Comparison of carrier concentration determined by structural and electrical studies of cation substituted YSr2Cu3O7−δ (original) (raw)
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Physica C: Superconductivity, 2005
We report systematic studies of structural, microstructural and transport properties of Y 1-x Ca x Ba 2 Cu 3 O 7-δ bulk samples with 0.20 ≥ x ≥ 0.0. The partial substitution of Ca 2+ at Y 3+ site in YBa 2 Cu 3 O 7-δ leads towards slightly overdoped regime, which along with disorder in CuO 2 planes is responsible for decrease in superconducting transition temperature (T c ) of the doped system. The microstructural variants being studied by transmission electron microscopy (TEM) technique in imaging and selected area diffraction modes revealed an increase in the density of twins with increase in Ca concentration despite the fact that there is slight decrease in the orthorhombicity. This is against the general conviction of decrease in twin density with decreasing orthorhombicity. An increase in twin density results in sharpening of twin boundaries with increasing Ca concentration. These sharpened twin boundaries may work as effective pinning centers. A possible correlation between microstructural features and superconducting properties has been put forward and discussed in the present investigation.
Effect of Co-Ga paired substitution on superconductivity in YBa2Cu3O7-d
2004
The effect of Co-Ga paired substitution on the superconducting properties of YBa 2 Cu 3 O 7-δ (Y-123) has been investigated by X-ray diffraction, ac susceptibility, dc resistivity and oxygen content measurements. We report in this paper the results of our studies on the paired substitution of a magnetic and non-magnetic ion at Cu site in Y-123, while keeping the total dopant concentration fixed. The simultaneous substitution of Co and Ga at Cu site shows variation in the transition temperature (T c ), oxygen content and hole concentration as a function of change in the balance of magnetic (Co) and nonmagnetic (Ga) concentration. Orthorhombicity (D), given as (b-a)/a, also varies as a function of increasing dopant concentration. The variation in T c due to Co-Ga substitution is discussed in the light of dopant valency and hole filling mechanism. KEYWORDS A. Oxides, A. Magnetic materials D. Superconductivity
Journal of Solid State Chemistry, 2004
The effect of Sr II -for-Ba II isovalent substitution on the magnetic irreversibility field (H irr ) of Cu(Ba 1-y Sr y ) 2 YbCu 2 O 6.95(2) (Cu-1212) sample series (y = 0 ∼ 0.4) is studied to reveal guiding rules for tailoring the intrinsic H irr characteristics of high-T c superconductors. It has been assumed that substitution of the larger alkaline earth cation, Ba II , by the smaller, Sr II , might improve the H irr characteristics as a consequence of the decrease in the thickness of nonsuperconductive blocking block (BB). However, results of the present work show that Sr substitution rather depresses the H irr characteristics of the Cu -1212-phase superconductors even though the thickness of BB decreases. Both the amount of excess oxygen and the overall positive charge are confirmed to remain constant upon the Sr substitution by wet-chemical and XANES analyses, respectively. However, from neutron diffraction data analysis it is found that Sr substitution breaks the conductive CuO chains in BB by shifting part of the excess oxygen atoms from the characteristic b-axis lattice site to the a-axis site. This is believed to decrease the concentration of mobile holes in the BB, as supported by the results of TEP measurements. The lower H irr (T) lines of the Srsubstituted samples may thus be attributed to the lower concentration of mobile holes in BB.
Effect of Co-Ga Paired Substitution on Superconductivity in YBa2Cu3O7-delta
Modern Physics Letters B, 2004
The effect of Co-Ga paired substitution on the superconducting properties of YBa2Cu3O7-δ (Y-123) has been investigated by X-ray diffraction, ac susceptibility, dc resistivity and oxygen content measurements. We report in this paper the results of our studies on the paired substitution of a magnetic and non-magnetic ion at Cu site in Y-123, while keeping the total dopant concentration fixed. The simultaneous substitution of Co and Ga at Cu site shows variation in the transition temperature (Tc), oxygen content and hole concentration as a function of change in the balance of magnetic (Co) and non-magnetic (Ga) concentration. Orthorhombicity (D), given as (b-a)/a, also varies as a function of increasing dopant concentration. The variation in Tc due to Co-Ga substitution is discussed in the light of dopant valency and hole filling mechanism.
Effect of Sc and Ti doping on superconducting and magnetic properties in DyBa2Cu3O7−z
Journal of Magnetism and Magnetic Materials, 2004
The effects of Sc and Ti substitutions on magnetic and superconducting properties of DyBa 2 ðCu 1Àx M x Þ 3 O 7Àz ; (M ¼ Sc or Ti, x ¼ 0:00; 0:03; 0:05; 0:10) system have been investigated. Decrease of T c with increasing Sc or Ti dopings in the system is observed, which is attributed to hole-filling mechanism. The paramagnetic moment ðB10:4 m B =f:u:Þ from Curie-Weiss fit is found to be slightly less than the paramagnetic moment of free Dy 3þ ion. The observed dopant concentration dependent upward curvatures in magnetization in diamagnetic region are discussed in the light of various possibilities. r
Cu NMR and NQR study of impurity-doped YBa2Cu3O7
Physica B: Condensed Matter, 1993
The superconducting property in impurity-doped YBaz(Cu~ xMx)307 (M = Zn and Ni) has been investigated by measuring the nuclear spin-lattice relaxation time T~ and the Knight shift of 63Cu in the CuO 2 plane. We have found that Zn doping into the CuO 2 plane in YBa2Cu307 causes gapless superconductivity at low T, giving rise to a finite density of states at the Fermi surface, while magnetic Ni doping into the CuO 2 plane reduces T~ moderately, although Ni spins behave as local moments. The gapless feature in Zn-doped YBCO 7 can be consistently interpreted in the framework of the d-wave model with gap zeros of lines at the Fermi surface, as argued for heavy-fermion superconductors.
Microstructural and Superconducting Properties of YBa2Cu3-xCoxO7-δ System
Integrated Ferroelectrics, 2011
Bulk superconductor samples of YBa2Cu3-xCoxO7-δ with x = 0, 0.01, 0.03, 0.05 are synthesized by solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification, intergrowths, dislocations and the local structure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure/phase of YBa2Cu3-xCoxO7-δ do not change with the substitution of Co up to x = 0.05. The zero resistance critical transition temperature [Tc(R = 0)] is found to decrease and critical current density (Jc) increases with the increased concentration of cobalt in the compound. The Jc enhancement for the cobalt doped samples may be resulting due to flux pinning from some defects such as planar defects, stacking faults and micro defects (twin, domains etc.) and the rapid suppression in Tc may be due to the cooper pair breaking and the hole filling in the CuO2 planes.
Physical Review B, 2004
Knight shift, spin-echo dephasing, and spin-lattice relaxation measurements have been carried out in Y 1Ϫx Ca x Ba 2 Cu 3 O y. Underdoped and overdoped samples have been obtained by means of Y 3ϩ for Ca 2ϩ substitutions in the parent chain-empty antiferromagnetic ͑AF͒ YBa 2 Cu 3 O 6.1 and in the chain-full YBa 2 Cu 3 O 7 , respectively. Unexpected effects, as the divergence of relaxation rate with the concurrent broadening of the NMR line in the underdoped superconducting phase and the inadequacy of the Korringa relation between the relaxation rate 1/T 1 and Knight shift, even in the overdoped regime, suggest that a revision of the commonly accepted view of YBa 2 Cu 3 O 6ϩy compounds is required. In particular the linear temperature dependence of T 1 Ϫ1 and the temperature behavior of Knight shift cannot be accounted for over all the temperature range. In the underdoped superconducting phase the divergence of 1/T 1 on cooling is associated with the slowing down of excitations possibly related to sliding motions of orbital currents, or with the concurrent freezing of AF correlated spins. Echo-dephasing measurements evidence an extreme slowing down of longitudinal spin fluctuations which appear to be driven by a different dynamic, related either to flux line motions or to 63,65 Cu spin-lattice relaxation.
Journal of Applied Physics, 2005
Results of phase formation, resistivity (ρ), and thermo-electric power (S), are reported on Y 1-x Ca x Ba 2 Cu 2.7 Co 0.3 O 7 compounds with x = 0.1 and 0.2. Pristine compound i.e. without Co or Ca substitution crystallizes in orthorhombic structure with space group P/mmm. Cu-site Co substituted compound i.e. YBa 2 Cu 2.7 Co 0.3 O 7 is tetragonal. With simultaneous doping of Ca at Y site in Co substituted compound i.e. Y 1-x Ca x Ba 2 Cu 2.7 Co 0.3 O 7 the tetragonal nature still remains. ρ(T) measurements showed superconducting transition temperature (T c) to decrease from 90K (YBa 2 Cu 3 O 7) to 33 K for YBa 2 Cu 2.7 Co 0.3 O 7 which with further Ca substitution increases from 33K to 53K (Y 0.9 Ca 0.1 Ba 2 Cu 2.7 Co 0.3 O 7) and 67 K for Y 0.8 Ca 0.2 Ba 2 Cu 2.7 Co 0.3 O 7. T c decreases first with Cu-site Co substitution by hole-filling and later recovers by simultaneous hole creation by Y site Ca substitution. Room temperature thermoelectric power S(300 K), which is an indirect measure of mobile carriers shows the decrease of carriers with Co doping and creation by Ca substitution. Our results demonstrate the hole filling by Co substitution is compensated by simultaneous Ca substitution.
Investigation of physical and structural properties of cs doped y1ba2cu3o7 superconductors
Cumhuriyet Science Journal, 2021
In this work, YBa2‑xCsxCu3O7‑δ (x= 0.05, 0.1, 0.2 and 0.3 wt. %) samples were prepared by using solid state reaction method. Some electrical, physical and structural properties of these compounds were examined by using SEM (scanning electron microscopy), XRD (X-ray diffraction), electrical resistivity, critical current density and AC susceptibility measurements, respectively. On the basis of the SEM measurements, it would seem that increasing the amount of Cs doping, the porous structures decrease and the grain size increases up to approximately 50 μm. Unit cell parameters were calculated by employing XRD measurements. On the basis of the data obtained from X-ray diffraction, Cs atoms displaced Ba atoms in the crystal structure. From the measurements of electrical resistivity at 80 K-120 K temperature, it was determined that the highest transition temperature was 91.5 K after addition of 0.05 wt. % Cs. The critical transition temperature was decreased by increasing the amount of Cs ...