Brief overview of research on Na_xCoO_2 system and iron-based superconductor In this chapter,the author has reviewed the basic physical properties and some hot topics in Na_xCoO_2 system and iron-based superconductors.

We research the electronic structure of LaO_(1-x)F_xFeAs in different F doping concentration using Virtual Crystal Approximation;discuss the doping effect on iron-based superconductor crystal structure and superconductivity.

Since the discovery of the superconductor F-doped LaFeAsO with Tc=26K at February 2008, and the Tc of some iron-based superconductor even up to 55Kwhich was found a few months later, besides a lot of new superconductors were found.

This article reviews nuclear magnetic resonance studies on iron-based high critical temperature superconductors carried out by the author\'s group.

In this paper, a review on the research progress in synthesis of iron-based superconducting materials is presented, including their synthesis methods and the key physical parameters, in each of iron-based superconductors\'s four main systems, "1111", "122", "111" and "11" systems, mainly in chronological order.