Anosovite-Type V₃O₅: A New Binary Oxide of Vanadium

Abstract

The reaction of either V(2)F(6)·4H(2)O or a mixture of 60 wt % VF(2)·4H(2)O and 40 wt % VF(3)·3H(2)O with a water-saturated gaseous mixture of 15-20 vol % hydrogen in argon leads to the formation of a new polymorph of V(3)O(5) crystallizing in the orthorhombic anosovite-type structure. Quantum-chemical calculations show that the anosovite-type structure is about 15 kJ/mol less stable than the corresponding monoclinic Magnéli phase. In addition, there are no imaginary modes in the phonon density of states, supporting the classification of the anosovite-type phase as a metastable V(3)O(5) polymorph. Susceptibility measurements down to 3 K reveal no hint for magnetic ordering.

Chemical Reactions followed by in situ Neutron Powder Diffraction

“…Hydrogen is incorporated into [Pd 6 ] voids of a ZrAl 3 type structure (fourfold superstructure of the cubic close packing), for higher gas pressures [MPd 5 ] and later [M 2 Pd 4 ] are also occupied for M = Mg. [61] Electronic structure calculations show that this is driven by gaining Pd-H binding energy, however at the same time weakens the cohesion energy between the metal atoms. This is probably the reason, why the following rearrangement to a AuCu 3 type arrangement for MPd 3 , which can be envisaged as a gliding of structure blocks along ½ [110] (Figure 5) has got a low activation barrier [91] and proceeds at very mild conditions. Hydrogen occupies only [Pd 6 ] voids, i.e., the crystal structure is that of a cubic perovskite type, and can be removed by heat treatment in a vacuum, thus producing new polymorphs of the intermetallic in the AuCu 3 type, not accessible by other synthetic routes.…”

“…Bixbyite type V 2 O 3 and anosovite type V 3 O 5 can be prepared from vanadium trifluoride at elevated temperatures in an atmosphere of water-saturated hydrogen in an argon atmosphere, with 10 and 20 vol-% hydrogen, respectively. [109,110] By in situ neutron powder diffraction on the formation of bixbyite type V 2 O 3 starting with V 2 F 6 ·6H 2 O several intermediates were observed, one of which is a new compound, whose unexpected hexagonal bronze like structure could be solved from the in situ diffraction data. [111] Again, such knowledge of reaction pathways helps in improving the synthesis of metastable compounds.…”

Synthesis and characterization of metastable transition metal oxides and oxide nitrides

“…In most cases it is very difficult to obtain phase pure materials important for an unambiguous interpretation of the data from the properties measurements. During the last years we published on synthesis and characterization of four new metastable phases: bixbyite-type V 2 O 3 [1], anosovite-type V 3 O 5 [2], VO 2 (B)-type TaON [3], and anatase-type TaON [4]. Unfortunately, only anosovite-type V 3 O 5 can be synthesized as single phase [2].…”

“…During the last years we published on synthesis and characterization of four new metastable phases: bixbyite-type V 2 O 3 [1], anosovite-type V 3 O 5 [2], VO 2 (B)-type TaON [3], and anatase-type TaON [4]. Unfortunately, only anosovite-type V 3 O 5 can be synthesized as single phase [2]. All other samples contained large amounts of side phases leading to severe problems concerning the investigation of physical properties.…”

“…All other samples contained large amounts of side phases leading to severe problems concerning the investigation of physical properties. However, the crystal structures could be determined, also in combination with quantum-chemical methods [1][2][3][4]. Recently, we optimized the preparation techniques and in this contribution we present simple routes to phase pure bixbyitetype V 2 O 3 and VO 2 (B)-type TaON (γ-TaON) [5].…”