonon between fermionic pairs in different CuO2 layers. Earlier predictions of the dependence of Tc(n) on the number n of layers per cluster are extended to include the possibility that Tc(n=1)<∼10 K in the Tl 1201 and 2201 compounds. In common with other authors rapid saturation of Tc(n) with increasing n is found here. Nonetheless, the experimental value of Tc(n=1) in the Tl and Bi systems can play an important role in discriminating between the various models empirically.

Hall effect of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems.

The Hall coefficient ${R}_{H}$ has been measured in Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems as a function of temperature. In all the systems ${R}_{H}^{\mathrm{\ensuremath{-}}1}$ varies linearly with temperature. ${T}_{c}$ decreases as the filling factor \ensuremath{\nu} (${n}_{H}$ normalized to Cu ions present in the unit cell) increases in the Bi and Tl systems. This behavior is opposite in nature to that observed in the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ systems.

Preparation of the bulk superconductor Tl 2Ba 2Ca 3Cu 4O 12

The bulk superconductor Tl 2Ba 2Ca 3Cu 4O 12 with T c (onset) above 112 K has been prepared and structure and chemical composition were examined by X-ray powder diffraction, analytical (EDX) and high resolution electron microscopy. Unit cell dimensions for the tetragonal cell determined by the least squares method are a = 3.853 (1) A ̊ , c=41.98 (3) Å. The transition temperature, T c, of the double layered Tl system increases with the number of Cu-O layers ( n) up to n = 3, while it turns down at n = 4.

Nature of the specific heat anomaly in the Bi and Tl high temperature superconductors

Abstract Specific heat, field cooling Meissner effect, isothermal magnetization, AC susceptibility and resistance were measured on sintered pellets of the Bi and Tl high temperature superconductors with nominal compositions BiPb 0.3 SrCaCu 2 O 5.8 and Tl 2 Ba 2 CaCu 2 O 8 , and for comparison on some pellets of the REBa 2 Cu 3 O 6.9 system. With decreasing field, the field cooling Meissner signals of the Bi and Tl systems approach the same magnitude and transition width (Δ T ≈ 2–3 K) as in high quality pellets of the REBa 2 Cu 3 O 6.9 . The field and temperature dependence of the Meissner signals is analysed in detail. At the transition temperatures of five superconducting phases of the Bi and Tl pellets, the specific heat shows no jumps nor maxima, within the accuracy of the measurement (Δ( C/T ) 2 )). There are however sharp breaks of the slope of C/T at the T c values, which are intrinsically as large as in the REBa 2 Cu 3 O 6.9 . The transitions in the Bi and Tl systems look more like third order transitions rather than like the second order transitions of the REBa 2 Cu 3 O 6.9 .

Superconductivity of Tl-Sr-Ca-Cu-O System in Relation to Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O Systems

It was found that Tl-Sr-Ca-Cu-O system gives rise to at least two superconducting phases, a high-Tc phase at 100 K and a low-Tc phase at about 75 K. The two phases are isostructural to those of Bi-Sr-Ca-Cu-O system. Comparing the Tc's and crystal structures of the Tl and Bi systems, it was suggested that Tc is mainly determined by the combination of two alkaline earth elements, i.e., Sr/Ca or Ba/Ca, when the repetition unit in the layered perovskites is equal.

Electrical conductivity measurements in a Ge-Se-Tl system

The I - V characteristics and dc conductivity measurements of bulk Ge10Se90−xTlx with x = 1 to 9 have been experimentally investigated. The increase in room temperature conductivity is attributed to increase in the percentage of thallium (Tl), which creates charged centers inside the bulk of the material. The decrease in activation energy with increase in thallium content has been discussed on the basis of formation of new charged centers Tl4− (C20)3 in the mobility gap which shifts the Fermi level towards the valence band. An energy band diagram has been suggested on the basis of new charged centers Tl4− (C20)3 and C3+ for a Ge-Se- Tl system.

The binary phase diagrams of thallium with gadolinium, terbium and dysprosium

The TbTl and DyTl systems have been studied by differential thermal analysis, X-ray examination, metallography and microprobe analysis. A reinvestigation of the Gd-TI system has been also carried out in the 35 – 47 at.% thallium composition range. In the TbTl system the following intermetallic compounds exist: Tb 2Tl (decomposes at 1040 °C), Tb 5Tl 3 (m.p. 1290 °C), Tb 5T 13+x, TbTl (m.p. 1300 °C), Tb 3T 15 (decomposes at 1000 °C) and TbTl 3 (m.p. 940 °C). The DyTl system shows the following phases: Dy 2Tl (decomposes at 1190 °C), Dy 5Tl 3 (m.p. 1340 °C), Dy 5Tl 3+x, DyTI (m.p. 1300 °C), Dy 3Tl 5 (decomposes at 1000 °C) and DyTl 3 (m.p. 940 °C). For both systems four eutectics and two peritectics occur. From the reinvestigation of the GdTl system a congruent melting for the Gd 5Tl 3 phase and the existence of a new phase (Gd 5Tl 3+x) have been proposed. The strict analogies between the three systems are discussed and compared with the volume contraction trends.

Ｂｉ系およびＴｌ系層状構造高温超伝導酸化物 超伝導発現機構の解明への鍵

Ｂｉ系およびＴｌ系層状構造高温超伝導酸化物 超伝導発現機構の解明への鍵

木材素材およびＰＥＧ処理材の破壊じん性

Fracture toughness testing was carried out for Japanese beech, castor aralia, ramin, false arbor-vitae, and ramin and false arbor-vitae impregnated with polyethylene glycol (PEG).The main results obtained are summarized as follows:(1) The load-displacement curves had different patterns for different woods.(2) The fracture toughness value of the RL system was larger than those of the TR-RT and TL systems.(3) The fracture toughness value of the wood impregnated with polyethylene glycol was larger than that of the untreated wood.

Phase diagram and magnetic properties of the YbTl system

The YbTl system has been studied by differential thermal analysis (DTA), X-ray examination and metallography. Four intermetallic compounds have been found: Yb 5Tl 2 (decomposes at 1085 ±10 K), Yb 2Tl (decomposes at 1100 ± 10 K), YbTl (melts congruently at 1400 ±15 K) and YbTl 3 (decomposes at 850 ± 5 K). Two eutectics occur: βYbYb 5Tl 2 (at 920 ± 5 K and 16 at.% Tl) and YbTl 3-βTl (at 560 ± 5 K and more than 98 at.% Tl). A eutectoidal reaction is observed at 880 ± 5 K and 10 at.% Tl. The magnetic susceptibility isotherm at room temperature and polytherms in the temperature range 298–800 K are given. Certain peculiarities in the electronic structure and valence state of ytterbium in alloys are discussed. A comparison of the Yb-Tl binary system diagram with those of other Yb-p-element (aluminium, gallium, indium) systems is attempted.

Thermodynamics of mixing in beta alumina - relation to the mixed alkali effect

The energetics of mixing in several binary beta alumina systems have been investigated using thermodynamic techniques. The NaK, -Li, -Ag and -Rb beta aluminas all show energetic stabilizations indicating the presence of some type of cation order. The NaTl system shows quite different behavior with activity coefficients being greater than unity acros the entire system. We have modelled the behavior of the NaK system assuming preferential NaK “ion-pair” formation and find an excellent fit to the activity data. Compositions with X K =0.2 and 0.8 are the most stable, these lie close to the minima observed in the ionic conductivities. In all the systems studied we find a direct correlation between the presence or absence of a mixed alkali effect and the deviation of the mixing energetics from ideality.

The Ge−Tl (Germanium-Thallium) system

The Ge−Tl (Germanium-Thallium) system

Zoning in zircons

The TL emission in many zircons is zoned. Because regions of bright TL emission are anti-correlated with regions of high uranium content, age determination by conventional methods give TL dates which are too low. We designed an image intensifier based TL system capable of resolving features on a 5 micron scale during heating in order to detect zoned grains early in the dating procedure. Early rejection of zoned grains would have made the conventional dating approach feasible. However, although polished crystals can unambiguously be identified as being zoned from their TL images, untreated, whole crystals often have superficial features which tend to blur images of the internal zoned light emissions.

On the relative standard deviation of TLD systems: Experimental verification of a theory

A theoretical model on the relative standard deviation of TL measurements was confirmed by using various TL detectors (LiF, LiF-PTFE, BeO, CaSO 4MMn, CaSO 4:Dy) and by changing the readout parameters. The authors have pointed out that the expected value of the variation coefficient of a TL detector readout system at 1 D LDL is dependent on the background subtraction method, it is, however, always greater than 0.33. The evaluation of various published measurements support the theory published earlier by the authors and indicate that a correct theory on the relative standard deviation of TL systems should incorporate a Poissonian term. The contribution of a Poissonian term in the variation coefficient may be very important for some TL systems. The present model permits the correct estimation of the variation coefficient of even single dose measurements.

Anti-Stokes Raman laser investigations on atomic Tl and Sn

Anti-Stokes Raman laser experiments using metastable atomic Tl and Sn have been performed. The required metastable population inversion is generated by photodissociation of TlI and SnBr2 with KrF laser radiation. The Tl(Sn) system permits frequency up-conversion by 7793 cm−1 (17,163 cm−1). By optimization of system parameters, uv output energies up to 2.5 mJ (377 nm) and conversion efficiencies of more than 25% have been achieved for Tl. Further improvements and principal limitations will be discussed.

Thallium alloys of the rare earth: SmTI Phase diagram and molar volumes of the rare earth thallides

AbstractThe SmTl system has been studied by differential thermal, metallographic and X‐ray analyses. The following intermediate phases were observed: Sm2Tl (decomposes at 1030 ± 10°C); Sm5Tl3 (decomposes at 1060 ± 10°C); SmTl (melting point, 1220 ± 20°C); Sm3Tl5 (decomposes at 940 ± 10°C); SmTl3 (melting point, 870 ± 5°C). Three eutectics occur: β‐Sm—Sm2Tl (840 ± 10°C, 18.0 ± 0.5 at % Tl); Sm3Tl5—SmTl3 (860 ± 5°C, 72.0 ± 0.5 at % Tl); SmTl3—β‐Tl (∼303°C, greater than 99.5 at % Tl); there is an eutectoidal reaction at 760 ± 10°C and 10 ± 1 at % Tl (decomposition of β‐Sm phase). Following crystal structures have been determined or confirmed: Sm2Tl hexagonal hP6—Ni2In‐type, Sm5Tl3 tetragonal tI32—W5Si3‐type, SmTl cubic cI2—W or cP2—CsCl‐type, SmTl tetragonal tP4—AuCu I‐type, Sm3Tl5 orthorhombic oC32—Pu3Pd5 like‐type, SmTl3 cubic cP4—AuCu3‐type.The characteristics of the phase diagram and the molar volumes of the SmTl compounds are compared with those of other RETl alloys and briefly discussed.

Criterion for Mixed Mode Fracture in Wood

The mixed mode fracture failure of eastern red spruce (Picea rubens) was investigated by means of single edge notch and center crack specimens with various crack inclinations in the tangential‐longitudinal plane with propagation in the longitudinal direction (i.e., TL system of crack propagation). These results demonstrate there is a definite interaction between failure stress intensity factors KI and KII during the mixed mode fracture of wood. These mixed mode data were supplemented by the fracture toughness (KIC) and pure mode II critical stress intensity factor (KIIC). Several mixed mode fracture failure criteria were compared. The criterion that could not be rejected is KI/KIC+(KII2/KIIC)=1.