Vanado phosphates

Substitution of the co-ordinated oxygen atoms by divalent radicals yields the various heteropoly-acids. The vanado-phosphates, for instance, are derivatives of the hypothetical phosphato-acid H7[P06],... 

Vanado-phosphates.—Alkali vanado-phosphates are numerous, and contain from one to twelve molecules of vanadium pentoxide in combination with one molecule of phosphorus pentoxide. Those with high vanadium pentoxide content are red, crystalline substances, and are called pwpureo-compounds those with low vanadium pentoxide content form yellow crystals, and are styled Iwteo-compounds.2... 

Vanado-arsenates.—The salts of this class which have hitherto been prepared are all of low vanadium pentoxide content compared with the amount of arsenic pentoxide present. They correspond, therefore, to the luteo vanado-phosphates. Three series are known. The... 

In 2013, the D-HMQC technique has been involved in the structural characterisation of vanado-phosphate-based system within the 50Na2O-3cV2O5-(50 — 3c)P20s composition line [53]. These glasses have already been investigated by Raman and ID P and NMR spectroscopies [54,55]. The results suggest that the network was built by interconnected vanadate and phosphate polyhedra but no direct evidence about the presence of P—O—V bond was available. D-HMQC experiment was applied... 

Figure 4.6 Structure of the Pb4(V0)2(P04)3 compounds (A) and structure of the vanado-phosphate network (B). D-HMQC (9.4 T C0r=20 kHz SFAM2 acquired in 56 h)...

G. Tricot, H. Vezin, Description of the intermediate length scale structural motifs in sodium vanado-phosphate passes by magnetic resonance spectroscopies,. Phys. Chem. C 117 (2013) 1421-1427. 

Vanado-phosphate glasses (VPGs) are well known for their semi-conductive behaviour [72]. In the last decades they were widely studied in order to understand the mechanism underneath their electronic properties. The electronic conductivity was correlated to small polaron hopping between vanadium ions with different valence state [86], favoured by their electronic configuration [87]. In VPGs, vanadium atoms are mainly characterized by two oxidation states, 4+ and 5+, and the and based interconnected polyhedra become the preferential path for the polaron hopping [88]. Therefore, the relative amount of these two species (V" + and V +), which is usually expressed as V" +A tot ratio, influences the final electrical properties of VP systems [86, 89]. 

Xhe V +-0 PDF curve, reported in Fig. 8.3, shows the presence of a shoulder at about 1.65 A that can be associated to the presence of the typical vanadyl (V=0) bonds that are found in vanado-phosphate systems. 

As previously reported, the peculiarity of alkali vanado-phosphate glasses is ascribed to the mixed electronic-ionic conductivity. The electronic conductivity is due to the small polaron hopping between the TM ions with different valence state and it could be related to the presence of V +-0-y + species in the glass network. For NaVP systems, TableS.lO reports the various contributions that are included in the V-O-V linkages. It could be highlighted that the increase of V content results in a major number of V -O-V " linkages, which might be correlated to an increase of the electronic conductivity. 

In the present work, MD simulations were used to study the structure of alkali vanado-phosphate glasses providing insight into the short and medium range order of the glass network and to the role of the vanadium ions and their environment in the glass matrices. 

G. Ori, C. Mugoni, G. BrogUa, C. Siligardi, M. Montorsi, Short- and medium-range order structure of alkali vanado-phosphate glasses a Molecular Dynamics study (Submitted) (2014)... 

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