Physical Properties of A₂Cu₃O₄X₂(A=Alkali-Earth Elements;X=Halogen) with the Cu₃O₄Plane

Abstract

First, we have studied the stability of Sr_2-xBa_xCu₃O₄Cl_2-yBr_y of the 2342 phase with the Cu₃O₄ plane, which is composed of the Cu(1)O₂ and extra Cu(2) sublattices, in the temperature range between 600 and 950°C. It has been found that a mixture of (Sr, Ba)₂CuO₂(Cl, Br)₂ With the CuO₂ plane and CuO becomes stable instead of the 2342 phase with the Cu₃O₄ plane for smaller values of x and y at low temperatures. Next, the electrical and magnetic properties of Sr_2-xBa_xCu₃O₄Cl_2-yBr_y with the Cu₃O₄ plane have been investigated. The electrical resistivity exhibits semiconductive behavior. The magnetic susceptibility shows three-dimensional antiferromagnetic order below T_N(1)=300-400K and T_N(2)-30K for the Cu(1) and Cu(2) sublattices, respectively. A broad peak due to the two-dimensional antiferromagnetic order in the Cu(2) sublattice is also observed around T_N^2D(2)=100K. With increasing x and y, the lattice parameters increase, the electrical resistivity increases and values of both T_N(1) and T_N ^2D(2) decrease. These results are explained as being due to the decrease of the overlaps between Cu3d and O2p, COP, Br4p orbits.