The general formula of a phase relation between well-known bismuth layer-structured ferroelectrics (BLSF) such as Bi3TiNbO9, Na0.5Bi2.5Nb2O9, Bi4Ti3O12, and Na0.5Bi4.5Ti4O15 including perovskite compounds (Bi0.5Na0.5) TiO3 and NaNbO3, that is, Na(m-3+x)/2 Bi(m+5-x)/2 Ti m-x Nb x O3m+3 (2≤m≤5), was discussed to form the layer structure with the numbers m=3, 4 and 5 of layer, where x is the number of Nb ions in the layer structure and 1≤x≤2 for m=2 and 0≤x≤m for 3≤m≤5. A new BLSF series is found for m=3 and x=1, 2 and 3. The ferroelectricity for m=4 (x=3 and 4) was very weak and no single phase with m=5 was obtained.

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A small angle X-ray diffraction using synchrotron radiation, microscopic Raman spectroscopy and a high-resolution TEM were used to characterize superlattices (SLs) grown at 500, 600, and 700°C. The periodicity of the SLs was not degraded, but transition-layer thickness increased with the growth temperature. The transition layer was revealed to be atomic-layer steps with a monolayer per length ,100 A for the 500°C-, and with one or two monolayers per length less than 30 A for the 700°C-grown SLs.