Characterisation of WO 3-, V 2O 5-, and P 2O 5-doped bismuth oxides by x-ray diffraction and Raman spectroscopy

Abstract

The doped-bismuth oxide compounds of 7(Bi 2O 3)–2(WO 3), 3(Bi 2O 3)–(WO 3), Bi 23V 4O 44.5 and Bi 23P 4O 44.5 were prepared by the solid state method. Phase composition of these oxides was determined using x-ray diffraction and Raman spectroscopy. Raman spectroscopy showed the 7(Bi 2O 3)–2(WO 3) and 3(Bi 2O 3)–(WO 3), compounds to have similar structures most likely tetragonal. While, Bi 23V 4O 44.5 and Bi 23P 4O 44.5 are reported as belonging to the same triclinic phase, they were observed to have differing spectra and hence structures. Bi 23V 4O 44.5 showed a spectrum with strong bands at 54, 311 and 820 cm −1 similar to the orthorhombic Bi 38Mo 7O 78 or monoclinic Bi 6Mo 2O 15 phases, whereas, the Bi 23P 4O 44.5 phase has a much simpler spectrum with a strong band at 131 cm −1. XRD of both the tungsten doped-bismuth oxide compounds showed the same tetragonal structure. With increase in temperature the pattern of the 7(Bi 2O 3)–2(WO 3) system remained constant up to 1123 K, whereas that for 3(Bi 2O 3)–(WO 3) undergoes a transition to a more symmetric structure above 973 K. The XRD patterns of Bi 23V 4O 44.5 and Bi 23P 4O 44.5, show a triclinic pattern, however the Bi 23P 4O 44.5 pattern differs in that there are several extra peaks at d=2.35849, 2.04542, 1.44252 and 1.43884 Å, likely due to either secondary phase formation or a lowering of symmetry. Both phases are stable to 1123 K, however a few small peaks are observed for the Bi 23P 4O 44.5 compound above 973 K.