Oxygen vacancies and pseudo Jahn‐Teller destabilization in cesium‐doped hexagonal tungsten bronzes

Abstract

Structural and compositional changes of Cs‐doped hexagonal tungsten bronzes (HTB) with respect to variations in oxygen deficiency and alkali content have been investigated in detail through x‐ray diffraction Rietveld analysis, x‐ray photoelectron spectroscopy, and Raman spectroscopy. Cs‐HTB crystallized in a reductive atmosphere is evidenced to generally contain plenty of oxygen defects, and a general formula, CsxWO3−y (0.20 ≤ x ≤ 0.32, 0 < y ≤ 0.46), is proposed. Lattice parameters of Cs‐HTB are observed to vary according to the relation, c (Å) = −3.436a (Å) + 33.062. The coordinated modification of W–O octahedral dimensions suggests the origin of the structural change with increasing x and y to be a destabilization of the pseudo Jahn‐Teller distortion due to donated electrons. The dimensional change of lattice due to electrons emitted from oxygen defects is appraised only 1/18 as that due to electrons from doped alkali ions, suggesting that most electrons from oxygen defects should be localized in Cs‐HTB.

Cesium polytungstates with blue-tint-tunable near-infrared absorption

“…Dispersions of neutral-toned In 2 O 3 : Sn (ENAM Optoelectronic Material Co., Ltd., Funan, China; hereaer referred to as ITO) and bluish fully-reduced Cs-HTB prepared by the GFR process 19 (hereaer referred to as CWO™) were prepared as color-tone references.…”

“…X-ray photoelectron spectroscopy (XPS) was performed using a Versa Probe II instrument (Ulvac-phi Inc., Chigasaki, Japan). As ion cleaning is known to reduce the sample surface, 19 the measurements were performed on freshly as-produced powders. Okada et al 19 conrmed that Cs-HTB powders qualitatively give the same results as the bulk vacuum-cleaved surface.…”

“…As ion cleaning is known to reduce the sample surface, 19 the measurements were performed on freshly as-produced powders. Okada et al 19 conrmed that Cs-HTB powders qualitatively give the same results as the bulk vacuum-cleaved surface. The precise position of the Fermi energy, E F , in the bottom of the conduction band was calibrated by evaporating Au on the second measurement.…”

“…In the conventional gas ow reduction (GFR) method 19 or the vacuum encapsulation method, 24 the crystallization of Cs 0.32 -WO 3Ày and oxygen reduction proceed in parallel with the hightemperature reduction. On the other hand, when polytungstate crystals are reduced at high temperature, high crystallinity is expected from the early stages of reduction, which was considered as an advantage of the Wöhler's method.…”

“…17,18,40 The V O s have been analyzed to play a major role in the LSPR and polaronic excitation. 19,20 On the other hand, the visible transparency of Cs-HTB nanoparticles, which is highest among the HTBs, has not been considered in detail, and its origin remains unclear. In addition, the slight bluish tint accompanying the transmitted light must be resolved in actual applications.…”