Synthesis, structure, and properties ofSr2CuO2

Syntheses of single-crystal specimens and single-phase polycrystalline samples of ${\mathrm{Sr}}_{2}$${\mathrm{CuO}}_{2}$${\mathrm{Cl}}_{2}$ are reported. Differential-thermal-analysis measurements indicate that this compound melts incongruently at 990 \ifmmode^\circ\else\textdegree\fi{}C in air and at 970 \ifmmode^\circ\else\textdegree\fi{}C in helium. Rietveld refinement of powder neutron diffraction data confirms the body-centered-tetragonal (I4/mmm) ${\mathrm{K}}_{2}$${\mathrm{NiF}}_{4}$-type structure found earlier using x-ray techniques by Grande and M\"uller-Buschbaum. The ${\mathrm{CuO}}_{2}$ planes are the same as in (tetragonal) ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, but the out-of-${\mathrm{CuO}}_{2}$-plane oxygens in the latter are replaced by Cl. The temperature dependences of the lattice parameters and thermal factors are reported; the tetragonal structure is retained from 300 K down to at least 25 K. Electrical-resistivity measurements exhibit essentially insulating behavior near room temperature, with ${\ensuremath{\rho}}_{\mathrm{ab}}$\ensuremath{\simeq}3000 \ensuremath{\Omega} cm and ${\ensuremath{\rho}}_{c}$\ensuremath{\simeq}6.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ \ensuremath{\Omega} cm.