Although the prototype compound is a Mott Insulator (Li, 2022), (Ca,Sr)$_{3}$Cu$_{2}$O$_{4}$Cl$_{2}$ is an 80K superconductor.
Although (Huang, 1990) set the lattice constant $a$ = 3.861Å for Ca$_{3}$Cu$_{2}$O$_{4}$Cl$_{2}$, Table III of that paper suggests that the actual value is 3.8609Å.
$\frac{1}{2}a \,\mathbf{\hat{x}}- c z_{5} \,\mathbf{\hat{z}}$
(8g)
O I
References
J. Huang, R.-D. Hoffmann, and A. W. Sleight, New layered copper oxides containing double CuO$_{2}$ sheets: Ca$_{3}$Cu$_{2}$O$_{4}$Cl$_{2}$ and Ca$_{3}$Cu$_{2}$O$_{4}$Br$_{2}$, Mater. Res. Bull. 25, 1085–1090 (1990), doi:10.1016/0025-5408(90)90137-Q.
H. Li, S. Ye, J. Zhao, C. Jin, and Y. Wang, Temperature Dependence of the Electronic Structure of Ca$_{3}$Cu$_{2}$O$_{4}$Cl$_{2}$ Mott Insulator, Chinese Phys. Lett. 39, 017402 (2022), doi:10.1088/0256-307X/39/1/017402.
C.-Q. Jin, X.-J. Wu, P. Laffez, T. Tatsuki, T. Tamura, S. Adachi, H. Yamauchi, N. Koshizuka, and S. Tanaka, Superconductivity at 80 K in (Sr,Ca)$_{3}$Cu$_{2}$O$_{4 + \delta$}Cl$_{2-y}$ induced by apical oxygen doping, Nature 375, 301–303 (1995), doi:10.1038/375301a0.
Found in
\newcommand{\Ozolins}{Ozoli{ņ}{š}}\begin{thebibliography}{1}\expandafter\ifx\csname urlstyle\endcsname\relax \providecommand{\doi}[1]{doi:\discretionary{}{}{}#1}\else \providecommand{\doi}{doi:\discretionary{}{}{}\begingroup \urlstyle{rm}\Url}\fi\providecommand{\selectlanguage}[1]{\relax}\providecommand{\bibAnnoteFile}[1]{% \IfFileExists{#1}{\begin{quotation}\noindent\textsc{Key:} #1\ \textsc{Annotation:} \input{#1}\end{quotation}}{}}\providecommand{\bibAnnote}[2]{% \begin{quotation}\noindent\textsc{Key:} #1\ \textsc{Annotation:} #2\end{quotation}}\bibitem{symmetry/nCCOC/Ca3Cu2O4Cl2/Villars_Ca3Cu2O4Cl2_2011}P. Villars, K. Cenzual, J. Daams, R. Gladyshevskii, O. Shcherban, V. Dubenskyy, V. Kuprysyuk, I. Savysyuk, and R. Zaremba, Landolt-Börnstein - Group III Condensed Matter 43A10} (Springer, Berlin, Heidelberg, 2011), chap. Structure Types. Part 10: Space Groups (140)I4/mcm– (136)P4$_{2}$/mnm · Ca$_{3}$Cu$_{2}$O$_{4}$Cl$_{2}$, doi:10.1007/978-3-642-19662-1_238.\bibAnnoteFile{symmetry/nCCOC/Ca3Cu2O4Cl2/Villars_Ca3Cu2O4Cl2_2011
First cited in
N. Anderson, M. J. Mehl, H. Eckert, S. Divilov, X. Campilongo, S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 5. Submitted to Computational Materials Science (2026).