Crystal structure of (Cu,C)Ba2Ca3Cu4O11+ delta (Tc=117 K) by neutron-powder-diffraction analysis.

Abstract

The crystal structure of the newly discovered 117-K superconductor, (Cu,C)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{11+\mathrm{\ensuremath{\delta}}}$, has been refined from time-of-flight neutron-powder-diffraction data. The structure has ``average'' tetragonal symmetry and is similar to that of Tl(or Hg)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{\mathit{y}}$. C atoms in ${\mathrm{CO}}_{3}$ groups substitute at the Cu site in the (Cu,C)${\mathrm{O}}_{1+\mathrm{\ensuremath{\delta}}}$ layer leading to a chemical composition of (${\mathrm{Cu}}_{0.68}$${\mathrm{C}}_{0.32}$)${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{11.06}$. This compound has two inequivalent kinds of ${\mathrm{CuO}}_{2}$ layers with pyramidal and square coordination of Cu to oxygen. The inner ${\mathrm{CuO}}_{2}$ layers with Cu in four coordination are less corrugated than the outer ones with Cu in five coordination, and exhibit a structure very similar to those of infinite-layer compounds.