CuSe-based layered compoundBi2YO4Cu2Se2as a quasi-two-d

Abstract

We have investigated the physical properties of a new layered oxyselenide Bi2YO4Cu2Se2, which crystallizes in an unusual intergrowth structure with Cu 2 Se 2 and Bi2YO4 layers. Electric transport measurement indicates that Bi2YO4Cu2Se2 behaves metallic. Thermal transport and Hall measurements show that the type of the carriers is hole-like and it may be a potential thermoelectric material at high temperatures. First principle calculations are in agreement with experimental results and show that Bi2YO4Cu2Se2 is a quasi-2D metal. Further theoretical investigation suggests the ground states of the Bi2YO4Cu2Se2-type can be tuned by designing the blocking layers, which will enrich the physical properties of these compounds.

Semiconducting BiOCuSe Thermoelectrics and Its Metallic Derivative Bi2YO4Cu2Se2

“…However, even though crystallography-wise these two layered materials can be described as natural superlattices, they present parabolic density of states (DOS) as a classical three-dimensional (3D) system rather than step-like ones. [14][15][16] The two phases, BiOCuSe and Bi 2 YO 4 Cu 2 Se 2 , present sharply different temperature dependencies of electrical properties (see Figure 2). The resistivity (ρ) of BiOCuSe first decreases with decreasing temperature and then rises below ca.…”

“…In BiOCuSe, the oxide and selenide blocks consist of edge-shared OBi 4 [14] already concluded that the valence band maximum (VBM) of Bi 2 YO 4 Cu 2 Se 2 is composed of hybridized Cu (d xy + d yz ) and Se (p x + p y ) states but negligible Se p z contribution to the interlayer conduction. However, even though crystallography-wise these two layered materials can be described as natural superlattices, they present parabolic density of states (DOS) as a classical three-dimensional (3D) system rather than step-like ones.…”

“…[20] Let us then discuss the local structures of the Cu-Se blocks in BiOCuSe and Bi 2 YO 4 in the mixed Cu + /Cu 2+ valence state. Experimentally, Tan et al [14] found Cu 2+ but no evidence of magnetic ordering at low temperature in their electron paramagnetic resonance (EPR) analysis; note that nonmagnetic Cu + is not visible in EPR. Looking at our Cu-K edge XANES spectra shown in Figure 3(c), the most evident feature in common for both BiOCuSe and Bi 2 YO 4 Cu 2 Se 2 and also the Cu 2 Se reference is the edge profile typical for Cu + in a tetrahedral coordination.…”

“…536 eV in the spectrum of Bi 2 YO 4 Cu 2 Se 2 stem from the O 2p -Bi 6p and O 2p -Y 4d hybridizations, respectively. [14,19] The higher intensity of the white lines (after normalizing) at both Bi and O edges of Bi 2 YO 4 Cu 2 Se 2 reveals more hole states due to the augmented covalent character in the metal oxide block layer. [20] Let us then discuss the local structures of the Cu-Se blocks in BiOCuSe and Bi 2 YO 4 in the mixed Cu + /Cu 2+ valence state.…”

“…At room temperature the Bi 2 YO 4 Cu 2 Se 2 phase moreover shows rather low κ (5 W/ m K) and decent S (25 μV/K) in its metallic ground state. [14] We foresee that the Bi 2 YO 4 Cu 2 Se 2 -type intergrowth phases could constitute a novel family of high-performance thermoelectric materials once we can optimize the carrier doping so as to simultaneously achieve reasonably high σ and S values either by (partially) replacing the trivalent cations with tetravalent ones or replacing O 2-with F -in the oxide blocks. Here we report our comprehensive X-ray absorption spectroscopy study at different absorption edges for the local electronic structures of the two existing layered oxyselenides, BiOCuSe and Bi 2 YO 4 Cu 2 Se 2 , and experimentally affirm where the marked difference in their electrical …”