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Ga2.52V2.48O7.33(OH)0.67, a synthetic member of the nolanite/akdalaite-type family of oxyhydroxides containing trivalent vanadium

DOI: 10.1016/j.jssc.2020.121396 DOI Help

Authors: Daniel S. Cook (University of Warwick) , Martin R. Lees (University of Warwick) , Janet M. Fisher (Johnson Matthey Technology Centre) , David Thompsett (Johnson Matthey Technology Centre) , Richard I. Walton (University of Warwick)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Solid State Chemistry

State: Published (Approved)
Published: April 2020
Diamond Proposal Number(s): 13841

Abstract: The oxyhydroxide Ga2.52V2.48O7.33(OH)0.67 is prepared by reaction between Ga metal and Na3VO4 in a 1:1 monoethanolamine:water mixture at 240 °C. Powder neutron diffraction shows the material to be isostructural with the minerals nolanite and akdalaite, with cations occupying tetrahedral and octahedral interstitial sites in a hexagonal close-packed array of oxide/hydroxide (P63mc, a = 5.7906(2) Å, c = 9.2550(5) Å). Rietveld refinement against the data shows that Ga preferentially occupies tetrahedral sites, as well as some octahedral sites, and hence all V is octahedrally coordinated. The oxidation state of vanadium is confirmed as close to V3+ using V K-edge X-ray absorption near-edge structure spectroscopy, consistent with the refined chemical composition. The material is metastable, dehydrating around 300 °C and then decomposing above 500 °C, as shown by thermogravimetric analysis and thermodiffraction. The oxide Ga2.52V2.48O8 produced after dehydration at 300 °C is shown to contain a larger proportion of V4+ than the parent oxyhydroxide, to ensure charge balance, but the essential hexagonal structure is maintained. Variable temperature magnetisation measurements show that although both materials appear to obey the Curie-Weiss Law at high temperatures, at low temperatures the inverse susceptibility curves are non-linear. There is, however, no evidence for strong magnetic exchange and the extracted effective moments are consistent with the presence of more V3+ in the oxyhydroxide compared to the oxide.

Journal Keywords: Solvothermall; Gallium; Vanadium; Oxide; Synthesis

Subject Areas: Chemistry

Instruments: B18-Core EXAFS

Other Facilities: ISIS

Discipline Tags:

Chemistry Inorganic Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Near Edge Structure (XANES) X-ray Absorption Spectroscopy (XAS)