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Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure



Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure

Creation of ZnSb in 2D layers. (A) Schematic illustration of the dimensional manipulation of a crystal structure from 3D-ZnSb to 2D-ZnSb via Li alloying and etching processes. The Li alloy in 3D-ZnSb has was performed by thermal and electrochemical (ER) reactions. Selective etching of Li ions was carried out by reaction with a reaction in polar solvent solution (SR). A reversible process of alloying and etching occurs during the electrochemical reaction (ER). (B) XRD models of 3D-ZnSb and 2D-LiZnSb. The polycrystal and the single crystal of 2D-LiZnSb were synthesized using 3D-ZnSb synthesized as a precursor. All models correspond well to the simulated models of the corresponding compounds. a.u., arbitrary units. (C) X-ray diffraction patterns of 2D-ZnSb crystals obtained by solution reaction and electrochemical reaction processes. For the reaction process in solution, water-based solutions [DI water and dimethyl sulfoxide (DMSO) with 1 volume % of DI water, and hexamethyl phosphoric triamide (HMPA) with 1 volume % of DI water] were used. For the electrochemical reaction process, 1M LiPF6 dissolved in a 1: 1 mixture of ethylene carbonate and a solution of diethyl carbonate was used as the electrolyte. The distances between the layers were calculated from the highest intensity angle. (D to I) Scanning electron microscopy (D to F) and optical images (G to I) of 2D-LiZnSb and 2D-ZnSb created by solution reaction and electrochemical reaction processes. The 2D-ZnSb flakes were exfoliated by mechanical splitting with the aid of a 3M band. (J to L) X-ray photoelectron spectroscopy (XPS) of the spectra of Li 1s (J), Zn 2p (K) and Sb 3d (L) for 3D-ZnSb, 2D-LiZnSb and 2D-ZnSb, respectively . The peak of Li 1s (54.6 eV) of 2D-LiZnSb indicates the state Li1 +. While the binding energies of Zn 2p3 / 2 (1019.8 eV) and Sb 3d5 / 2 (525.8 eV) are significantly lower than those of Zn 2p3 / 2 (1021.5 eV) and Sb 3d5 / 2 (527.6 eV) in 3D-ZnSb, the binding energies of Zn 2p3 / 2 (1022.1 eV) and Sb 3d5 / 2 (528.2 eV) of 2D-ZnSb are slightly higher than those of 3D -ZnSb. Credit: Science Advances, doi: 10.1126 / sciadv.aax0390

The discovery of new families of two-dimensional (2D) materials beyond graphene has always attracted attention, but the artificial restitution of the atomic honeycomb network structure with multiple components such as hexagonal boron nitride remains difficult. In a new study now published on Progress of scienceJunseong Song and colleagues from the Departments of Energy Science, Nanostructural Physics, Environmental Science and Materials in the Republic of Korea have developed an unprecedented Zintl phase structure.

They built the material by staking sp2Hybrid honeycomb ZnSb layers and by the dimensional manipulation of a crystalline structure3-hybrid 3-D-ZnSb. Material scientists have combined structural analysis with theoretical calculations to form a stable and robust layered structure of 2-D-ZnSb. This phenomenon of two-dimensional polymorphism was not previously observed at ambient pressure in the Zintl families. Therefore, the new work provides a rational design strategy for searching and creating new 2D layered materials in various compounds. The new results will allow unlimited expansion of 2D libraries and their corresponding physical properties.

The advent of graphene physics by Dirac has sparked an explosive interest in two-dimensional (2D) materials research with diverse applications in electronics, magnetism, energy, and chemistry in quantum physics. At present, the 2D research focuses mainly on a few 2D materials containing one or more exfoliated atomic layers of their parent compounds, as opposed to 2D atomic crystals such as silicone. This can limit the method of developing 2D materials to two approaches to exfoliation and chemical vapor deposition. It is therefore highly desirable to develop research on 2D materials in order to artificially create a new 2D material with a new synthesis approach and to form a variety of material groups.

In the discovery of new materials, the transformation of a crystalline structure is a widely recognized key factor. Structural phase transitions induced by temperature, pressure and electrostatic doping are essential for exploring a new crystalline structure or for modifying the properties of 2D materials. For example, most transition metal dichalcogenides exhibit a polymorphic phase transition that provides access to inherently diverse properties, including superconducting and topological states. The transition has led to promising applications, including electronic homo junction, photonic memory devices and catalytic energy materials.

Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure

Crystal structure of ZnSb in 2D layers. (A and B) Images in resolution STEM-HAADF (high angle annular dark field) of 2D-LiZnSb resolution along the [110] (A) and [001] (B) zone axes, respectively. (C) STEM-EDS elementary mapping in atomic resolution for 2D-LiZnSb along the [110] (top) and [001] axes of the zone (bottom). (D and E) STEM-HAADF atomic resolution 2D-ZnSb images along the [110] (D) and [211] (E) zone axes. The determined crystalline structure of 2D-ZnSb. The atomic distances of 2D-ZnSb are compared with those of 3D-ZnSb and 2D-LiZnSb. From observation to [211] 2D-ZnSb area axis, the honeycomb network is slightly inclined. For lithium detection, the STEM-EELS technique (electron energy loss spectroscopy) was used, showing the clear existence and absence of lithium in 2D-LiZnSb and 2D-ZnSb. (G) Calculation of cohesion energy (ΔEcoh) of predictable 2D-ZnSb structures. Structure I, which is determined from the STEM observations, has the lowest energy compared to the other candidates, showing an excellent agreement between experiments and calculations. Credit: Science Advances, doi: 10.1126 / sciadv.aax0390

These polymorphic transitions occurred only between different layered structures in the same two dimensions and remain to be achieved between different dimensions of a crystalline structure at ambient pressure. Achieving the ultimate crystalline engineering and changing the structural dimension of multicomponent compounds is a promising new frontier in the science of materials beyond carbon allotropes.

In this work, Song et al. Two-dimensional polymorphism established via the discovery of two-dimensional layer structures in Zintl phases containing a large number of chemical compositions. Because of the sp2 Hybrid orbital bonding of honeycomb structured 2D atomic crystals such as graphene and hexagonal boron nitride, scientists expected to 3D-structured Zintl phases (with3 hybrid orbital link) to transform into sp2 2-D structured honeycomb layered materials, also, by electron transfer. As proof of concept, Song et al. selected a 3-D orthorhombic ZintS ZnSb (3-D-ZnSb) phase and created the unprecedented two-dimensional ZnSb layer structure (2-D-ZnSb).

In the new method, Song et al. the first ternary compounds in AZnSb (2-D-AZnSb) in synthesized layers; A relates to an alkali metal such as Na, Li and K. The materials contain a ZnSb layered structure by transformation of 3-D-ZnSb via an alloy A, although the phases can be synthesized independently. Song et al. performed selective etching of A-ions to create 2-D-ZnSb in two different processes, including (1) a chemical reaction in solutions containing demineralized water, and (2) an electrochemical ion etching reaction in an electrolyte based on alkali.

Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure

Electronic properties of ZnSb in 2D layers. (A to C) Dependence of electrical resistivity (A), Hall mobility (B) and carrier concentration (C) as a function of temperature for 3D-ZnSb, 2D-LiZnSb and 2D-ZnSb models . The two-dimensional polymorphs of 3D-ZnSb and 2D-ZnSb show the metal-insulator transition. (D to F) 3D-ZnSb (D), 2D-LiZnSb (E) and 2D-ZnSb (F) electronic band structures. The 3D-ZnSb (D) and 2D-LiZnSb (E) band structures indicate that both are semiconductors with a well-defined indirect band gap of 0.05 and 0.29 eV, respectively. Low electrical resistivity and a high concentration of 2D-LiZnSb carriers indicate strongly doped semiconductor behavior. Credit: Science Advances, doi: 10.1126 / sciadv.aax0390

For example, they synthesized the polycrystalline and monocrystalline intermediate 2-D-LiZnSb substrate by first combining Li into polycrystalline 3-D-ZnSb followed by ionic etching to form a 2-D crystal. -ZnSb. Scientists easily cleaned Li-etched 2-D-ZnSb crystals using adhesive tape exfoliation as a mechanical split to present a flat surface typical of two-dimensional materials.

To understand the effect of the manufacturing process, they examined the role of Li alloying and etching on structural transformations using X-ray photoelectron spectroscopy (XPS) measurements. to reveal the difference between two-dimensional and three-dimensional crystals. To further validate their conclusions, Song et al. X-ray diffraction spectroscopy (XRD) models used, transmission electron microscopy (TEM) and tunneling tunneling electron microscopy (STEM) observations, combined with elemental energy dispersive spectroscopy mapping ( EDS) to confirm the atomic structure of 2-D-ZnSb.

On the basis of the results, the scientists interpreted the interlayer stretchable distances between the Zn-Zn and Sb-Sb atoms as weak inter-layer bonds and verified that 2-D-ZnSb could be exfoliated in the form of of laminated material. The newly developed layered structure of 2-D-ZnSb in the present work completed the first discovery of two-dimensional polymorphism in Zintl phases at ambient pressure.

Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure

2D layered behavior of 2D-ZnSb. (A) [100] view of 3D-ZnSb. (B) [100] view of 2D-ZnSb. (C) Calculation of cohesion energy (ΔEcoh) of 3D-ZnSb, 2D-ZnSb. From the calculation of the cohesion energy, the 3D-ZnSb is more stable, but the cohesion energy of the 2D-ZnSb is sufficiently large, indicating that the 2D-ZnSb exists as a stable material. (D) The calculation of Li alloy energy (ΔELi alloy) of 3D-ZnSb and 2D-ZnSb indicating the reaction of the Li alloy process in 2D-ZnSb and 3D-ZnSb is an energetic favor. Compare two alloys ΔELi allies, Li binding 2D-ZnSb is more favorable than 3D-ZnSb. (E) Interlayer bonding energy (Einter) of 3D-ZnSb and 2D-ZnSb. A big difference Einter between 3D-ZnSb and 2DZnSb indicates the characteristics of 2D layered materials for 2D-ZnSb. (F) Calculation of exfoliation energy (Eexf) of 2D-ZnSb and other 2D materials. Eexf of 2D-ZnSb is rather superior to that of conventional van der Waals (vdW) related 2D materials such as graphene and h-BN, indicating that 2D-ZnSb is not a layered material of type vdW. However, the 2D-ZnSb Eexf is lower than that of the antimonene, which can be exfoliated or grown in monolayer, indicating that an autonomous monolayer or some 2D ZnSb layers may be possible as standard 2D vdW layer materials. Credit: Science Advances, doi: 10.1126 / sciadv.aax0390.

As a result, Song et al. handled the sp3-hybridized binding state in 3-D-ZnSb in the sp2 state in the honeycomb network 2-D-ZnSb. Previous studies on polymorphic transitions between 3D and 2D structures in Zintl phases have only been observed under high pressure. The present results on the two-dimensional polymorphism between 3-D-ZnSb and 2-D-ZnSb have highlighted the potential and wide availability of such an electron transfer to transform the crystal structure.

Song et al. We then studied the electrical transport properties of two-dimensional ZnSb polymorphs and 2-D-LiZnSb crystals, as well as calculations according to the basic principles of their electronic energy band structure. In contrast to the semiconductor nature of 3-D-ZnSb, 2-D-LiZnSb and 2-D-ZnSb both exhibited metallic conduction behavior. When they decreased the temperature, the electrical mobilities of 2-D-LiZnSb and 2-D-ZnSb increased to a higher value than 3-D-ZnSb. Scientists have attributed the increase in observed bandwidths for 2-D-ZnSb2 nature of structured honeycomb layers with weak interactions between the layers that formed the semi-metal. They used theoretical calculations to confirm that 2-D-ZnSb could be exfoliated mechanically in the bilayer to exist in an energetically stable form as a 2-D material, whereas the 2-D-ZnSb monolayer was energetically unfavorable .

Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystalline structure

Dimensional manipulation of a crystalline structure for the two-dimensional polymorphic ZnSb. (A and B) In situ synchrotron powder XRD diagrams using 3D-ZnSb (A) and 2D-ZnSb (B) via the electrochemical reaction. The alloying and attacking processes were controlled by reducing and increasing the voltage potential, respectively. The inset (bottom left) of (A) shows the peak offset of the (002) plane for 3D-ZnSb. The inset (top left) of (A) shows the disappearance of the peaks corresponding to the diffraction peaks (002) and (101) at 11.1 ° and 11.7 ° of Li-2 DSb 2D with Li, which indicates the transformation into 2D-ZnSb. The inset (middle) shows the appearance and disappearance of byproduct Li1 + xZnSb with discharge and charge reactions, respectively. The incrustations of (B) show the same changes as those observed in the inlays (top left and center) of (A). No diffraction peak of 3D-ZnSb was observed during the reversible structural transformation by Li alloying and etching processes. (C) Schematic illustration of the dimensional manipulation of a structure crystalline, as well as the transition of hybrid sp3 binding characters from 3D-ZnSb to sp2 of 2D-LiZnSb and 2D-ZnSb. The displacement of the fifth Sb blue arrow to the fourth Zn orbital describes the covalent bonding character between Zn and Sb in the honeycomb network. The transfer of electrons from Li-sp3 to the hybrid state of 3D-ZnSb allows the transition to the hybrid sp2 state of the ZnSb honeycomb lattice in 2D-LiZnSb and in 2D-ZnSb. Credit: Science Advances, doi: 10.1126 / sciadv.aax0390.

To demonstrate the structural transformation of two-dimensional ZnSb polymorphs during the formation of 2-D-LiZnSb, the scientists performed a synchrotron XRD – during the electrochemical reaction. They observed peaks corresponding to the 3-D-ZnSb Li alloy to the pure formation of 2-D-LiZnSb, followed by the final product of 2-D-ZnSb. During the electrochemical reaction, the Li atoms selectively penetrated 3-D-ZnSb to break the Zn-Sb and Sb-Sb bonds. At the level of electron transfer, the state of hybrid binding has changed from3 in 3-D-ZnSb with sp2 in 2-D-LiZnSb to form the folded honeycomb network.

The result of the Li-alloy-based 2-D-LiZnSb transformation gave the product 2-D-ZnSb, which did not return to its 3-D form. Song et al. showed that once formed, the layered 2-D-ZnSb was a stable material in honeycomb architecture, validating the stable two-dimensional polymorphic transition. Scientists are anticipating applications of the new material in sustainable alkaline batteries.

Thus, Junseong Song and his collaborators have carried out rigorous experimental and theoretical studies to demonstrate the creation of Zintl phases in 2D layers by manipulating the structural dimensionality. The new method is a first to establish the two-dimensional polymorphic family in the Zintl phases at ambient pressure to allow new phase transformations as a general synthetic route. This work provides a rational design strategy for exploring new two-dimensional layer materials and unlocking other interesting properties, such as 2D magnetism, ferroelectricity, thermoelectricity, and topological states for other applications.


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More information:
Paul F. McMillan. New materials from high pressure experiments, Nature's materials (2003). DOI: 10.1038 / nmat716

Manish Chhowalla et al. The chemistry of transition metal dichalcogenide nanosheets in two-dimensional layers, Nature Chemistry (2013). DOI: 10.1038 / nchem.1589.

Kenneth S. Burch et al. Magnetism in two-dimensional van der Waals materials Nature (2018). DOI: 10.1038 / s41586-018-0631-z

Junseong Song et al. Creation of a two-dimensional layered Zintl phase by dimensional manipulation of the crystal structure, Progress of science (2019). DOI: 10.1126 / sciadv.aax0390

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