Cesium polytungstate in sputtered solar control films. I. Microstructure and optical properties

Abstract

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.

X-ray Photoelectron Spectroscopic Study of Reduced Alkali Tungsten Oxides with Localized and Delocalized Electrons

“…Since the hexagonal lattice parameters of Cs 4 W 11 O 35 (not shown here) locate at far a -rich and c -rich coordinates at (7.5064, 7.7356) in Figure a, the small deviation toward a -rich and c -rich coordinates of the A-root HTBs is suspected to be due to the shift in the internal structure of Cs 0.32 WO 3– y toward Cs 4 W 11 O 35 . This orthorhombic shift of HTB was observed to be caused microstructurally by an increased interplanar spacing due to the planar W-deficiencies introduced on the prismatic planes of HTB. , Therefore, the small deviation in the lattice parameters toward Cs 4 W 11 O 35 implies the presence of remnant W-deficiency in the A-root HTBs.…”

“…This orthorhombic shift of HTB was observed to be caused microstructurally by an increased interplanar spacing due to the planar W-deficiencies introduced on the prismatic planes of HTB. 37,38 Therefore, the small deviation in the lattice parameters toward Cs 4 W 11 O 35 implies the presence of remnant W-deficiency in the A-root HTBs.…”

Resolving old problems with layered polytungstates related to hexagonal tungsten bronze: phase formation, structures, crystal chemistry and some properties

“…It is noteworthy that microphases of these homologous series with n = 3, 4 and 5 were observed on the high-angle annular-dark-field (HAADF) images of the HTB-like K x WO 3+ y nanosheets 65 and Cs x WO 3+ y films. 82 The ideal compositions of these microphases in accordance with the general formula of the homologous series should be A 5− x W 11 O 35 = A 5− x W 6+ 10+ x W 5+ 1− x O 35 (0 ≤ x ≤ 1), A 3− x W 7 O 22 = A 3− x W 6+ 6+ x W 5+ 1− x O 22 (0 ≤ x ≤ 1) and A 7− x W 17 O 53 = A 7− x W 6+ 14+ x W 5+ 3− x O 53 (0 ≤ x ≤ 2) for n = 3, 4 and 5, respectively. Formation of such phases is also facilitated by alkali-deficient sites in the HTB-like polytungstates, which appear to vary widely.…”

“…It should also be noted that the HTB-like polytungstates may be the by-products of preparing HTB-type A x WO 3 (A = K, Rb, Cs) in the presence of oxygen, water, oxygen-containing solutions and alkaline impurities, as can be seen from the data. [62][63][64]76,82,94 Therefore, it is likely that the nanowire and nanosheet forms of such bronze complexes, which were often observed in these works, may in fact be the corresponding layered HTB-like polytungstates or their intergrowth phases with HTB, but not pure hexagonal bronze nanoforms.…”

“…It is noteworthy that microphases of these homologous series with n = 3, 4 and 5 were observed on the high-angle annular-dark-field (HAADF) images of the HTB-like K x WO 3+y nanosheets 65 and Cs x WO 3+y films. 82 The ideal compositions of these microphases in accordance with the general formula of the homologous series should be…”