Li For Cu Research Articles

Crystallographic, optical, and electronic properties of Li-doped CuIn(S,Se)2, (Cu,Li)In(S,Se)2

(Cu1−xLix)In(S1−ySey)2 (CLISSe) samples with 0.0 ≤ x ≤ 0.4 and y = 0.25, 0.50, and 0.75 were prepared by a mechanochemical process and sequential heating. The X-ray diffraction (XRD) peaks of the (Cu1−xLix)In(S1−ySey)2 shifted to the lower angle side by the substitution of Li atoms for Cu atoms. The solid solution limit of Li for Cu in (Cu1−xLix)In(S1−ySey)2 system widened with increasing Se content, y. The single-phase (Cu1−xLix)In(S1−ySey)2 samples were obtained for the compositions with 0.0 ≤ x ≤ 0.05 for y = 0.25, 0.0 ≤ x ≤ 0.20 for y = 0.50, and 0.0 ≤ x ≤ 0.30 for y = 0.75. The crystallographic parameters such as the lattice constants a and c, c/a, and the atomic coordinate of a S/Se atom for (Cu1−xLix)In(S1−ySey)2 were refined by Rietveld analysis using XRD data. Both the lattice constants a and c of the (Cu1−xLix)In(S1−ySey)2 with a tetragonal chalcopyrite structure increased with increasing Li content, x. The band gaps of (Cu1−xLix)In(S1−ySey)2 solid solutions widened with increasing Li content, x. To understand the band diagram of the solid solutions, the energy level of the valence band maximum (VBM) from the vacuum level was determined from the ionization energy measured by photoemission yield spectroscopy (PYS). The energy level of the conduction band minimum (CBM) was also determined by adding the band-gap energy to the VBM level. The VBM level of the (Cu1−xLix)In(S0.25Se0.75)2 solid solution decreased considerably with increasing Li content, x. The CBM level of the (Cu1−xLix)In(S1−ySey)2 solid solution was approximately constant. The Li doping in CuIn(S,Se)2 is useful for decreasing the VBM of the CuIn(S,Se)2 absorber and increasing the band-gap energy of the CuIn(S,Se)2 absorber without increasing the CBM level.

Superconductivity in Co doped Cu 0.5Tl 0.5Ba 2(CaM)Cu 2.95Co 0.05O 10− δ (M = Mg, Be) samples

We have investigated the possible source of suppression of superconductivity in Cu 0.5Tl 0.5Ba 2Ca 2Cu 2.95Co 0.05O 10− δ samples. We substituted Mg ( r = 0.65 Å) and Be ( r = 0.31 Å) at Ca ( r = 0.99 Å) sites in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) superconductor to enhance inter-planar coupling and Li in the charge reservoir layer (Cu 0.5Tl 0.25Li 0.25)Ba 2O 4− δ to supply extra carriers to CuO 2 planes. It was observed that zero resistivity critical temperature is decreased after Mg and Be substitution in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ samples. However, the c-axis lattice parameter is increased in both samples in spite of smaller ionic radius of Mg and Be as compared to Ca. However, in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) samples we have achieved enhanced superconductivity by Li doping. It was observed from these studies that cobalt doped in the conducting CuO 2 planes somehow localizes the carriers at Co 3+ sites and decrease the density of mobile carriers. But Li in Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer supplies the required number of carriers to the CuO 2 planes; therefore, the critical temperature is increased in Li doped samples.

Thermodynamic evaluation of Cu–Li phase diagram from EMF measurements and DTA study

Two experimental techniques were used in investigations of the Cu–Li system. An electrochemical concentration cell method was applied in measurements of activities of Li in Cu–Li alloys while DTA measurements were performed for liquidus and solidus determination. Activity measurements were conducted using electrochemical cells with the liquid LiCl–LiF and LiCl–KCl electrolyte in the concentration range from X Li = 0.05 –0.7 for 20 alloys and at temperatures between 633 K (360 ∘C) and 923 K (650 ∘C). DTA experiments were performed by derivatograph Q-1500 (Paulik–Paulik–Erdey system) for 17 alloys with concentration changing from X Li = 0.18 to 0.975. The analyses of temperature dependencies of the electromotive force (EMF) for different concentrations of Cu–Li alloys indicated the existence of a new Cu 2Li 3 entropy-stabilized intermetallic phase. Using all available DTA literature data of Pastorello [S. Pastorello, Gazz. Chim. Ital. 60 (1930) 988–992] and Klemm and Volavšek [W. Klemm, B. Volavšek, Z. Anorg. Chem. 296 (1958) 184–187] and those from EMF and DTA measurements of this work the optimization and calculation of the Cu–Li system were performed. Finally, the thermodynamic properties of the fcc-(Cu), Cu 2Li 3 intermetallic phase and the liquid phase were established together with a new proposed phase diagram of the Cu–Li system. The heat of formation of Cu 2Li 3 compound established during the optimization of Cu–Li system is tentative and it should be experimentally confirmed or corrected in future investigations.

Supersaturated Cu–Li solid solutions produced by mechanical alloying

In the present work the effect of milling parameters, such as the ball-to-powder ratio and milling time, on the formation of supersaturated Cu–Li solid solutions produced by mechanical alloying was investigated. The microstructural changes and the phases present after milling were analyzed using scanning electron microscopy and X-ray diffraction, whereas the amount of lithium was measured by atomic absorption spectroscopy. The results show that the solubility limit of Li in Cu can be extended up to a maximum value of 17 at.%. It was also observed that the lattice parameter of the copper matrix and the microhardness of the as-milled powder both changed as a function of the lithium content.

Structural, magnetic, and transport properties of La2Cu1-xLixO4.

Li substitutes for Cu in La{sub 2}CuO{sub 4} up to the limiting stoichiometry La{sub 2}Cu{sub 0.5}Li{sub 0.5}O{sub 4}, which has superstructure order. The effects of this in-plane hole doping on the structural and magnetic properties of La{sub 2}CuO{sub 4} are very similar to those due to Sr substitution. The tetragonal-orthorhombic structural phase transition occurs, for a given amount of Sr or Li, at nearly the same temperature, and the in-plane lattice constant of La{sub 2{minus}{ital y}}Sr{sub {ital y}}Cu{sub 1{minus}{ital x}}Li{sub {ital x}}O{sub 4} at room temperature depends only on the combined hole count ({ital x}+{ital y}) and not on the individual Sr or Li concentration. Long-range magnetic order is destroyed upon substituting 3{percent} Li for Cu, analogous to the effect of Sr substitution on {ital T}{sub N{acute e}el}. However, the holes introduced by Li substitution are bound. The resistivity as a function of temperature is nonmetallic for all Li concentrations. {copyright} {ital 1996 The American Physical Society.}

Unusual elastic properties of pure and doped La2CuO4 as probed by resonant ultrasound spectroscopy.

La2CuO4 undergoes a structural phase transition from tetragonal to orthorhombic crystal symmetry as it is cooled below 525 K. Hole-doping the material (for example, by substituting Sr for La or Li for Cu) rapidly suppresses the structural transition temperature. Additionally, the in-plane lattice constant of La2−xSrxCu1−yLiyO4 is a function only of the combined hole count (i.e., x+y) and not of the individual Sr and Li concentrations. RUS measurements for stoichiometric, Sr-doped, and Li-doped La2CuO4 have been used not only to map out the phase diagram of this system but also to reveal the unconventional nature of the transition. These results suggest a strong coupling between hole concentration and structural properties as well as a large in-plane/out-of-plane anisotropy.

Effect of the local substitution of Li for Cu on the electronic structure of YBa 2Cu 3O 7

The change of the electronic structure of YBa 2Cu 3O 7 caused by the local substitution of Li for Cu has been studied by the recursion method. The characteristics including the partial wave density of state, the types and intensities of bonds, and the valence on a site etc. are obviously affected by Li on the replacing site and its neighbours. In the case of the substitution of Li for the Cu(2) site, the two-dimensional character of the electronic structure in CuO 2 planes is locally destroyed, accompanied by the migration of electrons or holes, which causes the decrease of the hole concentration in the CuO 2 planes. The local substitution of Li for Y has also been discussed. This substitution can strengthen the two-dimensional character of the carriers in the CuO 2 planes. From our point of view, these changes may be responsible for the changes of T c in the Li-doped YBa 2Cu 3O 7 material.

Effects of some additional elements on the reaction diffusion in high-Tc oxide composites

The reaction diffusion between a substrate of high melting point and a coating layer of low melting point produces a thick superconducting layer with a uniform composition. The addition of Ag to the coating layer enhances the diffusion in both Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems. The Ag is pushed out from the superconducting layer to the surface of the specimen, forming a laminated structure composed of a superconducting layer and an Ag layer. This movement of Ag improves the grain orientation in the superconducting layer. Meanwhile, the substitution of Li for Cu in the coating layer of the Bi-Sr-Ca-Cu-O system significantly promotes the diffusion, and a Tc of 85 K is obtained after the reaction at 780 degrees C for 30 min.

Li substitution in the Bi 2Sr 2Ca 1Cu 2O 8 superconductor

The T c value of the Bi 2Sr 2Ca 1Cu 2O 8 superconductor (2212-phase or BSCCO) rises with the substitution of Li for Cu. For the nominal composition of Bi:Sr:Ca:Cu:Li = 2.2:1.8:1.05:1.45:0.7, almost single 2212-phase is obtained by sintering at low temperature, 740°C, followed by quenching to room temperature. The samples shows a T c,zero of 91 K in the resistance-temperature ( R- T) curve and a T c,on of 92 K in the Meissner effect. Both Ar annealing and O 2 annealing make the R- T curve semiconductive. The results of X-ray diffraction measurements, electron microscopy and elemental analysis on this sample indicate that the Li ion occupies the Cu site.

Partial substitution of Li for Cu in superconducting YBa2Cu3Oy

0.33–33% of the Cu in superconducting YBa2Cu3O y has been replaced by Li (i.e.,x=0.01–1 in single-phase or nominal YBa2Cu3−x LixOy). X-ray diffraction powder patterns remain the same as for YBn2Cu3O y , with identical patterns up to about 17% substitution (i.e.,x=0.5). At higher percentages an additional phase appears. Electrical conductivity measurements indicate a small elevation ofT c at low Li content. Starting at about 5% Li (x=0.15),T c declines progressively and its width increases asx is raised.

Self-Sustaining Coatings for Fusion Applications - Copper Lithium Alloys

Dilute binary alloys have been discussed previously as a means of producing self-sustaining coatings for fusion applications. The anticipated advantages of such coatings are described in a companion paper.11 Issues addressed in this paper concern experimental observation of the formation of a low-Z coating by solute segregation in a Cu-Li alloy, maintenance of the coating in a sputtering environment, and a comparison of the calculated net erosion for W, Mo, and Cu-Li when used as either the divertor plate or the bottom limiter for INTOR.Auger electron spectroscopy has been used to monitor the surface composition of an alloy consisting of 3.0 at.% Li in Cu while sputtering with 1–3 keV Ar+ or He+ at a flux of 1012 – 1014 cm−2 sec−1 (corresponding to a gross erosion rate of several mm/yr) at temperatures up to 430°C. It is found that the alloy is capable of reproducibly maintaining a complete lithium overlayer. The time-dependent thickness of the overlayer depends strongly on the mass and energy spectrum of the incident particle flux. It has been experimentally demonstrated that a significant fraction of the sputtered lithium is in the form Li+ and is returned to the surface by an electric field such as the sheath potential at the limiter, or a tangential magnetic field such as the toroidal field at the first wall; consequently, the overlayer lifetime is essentially unlimited.The TRIM computer code has been used to calculate the sputtering yield for pure metals and the partial sputtering yields of binary alloy components for various assumed solute concentration profiles. It is found that even with very low-Z coatings, the majority of the sputtered atoms originate in the uppermost atomic layer and that the partial sputtering yield of an alloy component is significantly reduced if that component is excluded from the uppermost atomic layer. It is predicted that the self-sputtering behavior of Cu-Li when used as a limiter or divertor plate will compare very favorably with that of tungsten.Calculations using the REDEP code bear out this expectation. At low plasma edge temperatures (< 50 eV), the net erosion (erosion minus redeposition) due to D,T,He and self-sputtering is nearly zero, while the gross erosion is less than that of Mo, For edge temperatures > 50 eV, W, and Mo are unusable due to self-sputtering. It is calculated that in the intermediate edge temperature regime (50–200 eV), a limiter made of copper with a lithium coating 1.5 monolayers thick would show net growth or erosion of < 3 mm per year. Consequently, Cu-Li alloy may be the only material suitable for use with intermediate plasma edge temperatures.

Effects of monolayer coverages on substrate sputtering yields

Abstract Materials currently being used or considered for plasma-side applications are not entirely satisfactory, particularly in the medium edge temperature (∼100–300 eV) regime. A new approach to impurity control based on self-sustaining surface segregated low-Z layers with high secondary ion fractions has been suggested and tested in laboratory experiments. A crucial requirement is that substrate sputtering yields be reduced about an order of magnitude by monolayer adsorbate coverages. Theoretical and experimental evidence is adduced to support the contention that overlayer coverages (a monolayer of Li on Cu) result in profound reductions of substrate (e.g., Cu) sputtering yields. The conclusion that a material such as a dilute alloy of Li in Cu could function as a limiter or a divertor plate material is, in part, based on the fact that more than 85% of the sputtered flux originates in the first atomic layer (e.g., Li) of the target.

Gibbsian and radiation-induced segregation in Cu–Li and Al–Li alloys

Previous experiments on segregation in dilute alloys of lithium in aluminum have demonstrated rapid enrichment of lithium in the uppermost monolayer, as well as a slower buildup in the subsurface region as a result of radiation-induced segregation effects during sputtering. Surface and subsurface enrichment of lithium in copper and aluminum alloys has been observed by secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES), and x-ray photoemission spectroscopy (XPS). The activation energies for lithium diffusion in Cu and Al have been measured and segregation kinetics are compared for dilute alloys of Li in Cu and Al, and a high lithium content copper alloy. The results are interpreted in terms of both Gibbsian and radiation-induced segregation effects.

On the spin-orbit scattering of conduction electrons in dilute non-magnetic alloys

Various predictions of a complete theory for spin flip scattering of conduction electrons in a binary alloys are discussed. It is shown that under certain approximations, the spin flip scattering produced by impurities in a metal is proportional to the difference in individual spin-orbit splittings of impurity and host. The theory is also shown to predict significant scattering due to the presence of spin-orbit holes. Satisfactory agreement is found with experiment for the scattering produced by Li in Cu and in Na and for Cu row impurities in Cu.