Abstract:
In this study the solid state chemistry of some metavanadate compounds has been further explored. Firstly the decomposition of NH4vo3 was re-investigated and in particular the first reaction step and the reaction product of this decomposition were studied in detail. The structure of (NH4)2v6o16 was determined as monoclinic, space group P21/m. Vibrational spectra of the v6o16 2- anion were analyzed by means of group theoretical analysis of the normal vibrations. Raman spectroscopy was used to follow the kinetics of the abovementioned decomposition step. This method directly monitors the amount of reactant present. The decomposition mechanism was determined and the activation energy of the reaction was calculated. Although the crystal structures of NH4vo3 and (NH4)2v6o16 are known, little is known about the nature of hydrogen bonds in these compounds. Since the Raman active N-H bonds in NH 4vo 3 are of very low intensity, making it very difficult to study isotopically dilute ions, the low temperature infrared spectra of the N-D stretching modes of isotopically dilute NH3D+ ions in both NH4vo3 and (NH4)2v6o16 are reported here. These results indicate that both normal and bifurcated hydrogen bonds occur in NH4vo3 and (NH4) 2v6o16 In the alkali metal metavanadates no evidence of the dielectric phase transition in KV03 could be found by means of Raman spectroscopy and X-ray powder diffraction. The phase transition in NaV0 3 involving changes in the crystal structure was investigated by means of far-infrared spectroscopy. Infrared and Raman spectra of the solid solutions Na(V0.66 P0.34 )VO3 , {Na0.88 K0.12 )V03 and {Na0.5 K0.5)VO3 are reported in comparison with those of the end member phases. Translation modes of the cations could accordingly be identified unambiguously. However, the product obtained from the high temperature reaction of an alkali metal metavanadate and a lanthanide oxide is not a solid solution. Infrared and Raman spectroscopy, X-ray powder diffraction and scanning electron microscopy with EDX-analysis revealed that the lanthanide orthovanadate is formed with the alkali metal oxide as a probable second product. Emission and/or absorption spectra of LnV0 4. {Ln = Er, Eu, Nd) are reported together with a vibrational analysis and infrared and Raman spectra of the VO3/4 in the zircon phase.
