Abstract
A series of mixed-metal oxide structures based on the stacking of α-U3O8 type pentagonal bipyramid layers have been investigated for symmetry lowering distortions and photocatalytic activity. The family of structures contains the general composition Am+((n+1)/m)B(3n+1)O(8n+3) (e.g., A = Ag, Bi, Ca, Cu, Ce, Dy, Eu, Gd K, La, Nd, Pb, Pr, Sr, Y; B = Nb, Ta; m = 1–3; n = 1, 1.5, 2), and the edge-shared BO7 pentagonal pyramid single, double, and/or triple layers are differentiated by the average thickness, (i.e., 1 ≤ n ≤ 2), of the BO7 layers and the local coordination environment of the “A” site cations. Temperature dependent polymorphism has been investigated for structures containing single layered (n = 1) monovalent (m = 1) “A” site cations (e.g., Ag2Nb4O11, Na2Nb4O11, and Cu2Ta4O11). Furthermore, symmetry lowering distortions were observed for the Pb ion-exchange synthesis of Ag2Ta4O11 to yield PbTa4O11. Several members within the subset of the family have been constructed with optical and electronic properties that are suitable for the conversion of solar energy to chemical fuels via water splitting.
Highlights
Many properties and applications of inorganic materials are derived from a small number of reported structure types
The crystal structure of U3 O8 was first proposed by Zachariasen [27], further investigations of the single crystal and neutron diffraction confirmed the orthorhombic crystal structure of U3 O8 [28,29,30]
Symmetry-lowering structural distortions have been reported for the monovalent A-site niobate cations Na and Ag, as well as the monovalent “A”site Cu cation in the tantalate structures, which will be further discussed in a separate section of this review
Summary
Many properties and applications of inorganic materials are derived from a small number of reported structure types. A polysomatic family of structures with the general orthorhombic unit cell toB a hexagonal unit cell at ≈210 °C [32,33,34]. Synthesis and structural investigations of these systems of mixed six-, seven-, and eight-coordination sites [35]. Several of the display symmetry lowering distortions, and unique optical and electronic properties that are viable for structures in the system display symmetry lowering distortions, and unique optical and electronic the direct conversion of solar energy into chemical fuels. This edge-shared pentagonal bipyramid layer is the principle building block block for a polysomatic of structures with the general composition. Single and layers triple layers of edge-shared pentagonal bipyramid polyhedra. Alternate with and triple of edge-shared pentagonal bipyramid polyhedra These These layers layers alternate with layers layers of isolated octahedra along the (001) direction.
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