Progress in Solid State Chemistry最新文献

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.

The series $R{T}_2{X}_8$ (R = La–Nd, Sm, Eu, Yb, Ca and Sr; T = Fe, Co, Ni, Ru, Rh and Ir; X = Al, Ga and In) belong to a class of quasi-skutterudite intermetallic compounds which crystallize in the orthorhombic CaCo₂Al₈-type structure with space group $Pbam$ (No. 55). A new member of the series CePd₂Al₈ crystallizes in a monoclinic structure of its own type with space group C2/m (No. 12). While this family of compounds are still largely unexplored, recent studies have revealed the evolution of interesting electronic and magnetic ground states in certain members of the series. Due to an increasing interest in the study of compounds with cage-like structures owing to their promising properties for thermoelectric applications and the search for heavy fermion superconductivity, it is therefore imperative to put into perspective the observations and important results in previous studies on the $R{T}_2{X}_8$ series. Besides the macroscopic properties such as specific heat, transport properties and magnetization, other important results from techniques such as neutron scattering, X-ray absorption spectroscopy and Mössbauer spectroscopy are also presented for some of the compounds.

Environmental pollution is one of the significant area under discussion that the world is facing nowadays and it is increasing day by day and leading to serious and dangerous consequence to this world. Electrical energy storage (EES) plays a very important part in everyday life because of our reliance on various transportable devices. Nano- and atomic-level two-dimensional (2D) materials have broad applications in optoelectronic devices. This review deals with the cutting edge of EES devices, highlights advances to overcome present restrictions, and helps us to go further to get future advanced EES technology based devices, whose uniqueness symbolizes an exact hybridization of batteries and capacitors. The essential features of 2D materials are illustrated, and their energy storage systems are also reviewed. Secondly, energy storage performances of 2D materials-based batteries and supercapacitors (SC) will also be highlighted. At last, a few efficient schemes for boosting their performance based on 2D materials are also explained. The prospect and challenges of the 2D-material-based energy storage at commercial level are also provided.

The photoluminescent phosphor materials nowadays are extremely important source of light to fulfill the technological demand over the conventional light source for eco-friendly environment. This review brings the morphological and optical properties of the chemically engineered rare earth doped photoluminescent materials at one platform. The recent developments have been incorporated and different processes involved in the morphological changes of these materials are discussed. The optical properties of different mono-, di- and tri-rare earth doped phosphors have been analyzed and evaluated using various sensitizers and surface modifiers. The photoluminescence intensity of the materials is greatly affected by changing the morphology of the phosphors via some sensitizers and surface modifiers. The large photoluminescence intensity thus obtained has been summarized due to change in the morphology. The future aspects of change in the morphological properties of the chemically engineered rare earth doped phosphors have been also proposed.