Liquid phase sintering and microstructure development of Ag-clad Tl-1223 superconductor

Temperature and time dependence of the phase formation in the (Cu0.5,Tl0.5)-1234 composition have been studied. The liquid–vapour deposition mechanism for the formation of 12(n − 1)n superconducting phases is presented. XRD, SEM, EDS and weight loss data are discussed. Samples were superconducting with maximum Tc and Jc (at 60 K and 0.5 T), determined from M(H) loops of 118 K and 4 × 105 A cm−2, respectively.

Section: Discussionmentioning

confidence: 99%

(Cu,Tl)Ba2Ca3Cu4Ox compositions: I. The influence of synthesis time and temperature on the phase formation and evaporation$ndash$condensation mechanism

Badica

Iyo

Crisan

et al. 2002

“…1234 phase. On the other hand, when oxygen pressure decreases the Tl-vapour pressure increases [9] and according to the same phase diagram [3] the equilibrium should shift in the opposite direction, i.e. to a 1223 phase formation.…”

Section: Tl and Oxygen Content In The Starting Composition Of The Sam...mentioning

confidence: 99%

“…From the different behaviour regarding J c in the two samples synthesized with the same heating rate (0.11 • C min −1 ), it seems that the final heat treatment temperature is important in order to enhance the critical current density. For a given oxygen partial pressure Hagen et al [9] showed that there is an optimum temperature for the synthesis of Tl-1223 tapes with maximum J c . However, the difference between the values of J c in our samples was relatively low.…”

Section: Heating Ratementioning

confidence: 99%

(Cu,Tl)Ba2Ca3Cu4Ox compositions: II. Heating rate applied to synthesis of superconducting ceramics

Badica

Iyo

Crisan

et al. 2002

Superconducting samples with a starting composition Cu0.5TlxBa2Ca3Cu4O12 (x = 1–0.35) were prepared in Au tubes from oxides by using different heating rates. The optimum heating rate was 0.11 °C min−1 applied between 860 and 880 °C. These samples show the highest content of 1234 phase and the lowest of Ba–Cu–O phases as well as the highest critical temperatures. The highest values were Tc = 119.2 K and Tc0 = 115.1 K. All samples show Jc values around 6 × 105 A cm−2, at 60 K and 0.5 T. In the rest of the samples, heated by using lower or higher heating rates, a high concentration of 1223 and/or 1245 phases is detected. The content of the 1234 phase and of Ba(Ca,Tl)–Cu–O residual liquid phase, in the samples synthesized for the optimum heating rate, depends on the Tl content in the starting mixture. The influence of the oxygen content in the starting mixture on phase composition is not as strong as of Tl, but it has a major role in establishing the superconducting behaviour of the 1234 grains. Some arguments that suggest the dependence of the transport properties of the non-superconducting matrix on oxygen content will be discussed. In our technological arrangement the determined optimum heating rate can be applied to the synthesis of other single-layered superconducting phases, e.g. 1212 phase from a Cu0.25Tl0.75Ba2CaCu2O8.115 starting composition.

“…Various phases of Tl-based superconductor can be prepared for both series. For high-current applications in strong magnetic fields, the single layer phase seems to have better advantage than the double layer phase [1,13,14]. In the single layer phases, the stronger coupling between conducting Cu-O planes separated by single-layer insulating Tl-O is responsible for the better J c property in higher magnetic fields [7,15].…”

Section: Introductionmentioning

confidence: 99%

“…In the single layer phases, the stronger coupling between conducting Cu-O planes separated by single-layer insulating Tl-O is responsible for the better J c property in higher magnetic fields [7,15]. Thus, single layer Tl-based phases such as the Tl-1223 and Tl-1212 are the better choice due to their reasonably high T c with excellent J c in the presence of magnetic fields [14][15][16][17][18][19]. The Tl-1212 phase is expected to preserve a higher fraction of its zero field J c values at higher fields due to stronger pinning between the Cu-O plane [20].…”

Section: Introductionmentioning

confidence: 99%

Transport critical current density of Ag-sheathed (Tl,Cr)Sr₂CaCu₂O₇high temperature superconductor tapes

A-Hamid

Abd‐Shukor

2001

Ag-sheathed Tl-1212 tapes with a nominal composition of (Tl1.2Cr0.15)Sr2CaCu2O7 were fabricated using the powder-in-tube (PIT) method. The tapes (~ 3-4 cm long) were annealed in oxygen flow at 820 °C, 870 °C and 890 °C each for 30 minutes, 1 hour and 5 hours, respectively. The x-ray diffraction (XRD) patterns for samples annealed at 820 °C and 870 °C showed the Tl-1212 as the dominant phase with Tl-1201 as minor phase. Scanning electron micrographs (SEM) revealed that the tapes showed no discernible favourable texture. Using a self-field approximation together with Jc dependence on temperature the characteristic length (Lc) associated with the pinning force is estimated to be approximately the same as the average grains size (Rg) for the tapes annealed at 820 °C for 30 minutes. For tapes that were annealed at 870 °C and 890 °C, Lc>Rg. The initial rapid suppression of Jc at low fields (<0.1 T) can be attributed to the weak-links phenomena as observed in other polycrystalline high-Tc materials with random grain orientations.