Two-dimensional materials do not only attract interest owing to their anisotropic properties and quantum confinement effects but also lend themselves as well-defined building blocks for the rational design of 3D materials with custom-made structures and, hence, properties. Here, we present the bottom-up fabrication of an artificial superlattice derived from positively charged layered double hydroxide (LDH) and negatively charged perovskite layers sequentially assembled by electrostatic layer-by-layer deposition. In contrast to previously employed bulk methods averaging out the elemental distribution within such stacks, we use a combination of HRTEM, STEM, and EEL spectroscopy to elucidate the structure and composition of the multilayer stack with a high spatial resolution on the subnanometer scale. Atomic column resolved STEM coupled with EELS line scans confirms the periodic arrangement of individual nanosheets by evaluation of the Ca-L 2,3 and Mn-L 2,3 edges. Furthermore, HRTEM confirms the formation of up to 100 double layer thick films, thus demonstrating the transition from ultrathin nanosheet assemblies to artificial bulk solids with engineered structures and property profiles. We ascertain the formation of densely packed stacks with a well-ordered layered morphology, while nonidealities such as lack of in-plane layer registry, layer terminations, sheet bending, and contamination by residual ligands are side effects of the solution-based deposition process. In addition, we demonstrate that the packing density of the multilayer system can be tuned by changing the LDH dispersing agent from formamide to water, resulting in porous stacks containing about eight times less LDH and featuring significantly increased interlayer distances.
The subnitridometalates Ba23 Na11 (MN4 )4 (M=V, Nb, Ta) crystallize in a new structure type, which shows ionic ortho-nitridometalate anions and motifs from simple (inter)metallic packings: Na-centered [Na8 ] cubes as cutouts of the bcc structure of elemental Na and Na-centered [Ba10 Na2 ] icosahedra as found in Laves phases, for example. Single-crystal and powder X-ray diffraction studies in combination with quantum-chemical calculations of the electronic structure and Raman spectroscopy support the characterization of the subnitridometalates as "chemical twins". They consist of independent building units with locally prevalent ionic or metallic bonding in an overall metallic compound.
The crystal structures of the new cesium-poor alkali metal suboxometalates Cs10MO5 (M = Al, Ga, Fe) show both metallic and ionic bonding following the formal description (Cs(+))10(MO4(5-))(O(2-))·3e(-). Comparable to the cesium-rich suboxometalates Cs9MO4 (M = Al, Ga, In, Fe, Sc) with ionic subdivision (Cs(+))9(MO4(5-))·4e(-), they contain an oxometalate anion [M(III)O4](5-) embedded in a metallic matrix of cesium atoms. Columnlike building units form with prevalent ionic bonding inside and metallic bonding on the outer surface. In the cesium-rich suboxometalates Cs9MO4, additional cesium atoms with no contact to any anion are inserted between columns of the formal composition [Cs8MO4]. In the cesium-poor suboxometalates Cs10MO5, the same columns are extended by face-sharing [Cs6O] units, and no additional cesium atoms are present. The terms "cesium-rich" and "cesium-poor" here refer to the Cs:O ratio. The new suboxometalates Cs10MO5 crystallize in two modifications with new structure types. The orthorhombic modification adopts a structure with four formula units per unit cell in space group Pnnm with a = 11.158(3) Å, b = 23.693(15) Å, and c = 12.229(3) Å for Cs10AlO5. The monoclinic modification crystallizes with eight formula units per unit cell in space group C2/c with a = 21.195(3) Å, b = 12.480(1) Å, c = 24.120(4) Å, and β = 98.06(1)° for Cs10AlO5. Limits to phase formation are given by the restriction that the M atoms must be trivalent and by geometric size restrictions for the insertion of [Cs6O] blocks in Cs10MO5. All of the suboxometalate structures show similar structural details and form mixed crystal series with statistical occupation for the M elements following the patterns Cs9(M(1)xM(2)1-x)O4 and Cs10(M(1)xM(2)1-x)O5. The suboxometalates are a new example of ordered intergrowth of ionic and metallic structure elements, allowing for the combination of properties related to both ionic and metallic materials.
Die Subnitridometallate Ba23Na11(MN4)4 (M=V, Nb, Ta) kristallisieren in einem neuen Strukturtyp, in dem sowohl ionische ortho‐Nitridometallat‐Anionen als auch Strukturmotive aus einfachen (inter)metallischen Packungen zu finden sind: Na‐zentrierte [Na8]‐Würfel als Ausschnitte aus der bcc‐Struktur von elementarem Natrium und Na‐zentrierte [Ba10Na2]‐Ikosaeder, wie sie z. B. in Laves‐Phasen vorkommen. Einkristall‐ und Pulverröntgenstrukturanalyse unterstreichen in Kombination mit quantenchemischen Berechnungen der elektronischen Struktur und Raman‐Spektroskopie den Charakter der Subnitridometallate als “chemische Zwillinge”. Sie weisen unabhängige Strukturbausteine mit lokal überwiegend entweder ionischer oder metallischer Bindung in einer insgesamt metallischen Verbindung auf.
The subvalent nitridometalate Ba 6 [(Mo 1-x Ta x )N 4 ]N 0.86 was prepared from mixtures of Mo powder with Ba, Na, and Ba 2 N at 600°C in Ta ampoules. It crystallizes in space group Cmcm with a = 11.672(3), b = 10.177(2) and c = 10.8729(19) Å. Its crystal structure exhibits an orthorhombically distorted Perovskite topology with [Ba 6 N] building units forming the ReO 3 -type lattice via common vertices, and the nitridometalate anions occupying half of the available distorted cuboctahedral interstices. [MN 4 ] anions show statistically
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.