Synthesis of non-stoichiometric Bi2O4-x by oxidative precipitation

Bi2O4-x, a Bi mixed-valence phase was prepared at 95 degrees C, by a precipitation process, in a basic medium with a highly oxidizing K2S2O8/Na2S2O8. This phase has a low thermal stability as it decomposes below 400 degrees C in a multiple step process by some O-2 losses prior to finally transforming into gamma-Bi2O3. The as-prepared powders are 50-60 nm in size with a narrow size distribution. Optical spectra of Bi2O4-x exhibit a broad absorption band with a band gap of similar to 1.4 eV as compared to 2.61 eV for Bi2O3. The composition of this non-stoichiometric phase, which crystallizes in cubic fluorite related structure with a cell parameter of 5 538(3) angstrom, is Bi2O3.65 +/- 0.10. (c) 2006 Elsevier Ltd. All rights reserved.