Superconductivity in (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu3−ySiyO10−δ samples (original) (raw)
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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.
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
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.
Superconductivity in Co doped Cu 0.5Tl 0.5Ba 2(CaM)Cu 2.95Co 0.05O 10− δ (M = Mg, Be) samples
Journal of Alloys and Compounds, 2009
We have investigated the possible source of suppression of superconductivity in Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 2.95 Co 0.05 O 10−ı samples. We substituted Mg (r = 0.65 Å) and Be (r = 0.31 Å) at Ca (r = 0.99 Å) sites in Cu 0.5 Tl 0.5 Ba 2 CaMCu 2.95 Co 0.05 O 10−ı (M = Mg, Be) superconductor to enhance interplanar coupling and Li in the charge reservoir layer (Cu 0.5 Tl 0.25 Li 0.25 )Ba 2 O 4−ı 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 0.5 Tl 0.5 Ba 2 CaMCu 2.95 Co 0.05 O 10−ı 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 0.5 Tl 0.5 Ba 2 CaMCu 2.95 Co 0.05 O 10−ı (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 0.5 Tl 0.5 Ba 2 O 4−ı charge reservoir layer supplies the required number of carriers to the CuO 2 planes; therefore, the critical temperature is increased in Li doped samples.
Journal of Alloys and Compounds, 2009
The effects of Fe-doping on superconductivity and structure of Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3−y Fe y O 10−ı (y = 0, 0.02, 0.03, 0.05, 0.075) superconductors are investigated by means of resistivity, AC-susceptibility measurements, X-ray diffraction (XRD) and thermogravimetric analysis. The X-ray data indicates that the lattice parameters a and c vary but structure of the samples remain tetragonal with predominant CuTl-1223 phase. The c-axis length observed by X-ray diffraction analysis has been found to decrease with the increased Fe-doping content in the unit cell. The thermogravimetric analysis shows that Fe 3+ ions replacing for Cu 2+ ions can bring excess oxygen atoms into lattice and form some Fe O defect clusters. In the doping level of Fe (y = 0-0.075), both zero-resistance temperature T c (R = 0) and the magnitude of diamagnetic signal decrease linearly with the increasing amount of Fe. The striking linear depression of T (R = 0) and the magnitude of diamagnetism suggest the potential effects of charge localization on the transport properties and also shows that Fe dopants occupy different Cu sites in a stable manner with Fe content increasing. The post-annealing experiments demonstrated that the magnitude of diamagnetism as well as T c (R = 0) is enhanced. It may be due to the delocalization of carriers which result into the enhancement of the density of mobile carriers in the conducting CuO 2 planes. Our discussion suggests that the micro structural distortion and the excess oxygen defect induced by Fe-doping encourage in the localization of mobile carriers in conducting CuO 2 planes, which is one of the reasons to explain the decrease of T c (R = 0) and carrier concentration.
A study of superconducting (Y1−xCax)Ba2Cu3Oy
Physics Letters A, 1997
We have investiga~d the effects of hole doping in the Y-Ba-Cu-0 system by substituting calcium(r~~ in the YfIB)-site. We have analysed the resistivity, pa~conductivity, interlayer coupling strength (J) as a function of dopant concentration. T, and J are found to decrease with increasing calcium content. We have also studied surface binding energies of various components in a Ca doped sample through secondary ion mass spectrometry (SIMS). The binding energy of CuO in a CuO, sheet does not increase as compared to that in undoped YBCO, indicating that the extra hole doped in the Y site does not bring positive charge to the conducting CuO, layer. Doping of calcium perhaps destroys the ordering of oxygen in the Cu-0-Cu chain, which affects su~rconductivity.
2018
Ti-doped (Cu 0.5 Tl 0.5)Ba 2 (Ca 2−x Ti x)Cu 3 O 10−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconductors have been synthesized by solid state reaction method. The prepared samples are characterized by XRD, electrical resistivity, AC susceptibility and FTIR techniques. XRD analysis showed that the lattice parameters are marginally altered but there is no substantial change with the doping of Ti. All the samples are found with orthorhombic crystal structure following PMMM space group. T c (R = 0) is enhanced with the doping of Ti except for x = 1.0 sample. The magnitude of diamagnetism in the AC-susceptibility measurements is enhanced up to x = 0.5 and decreased beyond. The FTIR measurements show that the apical oxygen phonon modes are softened. The planar oxygen phonon modes are softened but their intensity is raised with the enhanced Ti contents. This softening of the planar oxygen phonon modes may be arising due to the heavier Ti ions (47.9 amu) at the lighter Ca (40.07 amu) sites. Variation in the lattice parameters in the XRD data and shifting of various oxygen phonon modes in the FTIR data show that Ti is incorporated at Ca sites in the unit cell. Increase in the superconducting properties up to certain doping level (x = 0.75) may be arising due to the improved interplane coupling caused by the smaller sized Ti at Ca sites. While the decrease in T c and magnitude of diamagnetism beyond x = 0.75 and x = 0.5 respectively, is attributed to the suppressed density of a particular type of phonons required for optimum superconductivity. This suppression in the density of the desired phonons is brought about by the substitution of heavier Ti ions at the lighter Ca sites. This study signifies the role of electron-phonon interaction in mechanism of high T c superconductivity.