Abstract
The real stucture of a new crystalline high temperature phase, metastable at room temperature, in the system sodium โ bismuth โ oxygen, ฮฒ-Na~3~BiO~4~, was determinated using high resolution X-ray powder diffraction, pair distribution function analysis, and high resolution transmission electron microscopy. ฮฒ-Na~3~BiO~4~ was synthesized by anodic oxidation of bismuth(III)-oxide in a sodium hydroxide โ lithium hydroxide melt. The average crystal structure of ฮฒ-Na~3~BiO~4~ at ambient conditions (R__3__m, a = 3.32141(9) ร
, c = 16.4852(5) ร
) is structurally related to ฮฑ-NaFeO~2~ with metal layers almost statistically occupied in a Na:Bi ratio of 3:1. Analysis of the long-range order on the bulk material by Rietveld refinement led to approximately Na:Bi ratios of 2:1 and 4:1, in consecutive metal layers, while a detailed analysis of the local order by means of the pair distribution function revealed the existence of almost pure sodium layers and mixed 1:1 โ sodium:bismuth layers. Complementary studies on single crystallites using high resolution transmission electron miscroscopy exhibited a complex domain structure with short-range ordered, partially ordered, and long-range ordered domains.