Progress in Solid State Chemistry最新文献

Rhombohedral boron (Rh-α) considered as a matrix hosting triatomic linear interstitial elements (E) of the first period (B,C,N,O) and elements of the second period as (Si, P, S) as well as the fourth period (As), generates a relatively large family of solid state chemical systems with B₁₂{E-E-E} generic formulation. This paper was also a good opportunity to make a short review of rh-α boron interstitial compounds. Preliminary energy calculations within quantum density functional theory DFT show enhanced cohesion versus B₁₂ matrix structure upon embedding the {E-E-E} providing compounds with particular physical and chemical properties. Focusing exemplarily on linear {N–C–N} cyanamide known to combine with gallium arsenide giving GaAs:CN₂, as well as in forming calcium cyanamide CaCN₂, the sub carbonitride B₁₂{CN₂} is proposed and studied for its electronic structure. After full unrestricted geometry optimization within B₁₂ space group R$\bar{3}$m and subsequent discussion of the cohesive energies and the energy related properties, details are provided for original electronic and magnetic structures. Particularly we show an elongated N–C–N (d_C-N = 1.38 Å) versus short ones in (ionic) calcium cyanamide CaCN₂ (d_C-N = 1.23 Å) explained by the bonding of N with one of the two B₁₂ boron substructures forming a “3B⋯N–C–N⋯3B “-like complex illustrated by charge density and electron localization function (ELF) and computed from the overlap population (COOP). From energy-volume equation of state EOS in non spin-polarized NSP and spin polarized SP configurations the latter is found to be the ground state one, with a magnetic moment of 2 μ_B carried by central carbon and forming a torus like magnetic charge density. Site and spin projected electronic density of states DOS exhibit a small gap insulator. Furthermore, B₁₂{CN₂} is stabilized due to its magnetic character leading to a strong chemical bonding visualized by the SP COOP. The present conceptual view of B₁₂ as a host of interstitials extends the family of compounds to potential mono- and di-atomic insertions and should enhance research among the communities of solid state chemists and physicist to prepare new compounds with targeted properties.

Energy production highest demand with low-carbon emission is very critical and can be achieved by introducing new low cost but more stable and active electrocatalyst that can improve the efficiency of existing or newly proposed renewable energy devices. Nowadays, oxygen/hydrogen evolution reactions (OER/HER) in water (H₂O) electrolysis is important to cost-efficient formation of pure hydrogen (H₂) fuel, while oxygen reduction reaction (ORR) in fuel cells are experiencing a sluggish reaction kinetics still when load more quantity of precious metals, like benchmark Pt. Therefore, this study is motivated by a requirement to substitute rare precious metal catalysts by nonprecious metals catalysts (NPMCs) two-dimensional materials (2DMs). The 2DMs have a broad significance due to their nano- and atomic-level applications and some of them with prominent electrical properties, which plays very important role in electrocatalytic applications. The NPMCs 2DMs are more efficient than the conventional precious metals based electrocatalysts, as they present flexible electrode configuration, excellent catalytic activity, and high stability, especially in their composite form. In this review we will explain in detail about the 2D based electrocatalysts; those demonstrate high efficiency, selectivity and sustainability for ORR, OER, and HER. The most important point related to electrocatalytic applications of the 2DMs efficiency enhancement is newly introduced confinement effect, and we will mainly concentrate on 2DMs based confinement effect. The diverse ways for modifying electronic states of the 2D confinement electrocatalysts are emphasized and prospects on confinement catalysis by using 2DMs to energy conversion are given. The perspectives on the relevant areas about further enhancement in their properties will also propos and address. Finally, we will discuss in detail about recent progresses made till now and future predictions about the 2DMs in energy producing devices.

Halide based perovskite materials have fascinated strong attention for being a hopeful candidate for optoelectronic device applications. Single-crystalline halide perovskites exhibit no grain boundaries and possess low trap densities; and are therefore likely to show superior optoelectronic performances in comparison to their polycrystalline film counterparts. In spite of this, their basic perceptive of physico-chemical properties are however controversial to the scientific society. In this review article, we present the deep insight into all the reported protocols available for the synthesis of purely inorganic as well as hybrid halide perovskites (incorporating organic as well as inorganic cation) to achieve high-quality single crystals. On account of advanced characteristics like long carrier recombination lifetime and exciton diffusion length, wide-ranging visible to NIR absorption, high charge mobility, controllable optoelectronic properties etc., hybrid halide perovskites have emerged to be a tough challenger in the optoelectronic research area in comparison to the purely inorganic halide perovskites and have consequently been paid much attention. Therefore, the optoelectronic properties and convenient applications of particularly hybrid halide single-crystal perovskites in various optoelectronic devices like solar cell, laser, high energy ray detector, photodetector, light-emitting diode, etc are highlighted.

During the past decade, ab initio electronic structure methods have been extensively developed and employed for properties analysis of perovskites ABO_3–δ, where A is a large cation and B is typically a 3d metal cation of smaller size. The perovskite structure is capable to withstand ample cation substitutions in both A and B sub-lattices and to simultaneously accommodate large amount of oxygen vacancies (δ). The cation and anion defects result in considerable changes in electronic spectrum features and ensuing properties. In the variety of electronic structure calculation methods, the coherent potential approximation (CPA) is a special approach for studies of systems with disordered defects. The method is designed in order to overcome a number of restrictions that arise at employment of supercells such as defect ordering, limitations for defect types and concentrations, a drastic increase in calculation time with defect concentration, etc. The recently developed implementation of the CPA can be used for calculations of electronic spectrum and properties of solid state systems, including strongly correlated ones with an arbitrary concentration, arrangement and type of atomic structural defects. In this brief review, we consider the capabilities and restrictions of classical CPA-combined methods and represent a novel CPA methodology for the case study of electronic spectra and magnetic moments in several perovskite related disordered ferrites including SrFeO_2.5, SrFeO_3−δ and solid solutions La_1−xSr_xFeO_3−δ. These complex oxides with strong electronic correlations attract attention as inexpensive, environmentally friendly and robust materials for applications in high-temperature redox technologies, fuel cells, self-cleaning photocatalysis, water splitting, hydrogen and solar power engineering.

Palladium hydride was discovered more than 150 years ago and remains one of the most-studied interstitial metal hydrides because of the richness of its physical behaviours, which include ordered phases and anomalous properties at temperatures below 100 K, a superabundant-vacancy (SAV) phase with stoichiometry Pd₃H₄ formed at high temperature and pressure, and quenching of the enhanced Pauli paramagnetism of palladium. One of the most fascinating properties of palladium hydride is superconductivity at about 10 K without external pressure, in contrast to the newly-discovered polyhydride room-temperature superconductors that require megabar pressures. Moreover, the superconductivity exhibits an inverse isotope effect. Remarkably, modern first-principles approaches are unable to accurately predict the superconducting transition temperature by calculating the electron–phonon coupling constant within Migdal-Eliashberg theory. Anharmonicity of the hydrogen site potential is a key factor and poses a great challenge, since most theoretical approaches are based on the harmonic approximation. This review focuses on the electron and phonon band structures that underpin all such calculations, with palladium as a reference point. While the electron band structures of palladium and its monohydride are uncontroversial, the phonon band structure of palladium hydride in particular is problematic, with a realistic treatment of anharmonicity required – and largely yet to be achieved – to reproduce the results of inelastic neutron scattering experiments. In addition to the monohydride and SAV phases, possible higher hydrides are surveyed and the origin of the famous “50-K” anomaly in specific heat and other physical properties is critically reviewed.

The innovation of the graphene (G) marks key revolutionary events in the science and technology. The normal materials conversion to the two dimensional materials (2DMs), is known as modern day “alchemy” was extended to the most of groups in periodic table. The monoelemental, atomically thin 2DMs, called “Xenes” (“ene” Latin word, means nanosheets (NSs), here, X = different possible group elements (group-IIIA-IVA)) are newly invented edge of the materials family in which one of the most active area is 2DMs investigation. The 2D-Xenes material offers novel properties for the modern nanodevices applications. Any new form of the 2DMs entry into mainstream Xenes would likely compete with today's electronic technology. The metallic 2D-borophene is experimentally formed; subsequent by the theoretical calculations has high in-plane anisotropy together with numerous enviable features like, the 2D-G and phosphorene (2D-BP). As a synthetic 2DMs, the structural properties of 2D-borophene cannot be deduced from bulk boron (B), means that the fundamental defects of the 2D-borophene persisted unknown. The modern highly sensitive potential synthesis and characterization techniques offer an opportunity for investigating the theoretically predicted 2D-Xenes, with atomic precision under idealized conditions. Experimental based theoretically predicted, synthetic 2D-Xenes of the group-IIIA (Borophene (2D-B)) material has been investigated, just like a metallic material. Thus, it is potentially rendering them as potential candidates for the future electrocatalytic based nanodevices, especially potential applications as a catalyst, electrode material, energy storage materials in batteries/superconductors, and so on. In this topical review, we will briefly present various aspects of the 2D-borophene, group-IIIA 2D-Xenes. Thereafter, we will explain different potential methods to synthesize 2D-borophene Xenes, provide a concise summary of the main achievements about their properties, that have been obtained by theoretical simulations as well as by experimental investigations and finally we will discuss the potential applications of the 2D-borophene Xenes, for fundamentally oriented studies. Although, this material investigations and devices applications are still at an early stage, but theoretical calculations and some experimental measurements, provided that, it is complementary to normally used electrocatalytic nanomaterials as well as 2DMs (i.e., layered bulk-derived), with their novel properties and predicted applications.

Iron-based superconductors are interesting due to their intrinsic magnetism, which often precedes superconductivity. Since 2008, advances have attempted to resolve this apparent but non-obvious link. This has resulted in growing evidence that iron based compounds, especially those containing Fe-X (X = Group15 element) and Fe–Y (Y = Group16 element), have similarities in their superconducting behavior (despite structural dissimilarities). Synthesis of these phases is hence critical in furthering understanding of superconductivity in these systems. Particularly, controlling crystal lattice strain is identified as path towards increasing transition temperature in iron based superconductors. Here highlight factors that are of immediate and future challenges of relevance for these materials. For researchers in these fields, an accessible description of the solid state and structural chemistry of these systems is provided. Phenomena discussed here include (i) spin/orbital fluctuations, (ii) nematicity (iii) vacancy ordering, and (iv) magnetism. These are composition and hence synthesis dependent. Synthetic controls in the case of low dimensional and layered chalcogenide and pnictide superconductors are duly elucidated. It may be noted that just like Fe; X, Y are oftentimes earth abundant elements, making this category of materials prospectively relevant for future applications. We expect pointers provided here to aid multidisciplinary research on iron based superconductors.