Among titanic acid compounds, the perovskite-type crystal structure, which is a titanic acid alkaline earth metal, is generally well known but there are also various titanic acid compounds with a layer or tunnel structure in which TiO6 octahedron and TiO5 trigonal bipyramid, as found in titanic acid alkali metals, are chained and share ridge lines. These crystal structures pave the way for synthesizing new compounds in the future.