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

Abstract

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.

Thermal expansion measurements of (Cu0.25Tl0.75)-1234 added by MgO-nano particles

“…Very small amounts of impurities such as (Cu, Tl)-1223 and Ba 2 Cu 3 O 6 appear in the diffraction patterns. These impurities were also observed by Badica et al [4] in (Cu, Tl)-1234 phase, prepared using solid-state reaction technique. The volume fractions of these phases can be estimated using various methods [11,12].…”

“…3(a-d), respectively. More grains with regular plate-like or bar-like can be observed in x = 0.0, 0.2 wt.% and 0.6 wt.%, indicating the formation of (Cu, Tl)-1234 phase [4]. Some blocks of several composed plates or bars were also observed, especially in x = 0.6.…”

“…(3) 18.822 (7) 3.813 (5) 18.802 (7) 160 3.838 (1) 18.679(0) 3.818 (8) 18.759(0) 3.803 (7) 18.818 (8) 3.811 (9) 18.798 (8) 120 3.837 (9) 18.678 (9) 3.816 (4) 18.752 (4) 3.801 (3) 18.812 (2) 3.809 (5) 18.792 (2) 80 3.836 (7) 18.678 (8) 3.816 (4) 18.734 (6) 3.801 (3) 18.794 (4) 3.809 (5) 18.774 (4) the lowest porosity. A small curvature above the superconducting transition temperature T c is observed, for all the samples, which is a characteristic of superconducting thermodynamic fluctuations [17].…”

“…Khan et al [2] reported a simple and direct method for (Cu 1−x Tl x )-1234 synthesis at normal pressure based on solid-state reaction technique using Ba(NO 3 ) 2 , CaCO 3 , Cu(CN) and Tl 2 O 3 . A single phase of (Cu 1−x Tl x )-1234 was achieved with T c around 120 K and zero resistivity temperature T c0 at about 106 K. Badica et al [4] prepared Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 O 12−ı starting from the oxide elements at different heating rates in Au-tubes. The samples' optimum heating rate was found to be 0.1 • C/min when sintered between 860 • C and 880 • C. The highest obtained values of T c and T c0 were 119.2 K and 115.1 K, respectively.…”

Ion Beam Analysis and Electrical Resistivity Studies of (Cu0.5Tl0.5)-1223 Phase with Added Nano-oxides

“…It is clear that the samples morphology consists of randomly oriented plate-like grains, indicating the phase formation of (Cu 0.5 Tl 0.5 )-1223. Badica et al [37] found that grains with plate-like morphology was an advanced stage of (Cu Tl)-Ba 2 Ca 3 Cu 4 O z phase. Also, it is clear for all the samples that there is a little number of irregular shaped and spherical grains embedded between the plate-like grains of (Cu 0.5 Tl 0.5 )-1223 phase.…”