Crystal structure of a new polytype in the V–P–O system: is ω-VOPO4 a dynamically stabilised metastable network?

The crystal structure of δ-VOPO4 and its relationship to ω-VOPO4

“…Structurally, they share a rather low calculated density in comparison to other VOPO 4 polymorphs (3.0 () and 2.9 () [23] 3 () [25]). Although -VOPO 4 has an even lower density, it is not directly comparable as the crystal structure was determined at elevated temperatures [27]. As the PO 4 and VO 5 units in VOPO 4 can be considered to be relatively rigid, the variable V···O distance is one of the main factors contributing to the density variation.…”

“…Indeed, we find the same general arrangement and connectivity between VO 6 octahedra and PO 4 tetrahedra. Due to the peculiar disorder of the -VOPO 4 structure, which involves both phosphate and vanadyl oxygen positions [27], it cannot be displayed conveniently in a polyhedral fashion. Thus, we use a ball and stick model to depict the disordered  structure in Fig.…”

“…Thus, we use a ball and stick model to depict the disordered  structure in Fig. 2, while following Amorós et al [27] in using an idealized -VOPO 4 model with averaged oxygen positions for the polyhedral representation in Fig. 3.…”

“…The most extreme expansion of the unit cell would be achieved when both phosphate groups finally show a parallel orientation, i.e. when the vanadyl groups are [27]. Tick marks indicate the calculated peak positions.…”

“…More recently, these materials were also investigated in the field of lithium battery research [13][14][15][16][17][18][19]. Up to now, seven polymorphs of this compound have been described:  I [20],  II [20,21],  [22],  [1,23],  [1],  [24,25], and  [26,27]. However, compared to the significant interest in these materials, the accumulation of detailed crystal structure knowledge has been rather slow.…”