Syntheses, optical properties and electronic structures of copper(I) tantalates: Cu5Ta11O30 and Cu3Ta7O19

NaCu(Ta1−yNby)4O11 solid solution: A tunable band gap spanning the visible-light wavelengths

“…The synthetic procedures and methods investigated in this work were built starting from our previous synthetic work in the Cu 2 O-Ta 2 O 5 and Cu 2 O-Na 2 O-Ta 2 O 5 systems [24,25], as well as on the research of Jahnberg on layered copper(I)-tantalates having the general formula A x Ta 3n þ 1 O 8n À 3 [27,34,35]. In the Cu 2 O-Ta 2 O 5 system, significant synthetic difficulties were reported by Jahnberg for the separation of the four observed tantalates, i.e., Cu 2 Ta by single crystal XRD.…”

“…Their meta-stability is presumably based on their closely interrelated layer-stacking structural motives, and on the varying amounts of Cu(I) vacancies in the structures that exist to meet charge-balance requirements. Recently we were able to isolate Cu 3 Ta 7 O 19 as a pure phase using CuCl as a flux [24]. For the previously reported (Na 1 À x Cu x ) 2 Ta 4 O 11 solid solution, it was found that the percent of Cu(I) vacancies was an important factor for not being able to prepare the 'Cu 2 Ta 4 O 11 ' (i.e., x¼1) composition [25].…”

“…The excitations across the band edges are found to arise from metal-to-metal charge transfer transitions between electron-donating d 10 and electronaccepting d 0 electron configurations. Our efforts in this field have recently focused on Cu(I)-containing solids [23][24][25], and which remain almost entirely unexplored for their optical properties or potential for visible-light photocatalysis. Our photoelectrochemical characterization of these compounds has shown that the valence bands formed by the Cu(I) 3d 10 orbitals can be suitably positioned to meet the thermodynamic requirements for water oxidation [26], but of course, other properties such as the mobility of the excited carriers and the presence of active surface sites are also critical to visible-light photocatalysis [20].…”

Polymorphism and Structural Distortions of Mixed-Metal Oxide Photocatalysts Constructed with α-U3O8 Types of Layers

“…Improved charge separation and photocatalytic/photoelectrochemical redox reactions have been proposed to be enhanced in these structures due to the preferential anisotropic diffusion of charge carriers along the BO 7 pentagonal bipyramid layers. The anisotropic charge diffusion is a result of the delocalization of the Nb 4d and the Ta 5d lowest-energy unoccupied crystal orbitals across the BO 7 pentagonal bipyramid layers, as confirmed by electronic structure calculations which show the largest band dispersion in these crystallographic directions [35,47,64,65,71,[122][123][124][125][126][127][128].…”

Structural and electronic investigations of PbTa4O11 and BiTa7O19 constructed from α-U3O8 types of layers

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Structures in this family are based on the stacking of Į-U 3 O 8 type of pentagonal bipyramidal NbO 7 or TaO 7 layers, where n defines the average thickness (1 2 n ≤ ≤ ) of the BO 7 layers. [1][2][3][4][5][6][7][8][9][10]13,16,18,19,22 The many previously reported ternary phases are a result of the diverse range of A-site metal cations (e.g., Na, Ag, Cu, Pb, La, Bi, Ce, etc.) that occupy the interlayer sites, which includes 2-, 6-, 7-, and 8-coordinate sites.…”