Variation of oxygen content in selected potassium fluorido-oxido-tantalate phases

The compound K3[TaO4]∙K3[TaF4O2] crystallises in a tetragonal system (space group I-4) with cell parameters a = 6.2220(3) Å and c = 8.7625(34) Å, respectively. The crystal structure consists of two anions, [TaO4]3− and [TaF4O2]3− and cations K+. The tantalum atoms lie in special positions and serve as centres of both anions, which are substitution disorders. XPS measurements confirmed the existence of different binding energies corresponding to the different bonds of TaO and TaF. Oxygen is bound more strongly in [TaF4O2]3−. By combination of single crystal analysis, XRD, SIMS and XPS it was suggested that previously reported cubic phase K3TaOF6 is in fact K3TaO2F4 and previously reported tetragonal phase K3TaO2F4 is in fact K3[TaO4]∙K3[TaF4O2].

The disordered parts of anion [TaF4O2]3− are drawn solid line (main part) and open solid line (minor part).Figure optionsDownload as PowerPoint slideHighlights
► Single crystal analysis of K3[TaO4]K3[TaF4O2].
► The crystal structure consists of two anions, [TaO4]3− and [TaF4O2]3− and cations K+.
► XRD, SIMS and XPS supporting spectroscopies.