The surface structure of the metallic sodium tungsten bronze Na0.667WO3(001)

The band structure of WO3and non-rigid-band behaviour in Na0.67WO3derived from soft x-ray spectroscopy and density functional theory

“…WO 3 single-crystals were grown by crystallization from a PbF 2 /NaF flux. Crystals from the same growth batch have been extensively studied by LEED, STM, and photoemission [10,11,29]. Na 0.67 WO 3 single-crystals were grown by the electrolytic reduction of a molten mixture of WO 3 and Na 2 WO 4 .…”

“…For x ≥ 0.42, Na x WO 3 is metallic with a cubic perovskite-type structure [4,11]. The sodium atoms occupy a fraction of the 12-coordinate interstitial A-sites in the WO 6 octahedra framework [4,[11][12][13]. The crystal lattice parameter increases linearly with Na doping concentration (by ∼2% for the fully intercalated x = 1 compound), as determined by x-ray diffraction [14].…”

“…Na x WO 3 shows a rich phase diagram with different doping level x [4]. For x ≥ 0.42, Na x WO 3 is metallic with a cubic perovskite-type structure [4,11]. The sodium atoms occupy a fraction of the 12-coordinate interstitial A-sites in the WO 6 octahedra framework [4,[11][12][13].…”

“…Among the experimental techniques of condensed matter physics, x-ray spectroscopy has an advantage of combining both electron and photon spectroscopic probes, which can measure both surface-and bulk-electronic structures, respectively. X-ray and ultraviolet photoemission spectroscopies (XPS and UPS) have been used to explore the valence band (VB) structure and the nature of the CB states in Na x WO 3 [4,10,11,13,25]. Angle-resolved photoemission spectroscopy (ARPES) has been employed to measure the band dispersions and Fermi surfaces in metallic Na x WO 3 with a range of x [4,13].…”

Novel mesoscale defect structure on NiO(100) surfaces by atomic force microscopy

“…The surface properties of these materials, in turn, are often highly infl uenced by surface defect structure [1], [2], [3] and [4]. Defects have been shown to be important in TMO electronic, magnetic, and chemical properties and span a wide range of scale, including oxygen vacancies [1], [2], [3], [5], [6], [7] and [8], metal interstitials and adatoms [1] and [9], crystal shear planes [4] and [10], step-defects [4], [10], [11] and [12], meso-to macroscopic scale pits, protrusions, and related large-scale imperfections [13], [14] and [15], the latter of which often have a complicated morphology with a range of atomic-scale defects in their own right [16], [17], [18] and [19]. The surface defect nature may be infl uenced by bulk structure and impurity concentration [1], [4] and [20], introduced by surface preparation methods [12] and [21], or result from chemical reactivity and corrosion properties of the substrate surface [1], [2], [3], [5], [6] and [22].…”