Zintl and polar intermetallic phases are compounds intermediate among classical metals, ionic crystals, and covalent crystals and they exhibit metallicity, ionicity, and covalency simultaneously. It is challenging to rationalize the structures of these phases because we cannot simplistically apply the rules that are applicable to metallic, ionic, or covalent solids.

This dissertation includes our synergic works between experiments and quantum mechanical calculations in rationalizing the structures of Zintl and polar intermetallic phases. By studying alkali metal trielides and alkali metal gold bismuthides, we investigated the competition among metallicity, ionicity, and covalency and its structural effects, through which we made several supplements to the Zintl-Klemm formalism and deepened our understanding of the structures of Zintl and polar intermetallic phases.

We also studied the EuAgxAl11-x systems, addressed the "coloring problem", which occurs frequently in Zintl and polar intermetallic phases, and rationalized the competition between the BaCd11- and the BaHg11-type structures.

Some preliminary works were also done with the Gd5Tt4 systems to rationalize their structural variations.