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

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Abstract
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 superconducting phase with an exciting possibility that superconducting transition occurs at 155 K for this phase.

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