J.M. Liang

Superconductivity with Tc(zero) above 105 K in Tl-containing septenary oxides with Y1Ba2Cu3Oy-like structure

Abstract A family of high- T c superconductors with T c(zero) above 105 K is described. The compounds are seven-element blends with the general formula Tl 0.5 Pb 0.5 Ca 0.8 A 0.2 Sr 2 Cu 2 O x ( A = Y ), and rare-earth elements La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb). The results represent one of the first cases where chemical substitution has significantly raised T c in a known compound. The septenary compounds are tetragonal in structure with almost identical lattice parameters to those of now-famous Y 1 Ba 2 Cu 3 O y structure. The samples were highly reproducible, stable and remarkably homogeneous both in composition and structure. The preparative conditions were found to be much less stringent than those of other copper-based high- T c superconductors.

The fabrication and characterization of superconducting Tl-Pb-Ca-Pr-Sr-Cu-O compounds with Y1Ba2Cu3Oy-like structure and Tc (zero) up to 106 K

Bulk superconductivity with T c (zero) up to 106 K in a Tl 0.5 Pb 0.5 Ca 0.8 Pr 0.2 Sr 2 Cu 2 oxide with Y 1 Ba 2 Cu 3 O y -like structure was observed. A single phase, tetragonal structure with a = 0.382 ± 0.001 and c = 1.200 ± 0.001 nm and space group P4/mmm, was found in Tl 0.5 Pb 0.5 Ca 0.8 Pr 0.2 Sr 2 Cu 2 oxide samples by X-ray diffraction. T c (zero)s were found to be 78, 96, 106, 98, 45 and 25 K for Tl 0.5 Pb 0.5 Ca 1− x Pr x Sr 2 Cu 2 oxide samples with x = 0, 0.1, 0.2, 0.3, 0.5 and 0.7, respectively. For x = 1, the samples exhibited semiconducting behavior. All sintered samples were found to be remarkably homogeneous both in composition and structure. They were also exceptionally regular in microstructure and highly reproducible and stable. Although the six-metal blend makes the system appear to be rather complicated composition-wise, it is compensated by the relatively simple crystal structure. Furthermore, the preparation conditions are much less stringent than those for other copper-based high- T c superconductors.

Structural characterization of a TlCaBaCu oxide in Tc onset=155 K and Tc zero=123 K superconducting specimens

The crystal structure of a Tl‐Ca‐Ba‐Cu‐O compound in Tc onset=155 K and Tc zero=123 K superconducting specimens was characterized by transmission electron microscopy. Convergent beam electron diffraction analysis established that the phase is of P4/mcc space group. The lattice parameters of the phase were determined to be a=b=0.394 nm and c=3.95 nm. The phase was found to be primarily of a ten‐subcell structure by both high‐resolution lattice imaging and diffraction pattern analysis. The composition of the grains with the ten‐subcell structure being predominant was measured by energy dispersive spectrometry to be TlCa2Ba3Cu4Ox. Polytypes of the phase with four‐ and five‐subcell structures were also observed. The five‐subcell structure was identified to be of P4/mmm space group with a=b=0.394 nm and c=1.97 nm. The compositions of the specimens were measured to vary in composition ratios of Tl, Ca, Ba, and Cu from 1:2:2:3 to 1:2:3:4. The results strongly suggested that the TlCa2Ba3Cu4Ox phase is a high Tc s...

Synthesis and characterization for a new family of Tl-containing septenary oxides with Tc,zero above 105 K

Abstract Bulk superconductivity with Tc,zero above 105 K in Tl 0.5 Pb 0.5 (Ca 1−x A x )Sr 2 Cu 2 O y oxides (x=0.2, A=Y and rare-earth elements La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) with YBa 2 Cu 3 O y -like structure was observed. For A=Ce and mischmetal, Tc,zero was found to be 95 K and 101K with x=0.1. The results represent one of the few cases where chemical substitution has significantly raised Tc in a known compound. Single phase samples were prepared and were found to be highly reproducible and stable. Furthermore, the preparation conditions are much less stringent than those of other copper-based high-Tc superconductors.

Bulk superconductivity with Tc (zero) up to 95 K in a Tl0.5Pb0.5Ca0.9Ce0.1Sr2Cu2 oxide with an Y1Ba2Cu3Oy‐like structure

Bulk superconductivity with Tc (zero) up to 95 K in a Tl0.5Pb0.5Ca0.9Ce0.1Sr2Cu2 oxide with an Y1Ba2Cu3Oy ‐like structure was observed. Single‐phase samples, tetragonal in structure with a=0.380±0.001, c=1.195±0.001 nm, and of P4/mmm space group, were prepared. The results represent the first case where Ce substitution significantly raised the Tc of a known compound. The samples were remarkably homogeneous both in composition and structure. The compounds were highly reproducible and stable. The preparative conditions were found to be much less stringent than those of other copper‐based high Tc superconductors.

Epitaxial growth of high-Tc superconducting Tl-Ca-Ba-Cu-O films by liquid phase epataxial process

Abstract Tl-Ca-Ba-Cu-O epitaxial films have been successfully grown on (001) MgO substrate by liquid phase epitaxial (LPE) process. The as-grown films showed an onset of superconductivity at about 140 K and zero resistance at 111 K. X-ray diffraction analysis suggests the films to be highly preferentially oriented with the c -axis perpendicular to the film surface. Observation from transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed the presence of both Tl-Ca 2 Ba 2 Cu 3 O y and TlCa 2 Ba 3 Cu 4 O y phases.

Superconductivity of Y1Ba2−xSrxCu3Oy system

Tc depressed with increasing Sr substitution in YBa 2−x Sr x Cu 3 O y system. However x-ray diffraction revealed monophase similar to the basic 1-2-3 structure persists for X up to 1.0. Extensive dislocation was observed for X=1 which seems associated with local variation of Sr/Ba atomic ratio and arrangement.

Synthesis, transport, magnetization and structural characterizations of Tl-Ca-Ba-Cu-O specimens with T0=123 K and Tonset=155 K

Abstract A stable, reproducible and bulk superconductor of Tl-Ca-Ba-Cu-O (TCBCO) compound with T 0 above 120 K and T onset =155 K has been prepared. Measurements of electrical and magnetic properties are reported. On the basis of the transmission electron microscopy and X-ray diffraction analyses, the predominant phase was determined to be a body-centered tetragonal structure ( a = b =0.557 nm, c =3.77 nm) with a space group of I4/mcm. The composition ratios of Tl, Ca, Ba and Cu of the phase were determined by energy dispersive spectrometry to be 1:2:3:4. A probable structure model involving four layers of Cu-O interposed between Tl-O layers is proposed.

Structural and microstructural characterization of a high‐Tc superconducting YBaSrCu3O7−δ compound

Transmission electron microscopy (TEM), energy dispersive analysis of x ray (EDS), x‐ray diffraction, electrical resistance, and magnetic susceptibility measurements were applied to characterize the structure and microstructures of a high‐Tc superconducting YBaSrCu3O7−δ compound. The sintered samples were found to be predominantly of a single phase with a modified perovskite structure. Combined EDS/TEM and high‐resolution lattice imaging with computed image simulation data showed that the atomic ratio of Sr and Ba atoms is about unity and Ba sites in YBa2Cu3O7−δ compound were partially substituted by Sr atoms in the three‐layer perovskite structure, in agreement with the results of a previous neutron diffraction study. It was also found that the marked contrast difference in high‐resolution images along [100] and [010] directions of the high‐Tc oxygen‐deficient superconducting crystals can be used to advantage to distinguish [100] and [010] directions of the modified perovskite structure in TEM. Lattice d...

Structural and microstructural characterization of a high-T/sub c/ superconducting YBaSrCu/sub 3/O/sub 7-//sub delta/ compound

Transmission electron microscopy (TEM), energy dispersive analysis of x ray (EDS), x‐ray diffraction, electrical resistance, and magnetic susceptibility measurements were applied to characterize the structure and microstructures of a high‐Tc superconducting YBaSrCu3O7−δ compound. The sintered samples were found to be predominantly of a single phase with a modified perovskite structure. Combined EDS/TEM and high‐resolution lattice imaging with computed image simulation data showed that the atomic ratio of Sr and Ba atoms is about unity and Ba sites in YBa2Cu3O7−δ compound were partially substituted by Sr atoms in the three‐layer perovskite structure, in agreement with the results of a previous neutron diffraction study. It was also found that the marked contrast difference in high‐resolution images along [100] and [010] directions of the high‐Tc oxygen‐deficient superconducting crystals can be used to advantage to distinguish [100] and [010] directions of the modified perovskite structure in TEM. Lattice d...