New La₂CuO₄ derivatives La_2-2xSr_2xCu_1-xM_xO₄(M=Ti,Mn,Fe,or Ru): a study of linear Cu-O-M electronic interaction in two dimensions

Abstract

Oxides of the general formula La_2-2xSr_2xCu^II_1-xM^IV_x O₄(M=Ti, Mn, Fe, or Ru), crystallizing in the tetragonal K₂NiF₄structure, have been synthesized. For M=Ti, only the x=0.5 member could be prepared, while for M=Mn and Fe, the composition range is 0<x<1.0, and for M=Ru, the composition range is 0<x≤0.5. There is no evidence for an ordering of Cu(II) and M(IV) in the x=0.5 members. While the members of the M=Ti, Mn, and Ru series are semiconducting/insulating, the members of the M=Fe series are metallic, showing a broad metal-semiconductor transition around 100 K for 0<x≤0.15 that is possibly related to a Cu(II)-O-Fe(IV)↔Cu(III)O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La_2-2xSr_2xCu_1-xFe_xO₄ for x≤0.20 renders the samples metallic but not superconducting.