An EPR study of W5+ in a recently discovered triclinic tungsten bronze, Na0.33WO3

Abstract

A single crystal EPR study of W5+ in triclinic Na0.33WO3, a recently discovered compound, has been carried out at about 15 K and 9.2 MHz. The EPR spectrum consists of two strong resonances and several weaker resonances whose relative intensities are sample-dependent. The total W5+ concentration is approximately 1000 at. ppm. The principal g-tensor components and the 183W hyperfine splitting constants for the two strong resonances are |g1|=1.695±0.003, |g2|=1.659±0.003, |g3|=1.636±0.003 [|A2|≃(61±8)×10−4 cm−1] and |g1|=1.676±0.002, |g2|=1.630±0.002, |g3|=1.593±0.002 [|A3|≃(52±4)×10−4 cm−1] for resonance 1 and resonance 2, respectively. The hyperfine splitting constants could only be determined in a few orientations because of either lack of resolution or interference of weaker resonances. It is proposed that the observed resonances are due to different W5+ point defects in the Na0.33WO3 host. This work represents the first evidence of W5+ in the tungsten bronzes.

Improving the Selectivity of Photocatalytic NOx Abatement through Improved O2 Reduction Pathways Using Ti0.909W0.091O2Nx Semiconductor Nanoparticles: From Characterization to Photocatalytic Performance

“…The direct involvement of W-oxo species in electron storage was proven by diminishing the amount of W in the nanoparticles, which resulted in a lower stored electron concentration (Figure a,b). These observations are in agreement with results obtained by other researchers on TiO 2 /WO 3 mixed oxide systems. − The presence of W in oxidation states lower than 6 would make the oxide quasi-metallic or metallic, , which could be an independent confirmation of bronze-like chemistry. Indeed, EPR spectra at low magnetic fields (Figure ) exhibited a broad, asymmetric signal, typical of a Dysonian line, which is symptomatic of conduction electrons diffusing through a skin-depth layer …”

“…These observations are in agreement with results obtained by other researchers on TiO 2 /WO 3 mixed oxide systems. [24][25][26][27][28][29] The presence of W in oxidation states lower than 6 would make the oxide quasi-metallic or metallic 55,56 which could be an independent confirmation of bronze-like chemistry. Indeed, EPR spectra at low magnetic fields ( Figure 11) exhibited a broad, asymmetric signal, typical of a dysonian line 57 which is symptomatic of conduction electrons diffusing through a skin depth layer.…”

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions

“…Namely, the intense, broad signal in Figure a visible below 20 K is a characteristic powder spectrum of half-spin rare-earth ions occupying several anisotropic, magnetically nonequivalent sites. , However, apart from that unique cerium signal, we do not see any clear signal from coexisting W 5+ ions, which are naturally occurring, d-block charge-compensators, according to XPS data in Figure d. The signal should appear at about 3400 G owing to the g -factor = 1.989. , It may be covered by the stronger Ce 3+ signal since W 5+ concentration is low. Since the material is diluted paramagnet with anisotropic (Ce–O, W–O) defects scattered randomly throughout the microcrystalline lattice and these ions are also PL-active, a parallel experiment was launched to assess their behavior.…”

“…The signal should appear at about 3400 G owing to the g-factor = 1.989. 149,150 It may be covered by the stronger Ce 3+ signal since W 5+ concentration is low. Since the material is diluted paramagnet with anisotropic (Ce−O, W−O) defects scattered randomly throughout the microcrystalline lattice 151 and these ions are also PL-active, a parallel experiment was launched to assess their behavior.…”

On the stability of MOPO4 structure types with M: V, Mo, Nb, W, Ta, Sb

“…Die experimentell erhaltenen g-Werte stehen im Einklang mit der Orbitalaufspaltung eines gestauchten Oktaeders (g ∥ ̸ = g ⊥ < g e ; vgl. Literatur [188,189]). Anhand dieser Werte kann der Stevensorbitalreduktionsparameter k mit k ∥ = 0,71 und k ⊥ = 0,88 unter Verwendung von λ 0 (W 5+ ) = 2300 cm −1 mit der Abraham-Pryce-Näherung ermittelt werden (vgl.…”