C. Y. Shei

Formation mechanism study of REBa2Cu4O8+δ (RE=Y and Dy) accelerated by nitric acid

An accelerated formation of REBa2Cu4O8+δ (RE=Y and Dy) was observed as a suitable amount of nitric acid was added. This provides an excellent route for preparing high‐ purity REBa2Cu4O8+δ in ∼ 30 h. X‐ray diffraction and thermal analyses (TGA/DTA) were conducted to reveal the formation mechanism. The addition of nitric acid did not change the reaction routes but formed more Ba2Cu3O5 which might play an important role for the formation of REBa2Cu4O8+δ. Magnetization data confirmed the Tc’s of 80 and 75 K for as‐prepared Y‐124 and Dy‐124, respectively.

Preparation of high-purity Tl-based 1223'' superconductor phase by modified Pechini process in water solution

Because of the mixed metal valance state of thallium in a Tl‐based superconductor, a nearly single ‘‘1223’’ phase can be readily prepared by a modified Pechini method (US Patent 3 330 697). Tl2O3 and other metal nitrates are dissolved in an aqueous solution plus a certain amount of oxalic acid for chelating the metal cations. The desired phase shows zero resistance at 114 K and the phase purity is identified by x‐ray diffraction. Characteristics of superconductivity also are evidenced by the Meissner effect. The preparation technique is considered valuable to purify multiphase superconductors for mass production.

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF (TL0.5PB0.5)SR2(CA1-XTHX)CU2OY SYSTEM FOR X = 0.0 - 0.3

Abstract To reveal the correlation between the Tc temperatures and the hole concentration in p-type cuprates superconductors, a series of samples of (Tl0.5Pb0.5)Sr2(Ca1-xThx)Cu2Oy (x = 0.0 − 0.3) were prepared and investigated by the X-ray photoelectron spectroscopy. The core-level of Cu did not show consistent variation while a slight shifting of Tl 4f 7 2 , 5 2 peaked up to high binding energy as Th dopant increased. This might be resulted from the decrease of the hole concentration in Tl-O layer. The Sr core-level spectra demonstrated an evident and consistent variation which could be attributed to two lattice sites available for Sr atoms and the decrease of Ca atoms. Our results indicated that the Tl-O layer might act as “hole reservoir”, which had been already suggested by the band structure calculation.

Formation of (Tl, Pb, Bi)Sr1.6Ca2.4Cu3Oy superconducting phase with Tc = 105 K by nitrates conversion

Abstract In the study of (Tl, Pb, Bi)-Sr-Ca-Cu-O systemm, a nitrate conversion method was developed to prepare (Tl, Pb, Bi)Sr1.6Ca2.4Cu3Oy (1223 phase) with high yield in short reaction time. Also, the well mixing of precursors including Tl2O3 could be achieved avoiding a two-stage reaction. The studies of individual reactant indicated that all the reactants were nitrates except the formation of thallium oxide. Moreover, a quick oxidation from Tl+ to Tl3+ was speculated after carrying out a titrametric method. X-ray diffraction investigation as well as physical characterizations confirmed the formation of 1223 phase from as-prepared precursors. This method provides a possible and simple route to make the 1223 sample in large scale.

Th doping effect of the (Tl0.5Pb0.5)Sr2(Ca1-xThx)Cu2Oy (1212) phase

The series of high Tc superconductors (Tl0.5Pb0.5)Sr2(Ca1−xThx)Cu2Oy (x = 0.0 – 0.3), with highest Tc ∼ 88K for (Tl0.5Pb0.5)Sr2(Ca0.9Th0.1)Cu2Oy, were prepared by two steps solid state reaction. XRD and high-resolution transmission electron microscope imaging study indicated that it crystallized in the TlSr2CaCu2Oy-type tetragonal structure with unit cell lattice parameters a = 3.810(1)r and c = 12.105(5)r. EDS analyses on single grains of x = 0.1 sample showed the incorporation of Th into the sample. Both resistivity and magnetization measurements revealed that the Tc was 10K higher than that of (Tl0.5Pb0.5)Sr2CaCu2Oy. This enhanced Tc might be due to the decrease of the hole concentration of the compound.