Frequency dependent dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor ARTICLE in JOURNAL OF APPLIED PHYSICS · JANUARY 2012 Fluctuation induced conductivity in " Cu 0.5 Tl 0.5−x K x …Ba 2 Ca 3 Cu 4 O 12− superconductor (original) (raw)
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Frequency dependent dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor
Journal of Applied Physics, 2012
The fluctuation induced conductivity ͑FIC͒ of ͑Cu 0.5 Tl 0.5−x K x ͒Ba 2 Ca 3 Cu 4 O 12−y ͑x=0,0.25͒ superconductor has been studied after potassium substitution at thallium site in the charge reservoir layer ͑Cu 0.5 Tl 0.5 Ba 2 O 4−y ͒. The samples were also post-annealed in oxygen to change the carrier density in CuO 2 planes. The zero resistivity critical temperature T c ͑0͒ was found to increase after K +1 substitution at Tl +3 sites in the Cu 0.5 Tl 0.5 Ba 2 O 4−y charge reservoir layer. However, T c ͑0͒ has been suppressed after post-annealing the samples in oxygen. The FIC analysis was performed in the frame work of Aslamasov-Larkin theory. The results of FIC analysis have shown three-dimensional ͑3D͒, two dimensional ͑2D͒ and short wavelength fluctuations ͑SWFs͒ in the order parameter. It has been also observed that there is an increase in the 3D-2D and 2D-SWF cross-over temperatures after potassium substitution along with an increase in T c ͑0͒. However, after post-annealing in oxygen, the dimensional cross-over has been shifted to lower temperatures. A direct correlation between the cross-over temperatures, the T c ͑0͒ as well as carrier doping level has been observed.
Journal of Low Temperature Physics, 2012
The fluctuation induced conductivity ͑FIC͒ of ͑Cu 0.5 Tl 0.5−x K x ͒Ba 2 Ca 3 Cu 4 O 12−y ͑x=0,0.25͒ superconductor has been studied after potassium substitution at thallium site in the charge reservoir layer ͑Cu 0.5 Tl 0.5 Ba 2 O 4−y ͒. The samples were also post-annealed in oxygen to change the carrier density in CuO 2 planes. The zero resistivity critical temperature T c ͑0͒ was found to increase after K +1 substitution at Tl +3 sites in the Cu 0.5 Tl 0.5 Ba 2 O 4−y charge reservoir layer. However, T c ͑0͒ has been suppressed after post-annealing the samples in oxygen. The FIC analysis was performed in the frame work of Aslamasov-Larkin theory. The results of FIC analysis have shown three-dimensional ͑3D͒, two dimensional ͑2D͒ and short wavelength fluctuations ͑SWFs͒ in the order parameter. It has been also observed that there is an increase in the 3D-2D and 2D-SWF cross-over temperatures after potassium substitution along with an increase in T c ͑0͒. However, after post-annealing in oxygen, the dimensional cross-over has been shifted to lower temperatures. A direct correlation between the cross-over temperatures, the T c ͑0͒ as well as carrier doping level has been observed.
Fluctuation induced conductivity in (Cu0.5Tl0.5−xKx)Ba2Ca3Cu4O12−δ superconductor
Journal of Applied Physics, 2011
The fluctuation induced conductivity ͑FIC͒ of ͑Cu 0.5 Tl 0.5−x K x ͒Ba 2 Ca 3 Cu 4 O 12−y ͑x=0,0.25͒ superconductor has been studied after potassium substitution at thallium site in the charge reservoir layer ͑Cu 0.5 Tl 0.5 Ba 2 O 4−y ͒. The samples were also post-annealed in oxygen to change the carrier density in CuO 2 planes. The zero resistivity critical temperature T c ͑0͒ was found to increase after K +1 substitution at Tl +3 sites in the Cu 0.5 Tl 0.5 Ba 2 O 4−y charge reservoir layer. However, T c ͑0͒ has been suppressed after post-annealing the samples in oxygen. The FIC analysis was performed in the frame work of Aslamasov-Larkin theory. The results of FIC analysis have shown three-dimensional ͑3D͒, two dimensional ͑2D͒ and short wavelength fluctuations ͑SWFs͒ in the order parameter. It has been also observed that there is an increase in the 3D-2D and 2D-SWF cross-over temperatures after potassium substitution along with an increase in T c ͑0͒. However, after post-annealing in oxygen, the dimensional cross-over has been shifted to lower temperatures. A direct correlation between the cross-over temperatures, the T c ͑0͒ as well as carrier doping level has been observed.
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.
Journal of Superconductivity and Novel Magnetism, 2015
We have synthesized (Cu 0.5 Tl 0.5)Ba 2 Ca 3 (Cu 4−x Ti x)O 12−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconductors by two-step solid-state reaction method at 880 • C. The a-axis length of tetragonal unit cell increases, whereas the c-axis decreases with doping of Ti in the final compound revealed by X-ray diffraction measurements. Moreover, the magnitude of superconductivity suppresses with increased Ti doping. The Fourier transform infrared spectrometer (FTIR) absorption measurements have shown that the peak position of the apical oxygen modes at 480 and 540 cm −1 remains unchanged, whereas the CuO 2 /TiO 2 planar oxygen modes is softened with increased Ti doping. We explained the softening of planar oxygen mode to be arising due to the difference in the atomic masses of Ti (47.90 amu) and Cu (63.54 amu) atoms. The suppression of superconductivity magnitude is suggested to be originating from an-harmonic oscillations induced by doped Ti atoms which in turn suppress the density of phonon population. These studies show the importance of density of phonon population in mechanism of high-T c superconductivity and hence the electron-phonon interactions. The excess conductivity analyses (FIC) of conductivity data of these samples have shown that with increased Ti doping, the mean field critical temperature T cmf is shifted to lower temperatures. The increase in the coherence length along the c-axis, interlayer coupling, and the Fermi velocity is suggested to be
Ceramics International, 2014
Be-doped TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ (y ¼ 0, 0.25, 0.5, 0.75, and 1.0) superconductor bulk samples were synthesized by solid state reaction and characterized by X-ray diffraction (XRD), dc-resistivity {ρ (Ω cm)}, and Fourier Transform Infrared (FTIR) absorption spectroscopy. Fluctuations induced conductivity (FIC) analysis is carried out on temperature dependent dc-resistivity data of as-prepared and oxygen postannealed TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ superconductor samples by using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models for excess conductivity. Different microscopic parameters such as zero temperature coherence length along c-axis {ξ c (0)}, inter-layer coupling (J), intergrain coupling (α), critical exponent (λ D ) and dimensionality of fluctuations are calculated for understanding the role of Be-doping on superconducting properties of TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ samples. The cross-over temperature (T o ) is shifted towards higher temperature values with the increase of Be contents in TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ samples. The increase in ξ c (0) and J after Be-doping at Ca sites shows the improvement of inter-plane coupling in TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ samples. The increase in zero resistivity critical temperature {T c(R ¼ 0) (K)} up to y ¼0.5 and then decrease for y ¼ 0.75, 1.00 fixed the Be-doping level for optimum increase of superconducting properties of TlBa 2 (Ca 2 À y Be y )Cu 3 O 10 À δ samples. The appreciable changes in all the microscopic parameters extracted from the FIC analysis and the increase in relative intensity of almost all the oxygen phonon modes indicate the oxygen diffusion in the unit cell after oxygen post-annealing the samples. The oxygen diffusion can take place at both inter-granular and intra-granular sites, which increase the superconducting volume fraction by improving the grains size, inter-grain connectivity and carrier density.
Physica B-condensed Matter, 2010
Fluctuation induced conductivity of Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 À y Sn y O 10 À d superconductors have been studied from the resistivity vs. temperature data. The logarithmic plots of excess conductivity (Ds) vs. reduced temperatures ½e ¼ ðTÀT mf c Þ=T mf c show two crossover temperatures with three exponents. A distinct cross-over from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov-Larkin equations have been observed in all the samples. Another cross over from 2D to 0D fluctuations has also been witnessed. The FIC data fits well with 3D, 2D and 0D fluctuations for lower Sn doping, while it deviates considerably for higher Sn concentration. Also the FIC analysis shows the deterioration in quality of samples (increased DT c), increase in anisotropy and decrease in inter-layer coupling strength J with increased Sn content. These factors might be contributing to the suppression of T c in these samples.
Journal of Applied Physics, 2012
The effect of oxygen annealing on the excess conductivity of Cu 0.5 Tl 0.25 M 0.25 Ba 2 Ca 2 Cu 3 O 10Àd (M ¼ K, Na, Li, Tl) samples is investigated. From the analysis of results, we have evaluated the exponents, the coherence length, the crossover temperature, and interlayer coupling strength (J) of the samples. These studies show that the K-doped post-annealed sample has shown narrow transition width with improvement in 2D and 3D conductivities. Oxygen annealing has also enhanced the coherence length and interlayer coupling strength of the material. Na-and Li-doped postannealed samples have shown increased transition width, poor 2D and 3D conductivities within narrow temperature windows. After annealing, reduction in coherence length and the interlayer coupling strength is also observed. While in Tl-doped sample, oxygen annealing has not caused much deviation in fluctuation induced conductivity (FIC) parameters. The underlying cause of improved behavior of post-annealed K-doped sample is also discussed.
Dielectric properties of oxygen post-annealed Cu0.5Tl0.5Ba2Ca3(Cu4−yCdy)O12−δ bulk superconductor
Ceramics International, 2013
Oxygen post-annealing experiments are carried out to optimize the oxygen contents in Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4−y Cd y)O 12−δ (y ¼ 0, 0.25, 0.5, and 0.75) superconductor samples and to investigate its effects on their dielectric properties {i.e. dielectric constants (ε′ r , ε″ r), absolute dielectric loss | tan δ| and ac-conductivity (s ac)}. The negative capacitance (NC) is observed in all post-annealed Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4−y Cd y)O 12−δ samples. Almost all the dielectric properties are suppressed except dielectric loss (tan δ), which is increased after oxygen post-annealing. The appreciable change in the dielectric properties is the indication of oxygen intake by Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4−y Cd y)O 12−δ samples after oxygen post-annealing. The thermal agitation is higher and polarizability is lower at normal state (300 K), resulting in decrease of the dielectric constant and increase in tan δ which is vice versa at lower temperatures. The observed variation in the dielectric behavior of Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4−y Cd y)O 12−δ samples strongly depends on the working (or operating) temperature and frequency of the external applied ac-field. The dielectric behavior of the material can be regulated by the post-annealing in oxygen as a result of which the variation of oxygen content of the materials structures may take place thus changing the carrier's density. On the other hand, this post-annealing may affect the inter-grain connectivity of the materials that can influence the dielectric properties of the material.