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.

No abstract

Revisiting Wöhler's method (1824), Cs-doped tungsten bronzes were synthesized by reducing Cs-polytungstate at high temperature, and were pulverized into nanoparticles for determining their optical properties.

In Cs-doped hexagonal tungsten bronzes (Cs-HTBs), X-ray diffraction–Rietveld analysis has revealed that an increase in the alkali dopant and oxygen vacancies (VO) elongate the c-axis, contract the a-axis, and decrease the deviations of the W–O distance and W coordinates from those of a regular WO6 octahedron. These structural changes are interpreted as a destabilization of pseudo-Jahn–Teller (PJT) distortion by electron donation from Cs+ and VO. A dramatic difference is observed in the destabilization efficiency between the donated electrons from Cs+ and VO, suggesting that the former and latter electrons should be delocalized and localized, respectively. First-principles density functional theory calculations using optB86b-vdW functionals reproduced the behavior of c-axis elongation and a-axis contraction by Cs doping. The projected orbital density of states indicates that the Cs-derived electrons are donated to W-5dyz and W-5dzx orbitals to extend along the c-axis, whereas the VO-derived electrons are donated to W-5dxy and W-5dx2−y2 orbitals to strongly localize in the a–b plane. In HTBs, an anisotropic increase and decrease in the t2g* antibonding electrons from the doped alkali are concluded to induce the anisotropic structural change in PJT distortions.

Sputtered thin films with strong near-infrared absorption and high visible transmission and electrical resistivity (≥102 Ω cm) have been obtained using highly conductive cesium tungsten bronze targets. The origin of the low electrical conductivity and high near-infrared absorption of the films has been investigated by focusing on internal defects and reported in two parts. In Paper I, the optical and electrical properties of the films and their microstructural characterization using x-ray diffraction and high-resolution transmission electron microscopy are presented. Abundant planar W and Cs defects were found on hexagonal prismatic planes that locally expanded the defect plane and triggered the hexagonal-to-orthorhombic crystallographic transition. These cationic defects diminished conduction electrons and suppressed electrical conduction, whereas oxygen vacancies generated W5+-trapped electrons to activate polaronic excitations for strong near-infrared absorption.

LaB6 nanoparticles are widely used as solar control materials for strong near-infrared absorption and high visible transparency. In order to elucidate the origin of this unique optical property, first-principles calculations have been made for the energy-band structure and dielectric functions of R(III)B6 (R(III) = Sc, Y, La, Ac). On account of the precise assessment of the energy eigenvalues of vacant states in conduction band by employing the screened exchange method, as well as to the incorporation of the Drude term, dielectric functions and various physical properties of LaB6 have been reproduced in excellent agreement with experimental values. Systematic examinations of dielectric functions and electronic structures of the trivalent metal hexaborides have clarified the origin of the visible transparency and the near-infrared plasmon absorption of R(III)B6 nanoparticles.

To control the electrochemical properties of LiNi 0.35 Mn 0.30 Co 0.35 O 2 (NMC) acting as a positive electrode material, Ni 0.35 Mn 0.30 Co 0.35 (OH) 2 precursors with different morphologies were synthesized by controlling the dissolved oxygen concentration during coprecipitation. As the dissolved oxygen concentration increases, precursor particles become more porous and have higher specific surface area. X-ray absorption spectroscopy clearly shows that only the Mn valence in the precursors increased with increasing dissolved oxygen concentration. X-ray diffraction patterns of the precursor synthesized under a high dissolved oxygen concentration suggested the formation of oxyhidroxide. The morphology of NMC synthesized using the developed precursors resembled that of the precursors. NMC with dense morphology exhibited high volumetric energy density, while that with porous morphology exhibited a high discharge capacity and rate performance without any cycle performance drawbacks. We expect that this simple method of morphology control by control of precursor dissolved oxygen concentration can be applied to improve the electrochemical properties of positive electrode materials with a wide range of Mn-containing compositions.

In a series of Cs-doped tungsten oxides that underwent different degrees of reduction, new components and behaviors were found in X-ray photoelectron spectroscopy (XPS) signals of O−1s, W−4f, and Cs−3d and analyzed in terms of oxygen vacancies (V O s) and electron localization with the aid of first-principles calculations. Orthorhombic Cs 4 W 11 O 35 was reduced at high temperature to transform it to hexagonal tungsten bronze with increasing W 5+ trapped electrons, as detected in W−4f. The binding energy of W 5+ −4f showed a distinct redshift toward low saturation values that was implied to be due to W 5+ alignment on the hexagonal prismatic planes. The V O enthalpy of formation and the Bader charge calculated for each atom site supported this view, by identifying the preferred sites for V O and W 5+ on (020) in Cs 4 W 11 O 35 . The W 5+ component was newly admitted in O−1s at 531.25−531.94 eV and 532.35−533.04 eV, while the carbonation contributions were eliminated using C−1s deconvolution. In Cs−3d, a V O -related extra component was found on the high-energy side, which grew with increasing reduction time. These observations and calculations supported the proposition that electrons emitted from Cs should be delocalized, and those from V O s should be both localized and delocalized in Cs-doped tungsten oxides.