Homogeneous distribution of carriers in the conducting planes by Zn substitution at Cu sites in Cu0.5Tl0.5Ba2Ca3Cu4O12−δ superconductors (original) (raw)
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Excess conductivity of Cu0.5Tl0.5Ba2Ca3Cu4−yZnyO12−δ superconductors
Low Temperature Physics, 2012
Oxide high-T c superconductors (HTSC) are anisotropic in character since the charge carriers have free moment in the conducting CuO 2 planes [1] whereas their motion is impeded by insulating/partially insulating MBa 2 O 4-δ (M = Y, Bi, Hg, Tl, CuTl, etc.) charge reservoir layers. In the transport process the charge carriers have to tunnel across insulating/partially insulating barriers along the c-axis and across the grain boundaries, which promote a fluctuation in the order parameter and in turn to the conductivity of the carriers. The studies of such fluctuation conductivity (FIC) may help in understanding the intrinsic mechanism of superconductivity. Here the electrical resistivity ρ(T) versus temperature data of as-prepared and oxygen post-annealed Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4-y Zn y O 12-δ (y = 0, 0.5, 1.5, 2.5) samples is studied for FIC analyses in the temperature regime well above the critical temperature; such analyses have been carried out by employing Lawrence and Doniach (LD) and Maki-Thompson (MT) models. The coherence length, inter-plane coupling, exponent, dimensionality of fluctuations and the phase relaxation time of the carriers are determined from such analyses. It is observed that the crossover temperature associated with two distinct exponents fits very well with the two-dimensional (2D) and three-dimensional (3D) LD equations. The crossover temperature T 0 is shifted to higher temperatures with enhanced Zn doping. The 3D LD region is shifted to higher temperature with the increased Zn doping. We have elucidated from these analyses that lower Tl content in the final compound may increase the charge carrier's doping efficiency of MBa 2 O 4-δ charge reservoir layer, resulting into an increase in the coherence length along the c-axis and superconductivity parameters. A small decrease in the coherence length along the c-axis ξ c (0) is observed in the samples with Zn doping of y = 1.5 whereas ξ c (0) increases in the samples y = 0.5, 2.5. In comparison with as-prepared samples, the ξ c (0) decreases after post-annealing in oxygen atmosphere. It is most likely that a decrease in the density of charge carrier's is promoted by oxygen diffusion in the unit cell may suppress the ξ c (0). The increase oxygen diffusion is evidenced from the softening of phonon modes after postannealing in oxygen atmosphere. The decreased population of small spins of Cu atoms induced by doping of Zn is viewed in the terms of suppression of spin gap and hence the pseudo-gap in Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4-y Zn y O 12-δ (y = 0, 0.5, 1.5, 2.5) samples.
Cu0.5Tl0.5Ba2Ca3Cu4−y Zn y O12−δ (y=0, 1.0, 2.0, 3.0, 3.5): Superconductor with Four ZnO2 Planes
Journal of Low Temperature Physics, 2007
A new Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4−y Zn y O 12−δ (y = 0, 1.0, 2.0, 3.0, 3.5) superconductor with four ZnO 2 planes is reported. The structure of the material remains tetragonal for all Zn doping concentration. The substitution of Zn at CuO 2 planar site was carried out following Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4−y Zn y O 12−δ (y = 0, 1.0, 2.0, 3.0, 3.5) formula. Contrary to all previous studies of Zn doping in all copper oxide high temperature superconductors, the zero resistivity critical temperature T c (R = 0), critical current density and quantity of diamagnetism increase with increased Zn concentration. The onset temperature of superconductivity in these samples was observed at 128 K and T c (R = 0) at 122 K for y = 3.5. The volume of the unit cell observed through X-ray diffraction scan is found to decrease with increase Zn doping; promoting an increase in Fermi vector K F and effective density of states which results in enhanced superconductivity parameters. The synthesis of Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4−y Zn y O 12−δ material by this method is highly reproducible.
Enhanced Superconductivity in�(Cu0.5Tl0.25Cs0.25)Ba2Ca2Cu3O10-d by Cs Doping
J Low Temp Phys, 2008
The self doping of carriers in CuO 2 planes (accomplished through post annealing in air, N 2 and O 2 atmospheres in previous studies) is replaced by a more efficient alkali metal dopant such as Cs. The doping of Cs in the Cu 0.5 Tl 0.5 Ba 2 O 4−δ charge reservoir of Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 O 10−δ superconductors has been found to enhance its superconducting properties. Enhanced superconductivity parameters, such as T c , H c and J c , most likely arise from the enhanced doping efficiency of Cu 0.5 Tl 0.25 Cs 0.25 Ba 2 O 4−δ charge reservoir layer; since the alkali metals are known to lose their outermost "s-orbital" electron, which could be supplied to conducting CuO 2 planes. The distance between efficiently doped CuO 2 planes is reduced by Be and Mg doping at the Ca Sites. The quantity of diamagnetism and zero resistivity critical temperature [T c (R = 0)] are suppressed by these substitutions. The postannealing of the Cs doped samples further enhances their superconducting properties; oxygen doping most likely promotes the optimum holes concentration in the superconducting state in the Cs doped samples. These observations have also shown that the free carrier density plays a significant role in the mechanism of superconductivity which was accomplished by synthesizing (Cu 0.5 Tl 0.25 Cs 0.25 )Ba 2 Ca 2 Cu 3 O 10−δ superconductors.
Enhanced Superconductivity in (Cu0.5Tl0.25Cs0.25)Ba2Ca2Cu3O10−δ by Cs Doping
Journal of Low Temperature Physics, 2008
The self doping of carriers in CuO 2 planes (accomplished through post annealing in air, N 2 and O 2 atmospheres in previous studies) is replaced by a more efficient alkali metal dopant such as Cs. The doping of Cs in the Cu 0.5 Tl 0.5 Ba 2 O 4−δ charge reservoir of Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 O 10−δ superconductors has been found to enhance its superconducting properties. Enhanced superconductivity parameters, such as T c , H c and J c , most likely arise from the enhanced doping efficiency of Cu 0.5 Tl 0.25 Cs 0.25 Ba 2 O 4−δ charge reservoir layer; since the alkali metals are known to lose their outermost "s-orbital" electron, which could be supplied to conducting CuO 2 planes. The distance between efficiently doped CuO 2 planes is reduced by Be and Mg doping at the Ca Sites. The quantity of diamagnetism and zero resistivity critical temperature [T c (R = 0)] are suppressed by these substitutions. The postannealing of the Cs doped samples further enhances their superconducting properties; oxygen doping most likely promotes the optimum holes concentration in the superconducting state in the Cs doped samples. These observations have also shown that the free carrier density plays a significant role in the mechanism of superconductivity which was accomplished by synthesizing (Cu 0.5 Tl 0.25 Cs 0.25)Ba 2 Ca 2 Cu 3 O 10−δ superconductors. Keywords (Cu 0.5 Tl 0.25 Cs 0.25)Ba 2 Ca 2 Cu 3 O 10−δ superconductors • Higher T c (R = 0) with Cs doping • Enhanced diamagnetism • Post-annealing
Doping of the CuO2 planes of Cu1−xTlxBa2Ca2Cu3O10−y superconductor via light and heavier ions
Physica C: Superconductivity, 2003
The superconducting properties of Cu 1Àx Tl x Ba 2 Ca 2 Cu 3 O 10Ày thin films prepared by amorphous phase epitaxial (APE) method have been studied, by resistivity measurements, X-ray diffraction, electron microscopy and infrared spectroscopy. The main emphasis of this research work is on the doping of the charge reservoir layer, which ultimately controls carrier concentration in the CuO 2 conducting planes. The phenomena of the superconductivity, takes place in the conducting CuO 2 planes, however, we can control it via charge concentration in the CuO 2 planes. We have done this by carrying out annealing experiments in different conditions i.e. in air, nitrogen atmosphere and in vacuum. In these annealing experiments the doping is carried out by intercalation of the light O 2 in the CuO chains and by the removal of heavy thallium from the CuO chain axis. The removal of thallium at 717°C from the CuO chains shifted the T c (R ¼ 0) to higher values and the doping of oxygen and nitrogen at 450°C increased the semiconductivity and shifted the T c (onset) to lower values. The removal of oxygen from CuO chains by vacuum annealing at 450°C has also increased the degree of semiconductivity and shifted the T c (onset) to lower temperatures. The XRD of the samples of Cu 1Àx Tl x -1223 phase showed the predominant c-axis oriented material with c-axis lattice constant 15.53 A A. The electron micrograph of these samples showed elongated grains with the grains ends fused together. The surface roughness of the samples was below 0.2 lm. The infrared absorption measurements have shown the softening of 451 cm À1 mode after removal of oxygen from the unit cell, which shows that oxygen doping controls the carrier concentration in the charge reservoir layer and hence the superconductivity in the material.
2014
O 10-d samples are synthesized by a solid-state reaction method and characterized by X-ray diffraction, DC resistivity (q), AC susceptibility (v ac ) and Fourier transform infrared absorption spectroscopy. The suppression of zero resistivity critical temperature (T c (R = 0)) and the magnitude of diamagnetism is most likely due to the reduced efficiency with which (Tl 1-x Y x )Ba 2 O 4-d charge reservoir layer supplies the carriers to the CuO 2 planes. The localization at Y 3+ reduces the number of carriers in the CuO 2 planes and thereby promotes antiferromagnetism, which is fatal for superconductivity.
Physica C: Superconductivity, 2009
Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors Fourier transforms infrared absorption spectroscopy (FTIR) X-ray diffraction (XRD) Annealing a b s t r a c t In order to study the higher carrier's doping efficiency of (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer to the conducting CuO 2 planes we have incorporated Bi in (Cu 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu 0.25 Tl 0.5 Bi 0.25)Ba 2 Ca 2 Cu 3 O 10Àd , (Bi 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd , (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2 Cu 3 O 10Àd and (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2Ày Be y Cu 3 O 10Àd superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO 2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO 2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer promotes an increase in the c-axis length which in turn increase the anisotropy and decrease the Fermi-vector [k F = (3p 2 N/V) 1/3 ] and Fermi-velocity ½v F ¼ ðpe c D= hÞ of the carriers. We have decreased the c-axis length of Bi doped compounds by doping Be at the Ca sites in (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2-Ca 2Ày Be y Cu 3 O 10Àd superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of T c (R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance k F , v F and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO 2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.
Superconductivity in (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu3−ySiyO10−δ samples
Solid State Sciences, 2010
The (Cu 0.5 Tl 0.25 Li 0.25)Ba 2 Ca 2 Cu 3Ày Si y O 10Àd (y ¼ 0, 0.25 0.5, 0.75, 1.0, 1.25) superconductor samples have been prepared by solid-state reaction method. The critical temperature and as well as the magnitude of diamagnetism is increased up to Si concentration y ¼ 1.0, however, from the doping level y ¼ 1.25 a decrease in the critical temperature along with the vanishing of the diamagnetism was observed. The carrier's in the conducting CuO 2 /SiO 2 planes were optimized by carrying out post-annealing in oxygen and an increase in the critical temperature was observed in all Si doped samples. The doping efficiency of Cu 0.5 Tl 0.5 Ba 2 O 4Àd charge reservoir layer in (Cu 0.5 Tl 0.25 Li 0.25)Ba 2 Ca 2 Cu 3Ày Si y O 10Àd (y ¼ 0, 0.25 0.5, 0.75, 1.0, 1.25) samples is enhanced by doping Li þ1 ion; as alkali metals are known to easily loose their outer most electron which could be supplied to CuO 2 /SiO 2 conducting planes and would suppress the anti-ferromagnetism in the inner conducting planes. The FTIR absorption measurements have provided an indirect evidence of Si substitution at in CuO 2 planes.