T c increase with Ag addition in the 596-1596-1596-1system
01 Jun 1988-Journal of Materials Science Letters (Kluwer Academic Publishers)-Vol. 7, Iss: 6, pp 596-598
About: This article is published in Journal of Materials Science Letters.The article was published on 1988-06-01. It has received 23 citations till now. The article focuses on the topics: Critical point (thermodynamics) & Inorganic compound.
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TL;DR: In this paper, the effects of Ag and Ag2 O additions on the mechanical and superconducting properties of YBa2 Cu3 O7−δ superconductors were studied.
Abstract: The effects of Ag and Ag2 O additions on the mechanical and superconducting properties of YBa2 Cu3 O7−δ superconductors were studied. The addition of 20‐vol % Ag resulted in an increase in strength from ≊40 to 75 MPa and a twofold increase in the critical current density (Jc ) of YBa2 Cu3 O7−δ bar specimens. These improvements are believed to be due to the increased density. Furthermore, Ag particles may relax the residual stresses resulting from the expansion anisotropy of individual grains, and may provide increased resistance to crack propagation by pinning the propagating cracks; these effects would also increase the strength. The addition of 30‐vol % Ag resulted in an increase in strength to 87 MPa, but it was associated with a decrease in Jc . This decrease in Jc at high Ag content is believed to be due to the presence of oxygen deficient nonsuperconducting tetragonal phase as well as continuous Ag phase. Similar effects were also observed after Ag2 O additions.
179 citations
TL;DR: A review of the literature on substitutions and their effect on the properties of the 90 K superconductor YBa 2 Cu 3 O δ (YBCO) can be found in this paper.
Abstract: The 90 K superconductor, YBa 2 Cu 3 O δ (YBCO), has proved to be highly adaptable chemically as it can accommodate a wide variety of cationic and anionic substitutions. Indeed, the majority of the chemical elements, excluding noble gases and actinides, have been reported to substitute to some extent into the YBCO structure. This review covers the literature on such substitutions and their effect on the properties of YBCO. Reported solubility limits are given, together with crystal symmetry and trends in unit cell parameters with dopant concentration. The dopant site is considered; this is additionally complex in the case of copper substitution because of the two distinct copper sites in the crystal structure. The effect of the dopant on the critical temperature, T c , is reviewed; the literature is often contradictory due to the dual effects of variable oxygen content and the nature of the dopant. Preparation methods appear to have an effect on solubility limits, crystal symmetry and T c , Also, the methods used to determine solubility limits are often imprecise which can lead to contradictions. The magnetic properties of doped materials are reviewed; for some dopants, particularly the magnetic lanthanides, antiferromagnetism and superconductivity co-exist. The related RBa 2 Cu 3 O δ phases (R = lanthanide), their structure, properties and behaviour on doping are reviewed in a similar way. For the larger rare earths, the related systems R 1+ x Ba 2- x CU 3 O δ , are reviewed; as x increases, the transition temperature decreases and compositions R 1.5 Ba 1.5 Cu 3 O δ are semiconducting. The upper and lower solubility limit changes with R, and for R = Dy, the upper limit is x = 0 composition, LaBa 2 Cu 3 O δ , cannot be prepared in air since substitution of La onto the Ba site occurs, forming the Ba-deficient solid solutions. The discovery of superconductivity above liquid nitrogen temperatures in YBa 2 Cu 3 O 7 , has generated a vast quantity of research; to date, > 20 000 papers have appeared on the 123 materials (source: BIDS). This review, therefore, cannot be comprehensive, but attempts to highlight important substitutions, their effect on the properties of YBCO and any contradictions in the literature.
100 citations
TL;DR: In this article, the origin of silver doping effects on Y•Ba•Cu•O superconducting ceramics, such as a high temperature shift of the point at zero resistivity in resistivity measurements and an increase in critical current density, was sought by transmission electron microscopy observations.
Abstract: The origin of silver doping effects on Y‐Ba‐Cu‐O superconducting ceramics, such as a high‐temperature shift of the point at zero resistivity in resistivity measurements and an increase in critical current density, was sought by transmission electron microscopy observations. Sintering was strongly promoted together with suppression of the formation of the liquid phase in the grain boundaries by silver. Consequently, the liquid phase, which is not a superconductor, was not present in almost all the grain boundaries of the silver‐doped ceramics, while this phase was present in almost all the grain boundaries in pure ceramics.
50 citations
TL;DR: In this article, the effect of silver solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ (0≤x≤0.5) superconductors has been evaluated.
Abstract: The effect of silver (Ag) solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ (0≤x≤0.5) superconductors has been evaluated. The solubility limit of Ag for copper sites in YBCO at ambient conditions (room temperature, atmospheric pressure) was evaluated to be x≂0.06. Analysis revealed the Ag content (x) of YBCO grains to be lower than the nominal Ag content (xn) used for fabrication, probably due to processing‐related problems. Part of the Ag used for fabrication segregates on the YBCO grain boundaries. The segregated Ag particles are believed to pin YBCO grains, resulting in fine‐grain microstructures. For low nominal Ag content, xn<0.2, critical current density (Jc) increased from 98 to 160 A/cm2 as a function of increasing Ag content. These improvements are believed to be due to the increased oxygen content and associated microstructural changes in the YBCO. For higher nominal Ag content, xn≳0.2, however, Jc decreased rapidly with the increasing Ag content due to the precipit...
46 citations
TL;DR: In this paper, the effect of silver (Ag) addition on the resistance to thermal shock and delayed failure of YBa2Cu3O7−δ superconducting wires has been evaluated.
Abstract: The effect of silver (Ag) addition on the resistance to thermal shock and delayed failure of YBa2Cu3O7−δ superconducting wires has been evaluated. Resistance to thermal shock was evaluated by measuring the critical-current density (Jc) as a function of the number of thermal cycles for YBCO and its composites with 15 vol. % Ag additions. Composite YBCO-Ag wires show a slower decrease in Jc than does monolithic YBCO as the number of thermal cycles increases. The nature of delayed failure was studied by measuring strength (σf) as a function of loading rate (
$\dot \sigma $
) and evaluating the value of the subcritical crack growth parameter N[σf = A
$\dot \sigma $
1/(N+1)]. The value of the N parameter was observed to increase slightly from 35 for YBCO to 41 for YBCO-Ag composites. The improved resistance to thermal shock and subcritical crack growth is believed to be due to improvements in mechanical properties (strength and fracture toughness) and thermal conductivity of YBCO as a result of Ag addition.
34 citations
References
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TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: Structural, magnetic and electronic properties of compounds in the series RBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ (R = Nd,Sm,..., and Lu) were studied and it was shown that changes in oxygen content in these materials drastically affect their physical properties.
Abstract: Structural, magnetic and electronic properties of compounds in the series R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ (R=Nd,Sm,..., and Lu) were studied. Resistivity, Meissner-effect, and shielding measurements have revealed superconductivity among all the rare-earth compounds, except La, Pr, and Tb, with critical temperatures ${T}_{c}$ measured at the midpoint of the resistive transition ranging from 87 to 95 K. No depression of ${T}_{c}$ was observed upon introduction of most of the rare-earth magnetic ions. Susceptibility measurements down to 1.6 K have shown that an antiferromagnetic ordering (most likely due to dipole-dipole interactions) occurs only for the Gd compound. Changes in oxygen content in these materials drastically affect their physical properties. The importance of the cooling rate during the synthesis of the sample has been correlated to oxygen content. ${T}_{c}$'s are optimized by slow cooling. Annealing at 700\ifmmode^\circ\else\textdegree\fi{}C in oxygen pressure of 40 atmospheres slightly increase ${T}_{c}$, while annealing under vacuum at 420\ifmmode^\circ\else\textdegree\fi{}C destroys ${T}_{c}$ and induces a semiconducting behavior. These changes in oxygen content and ${T}_{c}$ are perfectly reversible.
522 citations
TL;DR: The phase responsible for superconductivity above 90 K in the Y-Ba-Cu-O system has been tentatively identified as the La/sub 3-//sub x/Ba/sub 6/O/sub 14+//sub y/-type structure through a combination of x-ray diffraction and superconducting transport measurements.
Abstract: The phase responsible for superconductivity above 90 K in the Y-Ba-Cu-O system has been tentatively identified as the La/sub 3-//sub x/Ba/sub 3+//sub x/Cu/sub 6/O/sub 14+//sub y/-type structure through a combination of x-ray diffraction and superconducting transport measurements.
59 citations
TL;DR: In this article, the electron-electron scattering in the alkali metals has been calculated using first-principles pseudopotentials, including Coulomb scattering and phonon-exchange scattering.
Abstract: The umklapp fraction, $\ensuremath{\Delta}$, for electron-electron scattering in the alkali metals has been calculated using first-principles pseudopotentials. Both Coulomb scattering and phonon-exchange scattering have been included. For a given pseudopotential and a given approximation to the effective electron-electron interaction, our results for the Coulomb scattering contribution to $\ensuremath{\Delta}$ are up to a factor of \ensuremath{\sim}100 smaller than those of an earlier calculation. The sources of this discrepancy have been analyzed. On the basis of these calculations we suggest that the scattering amplitude for umklapp electron-electron scattering in the alkali metals is dominated by the phonon-exchange contribution. The improved treatment of the Coulomb contribution to the scattering amplitude and the inclusion of the phonon-exchange contribution combine to yield a coefficient of ${T}^{2}$ in the low-$T$ electrical resistivity which is larger than earlier theoretical values for Li and Na, about the same size for K, and smaller for Rb and Cs.
48 citations
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46 citations