Vanadium pentoxide and vanadium oxide bronzes—Structural chemistry of single (S) and double (D) layer MxV2O5 phases
1992; Elsevier BV; Volume: 100; Issue: 2 Linguagem: Inglês
10.1016/0022-4596(92)90097-f
ISSN1095-726X
Autores Tópico(s)Polyoxometalates: Synthesis and Applications
ResumoInvestigation of the details of the V2O5 crystal structure shows the vanadium coordination to be purely square pyramidal SP, the single [V2O5] layer S being built up by endless double strings of VO5 SP associated by corner sharing. This unit allows to describe all the VOB's structures exhibiting S layers, i.e., α-MxV2O5 (M = all elements), ε-, δ-, γ-LixV2O5, α′-NaxV2O5, Cu0.64V2O5. The structural mechanisms which govern the phase transitions ε → δ, δ → γ have been described, as well as the transformations by crystallographic shears, slips, and VO5 SP reversal of ε (or α) into the 3-D networks of β or β′-MxV2O5 phases. The complete LixV2O5 system versus f(T, x) is described and the evolution of the cell parameters for ε and γ phases is accounted for by introducing the puckering angle μ of the S layers. The demonstration of the slipping of the S layers quantified by shift Δ, expressed as a fraction or unit of the height of an octahedron, has made it possible to propose various original stackings for these layers; some ideal structures are described. A mechanism explaining the M intercalation between S layers shows that for large cations new layers are formed after shrinkage of two S layers giving double [V2O5] layers D of the D4 and D4M types built up by endless quadruple strings and DZ type obtained from cross-linked double strings of VO6 octahedra sharing edges and corners. This assumption is supported by the structure of the new VOB, τ-Na0.70V2O5, which is an intergrowth of the D4 and DZ layer types. Using these units in combination with Δ slips has permitted a unifying description is given for all known structures: δ-AgxV2O5, δ-SrxV2O5, δ-K0.5V2O5, ν-Ca0.60V2O5, ν-K0,62V2O5, ν-Rb0.40V2O5, ν-(NH4)0.50V2O5, ε-CuxV2O5, ϱ-K0.50V2O5, …, and many other possibilities are suggested.
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