Crystal structure of a new high-Tc TlBa2Ca3Cu4O11 superconductor by high-resolution electron microscopy.

Abstract

The crystal structure of a new high-${T}_{c}$ Tl${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$ ${\mathrm{O}}_{11}$ (1:2:3:4) superconductor was studied by a high-resolution electron microscopic measurement. The electron diffraction patterns give a simple tetragonal lattice with the lattice constants of $a=b=3.9$ \AA{} and $c=19$ \AA{}. The lattice image viewed along [010] showed clearly the single Tl-O layer alternating with four Cu-O sheets. The $A$-site layers of Ba or Ca atoms also alternate with the $B$-site layers of Tl or Cu atoms as in the layered perovskite compound ${\mathrm{ABO}}_{x}$. Since oxygen sites in the Ca layer are vacant, the structure is one of the oxygen-deficient perovskite. This phase has a new space group of $\frac{P4}{\mathrm{mmm}}$ different from the previous cuprate oxide superconductors and it has a large new superconductor family of $\mathrm{Tl}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{n\ensuremath{-}1}{\mathrm{Cu}}_{n}{\mathrm{O}}_{2n+3} (n=1,2,3,4,5,\dots{})$.