Synthesis, structure, and properties of ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{Cl}}_2$

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 °C in air and at 970 °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 Müller-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 ${\rho }_{\mathrm{ab}}$≃3000 Ω cm and ${\rho }_c$≃6.5×${10}^5$ Ω cm.