Hydrothermal Synthesis and Crystal Structure of a Novel Bismuth Oxide: (KSr)(NaCaBi)O.

A novel distorted perovskite-type (KSr)(NaCaBi)O was prepared by a hydrothermal method using the starting materials NaBiO·HO, Sr(OH)·8HO, Ca(OH), and KOH. Single-crystal X-ray diffraction of the novel compound revealed a GdFeO-related structure belonging to the monoclinic system of the space group with the following cell parameters: = 11.8927 (17) Å, = 11.8962 (15) Å, = 8.4002 (10) Å, and β = 90.116 (9)°. The final -factors were obtained as = 0.0354 and w = 0.0880 (using all the data). K and Sr ions were distributed at four types of A-sites. On the other hand, four Bi-sites (Bi1, Bi2, Bi3, and Bi4) were occupied by four Ca ions (Ca1, Ca2, Ca3, and Ca4), and the first three B-sites were occupied predominantly by Bi with Na ions. The forth B-site was occupied predominantly by the Ca ion with Bi ions. Two types of B-sites, thus forming tilted distorted (Na/Ca/Bi)O and (Bi/Ca)O octahedra, have an ordering of 3:1 represented as (K/Sr)(Na/Ca/Bi)(Bi/Ca)O. The distorted (Na/Ca/Bi)O and (Ca/Bi)O octahedra formed a perovskite-type network by corner sharing with features closely matching those of a GdFeO-type structure. The novel compound is the first example of a perovskite-type bismuth oxide containing only Bi in a system without a Ba atom and has a unique ordering (3:1) of the B site. The compound showed photocatalytic activity for phenol degradation under visible light irradiation.