Hydrothermal synthesis and crystal structure of a novel double-perovskite-type bismuth oxide with 3 : 1 ordering at the B-site

A low-temperature hydrothermal method was successfully used to synthesize a novel bismuth oxide Ba₄Bi₃NaO₁₂. Here, NaBiO₃·nH₂O was used as one of the starting materials. Single-crystal X-ray diffraction revealed the triclinic double-perovskite-type structure of the novel compound with a P1 (No. 2) space group. The cell parameters of the compound were as follows: a = 8.5415 (2) Å, b = 8.5421 (2) Å, c = 8.5441 (2) Å, α = 89.996 (1)°, β = 89.995 (1)°, and γ = 90.016 (1)°. The final R-factors were found to be R₁ = 0.0202 and wR₂ = 0.0476 (all data). In the crystal structure, the A-site was completely occupied by Ba²⁺ ions. There were eight B-sites (Bi1, Bi2, Bi3, Bi4, Bi5, Bi6, Bi7, and Bi8), among which the Bi5 and Bi6 sites were occupied by Bi atoms and the others were randomly occupied by Bi with Na atoms. Two types of B-sites formed tilted distorted octahedral BiO₆ and (Na/Bi)O₆ with an ordering of 3 : 1, which are analogous to the previously reported (K_0.2Sr_0.8)(Na_0.01Ca_0.25Bi_0.74)O₃. Octahedral BiO₆ and (Na/Bi)O₆ formed a perovskite-type network by corner sharing. This newly synthesized perovskite-type bismuth oxide exhibited a unique ordering of 3 : 1 at the B-site. This compound exhibited photocatalytic activity toward phenol degradation under visible-light irradiation. The semiconducting nature of this novel compound was investigated using a first-principles study.