Magnitude Of Superconductivity Research Articles

Synthesis and Paraconductivity Studies of Fe–Pd Nanoparticles Added Cu0.5Tl0.5Ba2Ca3Cu4 O 12−δ Superconductors

Cu0.5Tl0.5Ba2Ca3Cu4O12−δ/(Fe–Pd 0, 0.5, 1.0, 1.5 %) superconductors are prepared at normal pressure by using three-step method. Alloy of Cu0.5Tl0.5Ba2Ca3 Cu4O12−δ/(Fe–Pd 1 %) have shown maximum increase in the magnitude of superconductivity. Cu 0.5Tl 0.5 Ba2Ca 3Cu 4O12−δ/(Fe–Pd 0, 0.5, 1.0, 1.5 %) samples have shown Tc(R= 0) around 106, 105.3, 102, and 100 K and the onset of diamagnetism around 113, 110, 102, and 105 K, respectively. A comparison of X-ray diffraction (XRD) scans of Fe–Pd nanoparticles with Cu0.5Tl0.5Ba2Ca3Cu4O12−δ/(Fe–Pd 0.5, 1.0, 1.5 %) superconducting samples have shown that the nanoparticles of Fe–Pd are quite stable in the matrix of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples even after repeated firing at 890 ∘C. With increase addition of Fe–Pd nanoparticles, the axes length increases, showing some inclusion of nanoparticle into the unit cell of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples from the termination ends of crystal.The inclusion of Fe–Pd in the superconducting Cu0.5Tl0.5Ba2Ca3Cu4O12−δ grains is also evidenced in Fourier transform infrared spectroscopy (FTIR) absorption measurements. The Fe–Pd nanoparticles added in Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples have been found to decrease the population of inter-grain voids that is found to increase the coherence length along the c-axis and the inter-layer coupling J. The FIC analysis of conductivity data haveshown the Fe–Pd nanoparticles diffusing into the inter-grain sites promoted an increase of penetration depth λp.d and Ginzburg–Landau parameter, κ. Due to the this possible diffusion of the Fe–Pd nanoparticles in the superconducting grains, the Tc(R= 0), Bc0(T), Bc1(T), and Jc(0) values are suppressed in Cu0.5Tl0.5Ba2Ca3Cu4O12−δ samples.

Superconductivity in transition metals.

A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified.

Significance of Phonon Modes and Excess Conductivity of (Cu0.5Tl0.5)Ba2Ca3(Cu4−x Ti x )O12−δ (x = 0, 0.25, 0.50, 0.75, 1.0) Superconductors

We have synthesized (Cu0.5Tl0.5)Ba2Ca3(Cu4−x Ti x )O12−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 CuO2/TiO2 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 arising from the decrease in the c-axes length. We attribute the suppression in B c, B c1, J c(0), and τ ϕ with Ti doping to the free energy difference between the normal and superconducting state. The idea of suppression in the density of phonon modes induced by Ti doping is supported by excess conductivity analyses.

Synthesis and excess conductivity analysis of TlBa2(Ca3−y Be y )Cu4O12−δ superconductors

TlBa2(Ca3−yBey)Cu4O12−δ (y = 0, 0.5, 1.0, 1.5, 2) samples are synthesized at normal pressure and the influence of doped Be-atoms on the superconductivity parameters at the microscopic level is investigated by carrying out excess conductivity analyses of conductivity data. The samples have shown tetragonal structure and the unit cell volume decreases with increased Be-doping. The onset temperature of superconductivity [Tc(onset)] and zero resistivity critical temperature [Tc(R = 0)] decrease with increased Be, however, the magnitude of diamagnetism is enhanced with Be (except for Be-doping of y = 1.0). The apical oxygen mode of the type Tl–OA–Cu(2) and CuO2 planar oxygen mode are softened as observed in FTIR absorption measurements. The FIC analyses of conductivity data have shown an increase in the coherence length along the c-axis and inter-plane coupling. The values of Bc0(T), Bc1(T), Jc(0), τφ are improved with the doping of Be. These observations suggested that due to the proximity effect there is less suppression in the value of the order parameter of the Cooper pairs from |ψ|2 = 1 value in the CuO2 planes in Be-doped samples that maintains the density of carriers in the conducting CuO2 planes [since the |ψ|2 = n/2] which promotes enhancement in the magnitude of superconductivity.

Mg-doped TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) superconductors

Ti-doped TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) samples are synthesized at 860 °C by two step solid state reaction method. All these samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity. The room temperature resistivity systematically increases with increased Mg contents in the final compound. The onset temperature of superconductivity [Tc(onset)], as observed in the resistivity and susceptibility measurements, and the zero resistivity critical temperature are found to increase for Mg-doping of x = 0.05 and 0.15; however, the values of these parameters are suppressed for Mg-doping of x = 0.25 and 0.35. Magnitude of the superconductivity also increases for Mg-doping of x = 0.05 and 0.15, whereas its values decrease for Mg-doping of x = 0.25 and 0.35. All TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) samples have shown orthorhombic crystal structure and the c-axis lattice parameter is systematically suppressed with the increase of Mg-doping. In the phonon modes assignment as observed from Fourier transform infrared spectrometer absorption measurements, the planar oxygen mode is softened, whereas the apical oxygen mode of type Tl-OA-Cu(2)/Ti is hardened with increased Mg-doping. The Oδ mode of oxygen atoms increases in intensity with increased Mg incorporation in the final compound. It is most likely that the density of phonon modes increases till mg-doping of x = 0.15, but for x = 0.25 and 0.35 the c-axis length decreases further, which may enhance the population of an-harmonic modes of oscillations. Such competitive modes of oscillations are most likely produced due to the presence of two different masses existing in the conducting CuO2/TiO2 planes, i.e., Ti (47.90 amu) and Cu (63.54 amu). Since the distance between the planes decreases with increased Mg-doping, the equilibrium population of the phonon modes in CuO2/TiO2 planes may also change and hence the Tc and magnitude of superconductivity. These observations strongly suggest the existence of electron-phonon interactions essential for the mechanism of high Tc superconductivity.

Ti-doped (Cu0.5Tl0.5)Ba2Ca2 (Cu3−xTix)O10−δ (x = 0, 0.25, 0.50, 0.75) superconductors

Ti-doped (Cu0.5Tl0.5)Ba2Ca2 (Cu3−xTix)O10−δ (x=0, 0.25, 0.50, 0.75) samples have been synthesized at 860°C by following two step solid state reaction methods and studied their superconducting properties by X-ray diffraction, resistivity, ac-susceptibility, FTIR absorption measurements. Ti-doped samples have shown orthorhombic crystal structure and the cell parameters increase with the increase of Ti-contents. The Tc(R=0) and onset of diamagnetism increases with increase Ti-doping in the final compound. The magnitude of superconductivity, however, increases for Ti-doping of y=0.25,0.75. The numbers of carriers in the conducting planes have been optimized by carrying out post-annealing of the samples in oxygen atmosphere. After the post-annealing the Tc(R=0) is improved in un-doped samples whereas it is suppressed in all Ti-doped samples. After post annealing in oxygen atmosphere, the magnitude of superconductivity (measured in emu/gm.Os) remains unchanged in un-doped samples whereas it is suppressed in all Ti-doped samples. In FTIR absorption measurements, the CuO2/TiO2 planar oxygen modes are slightly hardened in Ti-doped samples. The most likely reason for the hardening of the planar oxygen modes is decrease in the mass of Ti (47.90amu) in comparison with Cu (63.54amu) atoms; the atoms with lighter-mass vibrate at higher frequency. It is most likely that the existence of atoms of different masses in CuO2/TiO2 planes may suppress the density of phonon population due to setting-in of an-harmonic oscillations. The phonons of harmonic oscillation with wave vector q interact with q′ of an-harmonic oscillation and produce a new phonon with wave vector Q. The phonons with wave vector Q do not contribute in the Cooper-pair formation. It is most likely that a decrease in the population of desired phonons required for higher Tc occurs that in turn suppress the density of the Cooper-pair which in turn promote a decrease in the magnitude of superconductivity. These studies indicate the essential role of electron–phonons-interactions in the mechanism of high Tc superconductivity.

Enhancement in the Superconductivity of Tl(Ba2−x Mg x )(Ca1Be1)Cu3O10−δ System with the Decreased Thickness of Charge Reservoir Layer

Mg-doped Tl(Ba2−xMgx)(Ca1Be1)Cu3O10−δ (x=0, 0.25, 0.5, 0.75) superconductors are synthesized at the normal pressure and the possible mechanism of superconductivity in these compounds is studied. Tl(Ba2−xMgx)(Ca1Be1)Cu3O10−δ samples have shown an orthorhombic crystal structure and their c-axis length decreases with Mg doping. In these studies we have investigated the role of decreased thickness of charge reservoir layer in the mechanism of superconductivity. The Tc(R=0) in as-prepared Tl(Ba2−xMgx)(Ca1Be1)Cu3O10−δ (x=00, 0.25, 0.5, 0.75) samples was 97, 99, 100, 94 K and in oxygen post-annealed samples the Tc(R=0) is observed at 100, 98, 103, 101 K, respectively. The magnitude of the superconductivity after Mg doping is improved in Tl(Ba2−xMgx)(Ca1Be1)Cu3O10−δ (x=0, 0.25, 0.5, 0.75) samples. It was observed from the FTIR absorption measurements that the phonon modes related to CuO2 planar oxygen atoms are hardened with the doping of Mg in the charge reservoir layer. These studies have shown that the thickness of charge reservoir layer decreases with Mg doping which most likely makes charge transfer mechanism more efficient, promoting increase in the magnitude of superconductivity.

Enhancing Superconductivity in Low-dimensional TlBa2Ca2Cu3O10−δ System

Mg-doped Tl(Ba2−xMgx)Ca2Cu3O10−δ (x=0, 0.25, 0.50, 0.75, 1.0, 1.25, 1.5) superconductors are synthesized at the normal pressure and the possible mechanism of superconductivity in these compounds is studied. Tl(Ba2−xMgx)Ca2Cu3O10−δ samples have shown an orthorhombic crystal structure and their c-axis length decreases up to Mg-doping of x=0.75 and then increases up to Mg-doping of x=1.50. In these studies we have investigated the role of decreased thickness of charge reservoir layer on the mechanism of superconductivity. The Tc(R=0) in as-prepared Tl(Ba2−xMgx)Ca2Cu3O10−δ (x=0, 0.25, 0.5, 0.75, 1.0, 1.25) samples was 100, 98, 101, 102, 100, 96 K and in the oxygen post-annealed samples the Tc(R=0) is observed around 99, 98, 108, 127, 109, 97 K, respectively. The magnitude of the superconductivity after Mg-doping is improved in Tl(Ba2−xMgx)Ca2Cu3O10−δ (x=0.25, 0.5, 0.75, 1.0, 1.25) samples. It was observed from the FTIR absorption measurements that the phonon modes related to CuO2 planar oxygen atoms are hardened with the doping of Mg in the charge reservoir layer. These studies have shown that the thickness of charge reservoir layers decreases with Mg-doping, which most likely makes the charge transfer mechanism more efficient, which increases the magnitude of superconductivity in the final compound.

Enhanced Inter-grain Connectivity in Nano-particles Doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ Superconductors

Polycrystalline (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors show strong composition variations at the termination ends of the crystals which compromise over-all superconducting properties of the final compound. These composition variations are one of the root causes of void formation which produces a poor quality material. The better inter-grain coupling suppresses the Josephson losses required for higher transport critical current density (J c ). The lower losses across the inter-grain Josephson junctions are essential for wire and microelectronic applications. We have fixed such inadvertent composition variation in (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors by doping them with nano-particles of CuO, BaO and CaO2. Nano-particles doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors were synthesized at 860 °C and characterized using X-ray diffraction (XRD), resistivity (ρ), ac-susceptibility (χ), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) measurements. The magnitude of superconductivity is significantly enhanced with the doping of nano-particles. The samples with 15 wt. % addition of CuO nano-particles have even shown textured elongated crystalline with extremely low population of voids.

Cd-Doped Cu0.5Tl0.5Ba2Ca2Cu3−y Cd y O10−δ (y=0,0.5,1.0,1.5,2.0) Superconductors

Superconducting properties of cadmium doped Cu0.5Tl0.5Ba2Ca2Cu3−yCdyO10−δ (y=0,0.5,1.0,1.5,2.0) samples have been studied using X-ray diffraction, resistivity, ac-susceptibility and FTIR absorption measurements. In X-ray diffraction studies these samples have shown to have tetragonal structure. The zero resistivity critical temperature and magnitude of diamagnetism are suppressed with the increased incorporation of Cd in the final compound. A change in the shape of FTIR absorption spectra, after doping, has shown the incorporation of Cd in the unit cell. A systematic hardening of the apical oxygen modes and softening of the CuO2 planar modes of vibration with increased Cd doping have shown that it is incorporated in the unit cell of Cu0.5Tl0.5Ba2Ca2Cu3−yCdyO10−δ (y=0,0.5,1.0,1.5,2.0) superconductors. The FTIR absorption measurements of these samples have shown that hardening of the apical oxygen modes of types Cu(1)–O(2)–Tl and Cu(1)–O(2)–Cu(2)/Cdy (y=0,0.5,1.0,1.5,2.0) increases with the increase of Cd doping in the samples. A softening of the CuO2 planar oxygen mode Cu(2)–O–Cu(2) is also observed with the increased Cd doping in the final compound. It is most likely that hardening of the apical oxygen modes and the softening of the planar modes of vibration are associated damped harmonic oscillations produced by heavier Cd atoms in the CuO2 planes, which suppress the phonon population from a desired level, reducing the magnitude of superconductivity in the final compound.