Uniformly layered mixtures of the Bi2Sr2Can−1CunOn+4 phases formed in artificially layered films—structural analysis and superconducting properties

Abstract

Uniformly layered mixtures of the succeeding members of Bi2Sr2Can−1 CunO2n+4 series were found in the films synthesized by alternating sputter deposition of BiO, SrCu0.5O1.5, and CaCuO2 layers. The uniformly layered intergrowth was caused by the deviation of the CaCuO2 supply amount in each sequence, which is constant throughout the synthesis, from the stoichiometric amount. It is presented that the x-ray diffraction peaks from the films with uniform intergrowth can be indexed by treating them as the satellites of superlattices. In this treatment, the number of CuO2 layers, which varies randomly but uniformly along the c axis, is expressed on average by noninteger n. The superconducting transition temperature (Tc) and concentration of holes in the CuO2 layers in those films decreased with increasing n (2.88≤n≤6) monotonically. From the continuity of the decrease in Tc with n, we conclude that the hole concentration is averaged between the two phases in the intergrowth by the diffusion of the holes.