Domains and Na substitution in the superconductor Y_0.6Na_0.4Ba₂Cu_2.7Zn_0.3O_7–δ

Abstract

The high-temperature superconductor Y_0.6Na_0.4Ba₂Cu_2.7Zn_0.3O_{7– δ} , with a T _c of about 60 K, has been studied by electron diffraction and high-resolution electron microscopy. High densities of twin boundaries and anti-phase boundaries are observed and analysed. Darkness-level profiles at the positions of Ba and Y atoms in the [100] experimental and simulated images are used to determine the position and content of the Na atoms. It is shown that Na substitutes for Y in the crystal structure and the atomic ratio between Na and Y can be estimated quasi-quantitatively.

Acknowledgements

The authors thank Professor R. Wang for reading the paper and offering valuable comments. Y. M. Wang thanks Dr Y. Yao for helpful discussions. This project is supported by the National Natural Science Foundation of China (Grant-10474122).