Properties and structures of R2-chiAchiCuO4 phases

The R2CuO4 phases for R = Pr and Nd were prepared and found to be semiconducting as previously reported. Crystal structures of both compounds were examined by a profile refinements of neutron powder diffraction data. A series of phases of the type R2-chiSrchiCuO4 which are isostructural with R2CuO4 for chi up to 0.1 were prepared and found to remain semiconducting. Chemical analysis indicates the presence of CuIII, yet these materials are not superconducting. This supports the view that R2CuO4 phases should be regarded as Mott insulators. A new series of phases possessing the tetragonal K2NiF4 structure appear in the Pr2-zSrchiCuO4 system for 1.0≤ chi ≤ 1.25. The new phases are semiconducting. The authors also find semiconductivity and not superconductivity for La2-chiAchiCuO4 where A is Pb or Cd. Reasons are discussed for why Ga, Sr, Ca and Na substitutions into La2CuO4 lead to superconductivity whereas the Pb and Cd substitutions do not