Progress in Solid State Chemistry最新文献

Thermodynamic properties and structural aspects of the nonstoichiometric wüstite Fe_1-zO, and its modifications - the so-called pseudo-phases - as functions of departure z from stoichiometry and of equilibrium temperature are reviewed from 1960 to present. The complexity of the equilibrium phase diagram is described in some details. The first order transition W ⇆ W′ is specified on the iron/wüstite boundary near 1185 K. Transitions correlated to the modifications Wi at T(W) > 1185 K and W'j at T(W′) < 1185 K (i and j = 1,2,3) are re-examined. Structural determinations based on the characterization of point defects stabilization and of their clustering are reviewed. Additionally, the pseudo-phases are examined based on the transformation of defect clusters or of their mode of distribution (i.e., percolation or superstructure) with the inclusion of changes in electronic charge carriers.

Intermetallic compounds (IMCs) exhibits unique structural features accompanied by appropriate changes in the electronic structures. These electronically and geometrically tuned structures found to be the excellent catalysts for selected chemical reactions. There is not enough literature comprising detailed synthesis, properties and catalytic activity of IMCs. In this review, a complete overview of the IMCs in the field of heterogeneous catalysis has been discussed in detail. The review starts with understanding IMCs and how are they different from alloys, solid solutions and bimetallic. The physicochemical properties such as electronic effect, geometrical effect, steric effect and ordering of the IMCs are explained with appropriate examples. The comprehensive discussion on the synthesis and characterization of IMCs by various methods are also included in the review. The review cover the classification of IMCs into mainly 3 groups based on the active metal a) Platinum b) Palladium c) Nickel and the compounds based on each of these family is discussed along with the structure-activity correlation in different organic reactions. Several miscellaneous examples including other active metals Rh, Ru, Al, and Co are also included in the review followed by the future perspective. Overall, one can fine-tune and design the essential electronic -geometrical properties in the IMCs by combining appropriate metals, leading to the new surface properties suitable for the important organic reactions.

Reduction of CO₂ using a heterogeneous photocatalyst under visible light has been studied as a potential means to address the problems of global warming and the depletion of fossil fuels. Recently, hybrid photocatalysts constructed with a metal complex and a particulate semiconductor are of particular interest because of the excellent electrochemical (and/or photocatalytic) ability of the metal complexes for CO₂ reduction and the high efficiency of the semiconductors for oxidation reactions, where the ultimate target of oxidation reaction is water oxidation to form molecular O₂. This review article highlights our recent progress in the development of metal-complex/semiconductor hybrid materials for visible-light CO₂ reduction with a focus on oxynitride and nitride materials as the semiconductor component.

Compounds that contain two types of anion are attracting attention as a new field of solid state chemistry. The nitride anion is similar to the oxide anion in size and nature. They coordinate together to cations in oxynitrides to form characteristic local structures around them in a certain way. Special properties induced by the specific local structure have been observed in oxynitrides. Ferroelectricity was identified in oxynitride perovskites, especially those of tantalum, because the oxide and nitride anions form a polar ordered local crystal structure around Ta⁵⁺ in the 5d⁰ electron configuration. The critical current density in superconductivity was enhanced by the formation of clusters in niobium oxynitrides with the rocksalt-type structure. Main group elements doped into the niobium oxynitrides, especially silicon, are coordinated mainly by oxides with some amount of nitrides to form silicon oxide-like clusters. The niobium in the oxynitride has some 4d electrons to maintain the superconductivity in the niobium oxynitride host. Here, the preparation, crystal structure and properties of oxynitrides formed with tantalum and niobium are reviewed.

Recent advances in the chemistry of two peculiar nitrogen-based materials, that is, ternary itinerant iron nitrides and unsubstituted guanidinate salts, are reviewed. Key to their synthesis is the versatile tool ammonia, either as a gas or as a liquid. For metallic nitrides M_xFe_4−xN including transition-metal and main-group elements M, it is of paramount importance to follow an improved ammonolytic reaction for achieving both stable and metastable compounds; in addition, there is a magnetic effect acting on the crystal structure of Ga_xFe_4−xN, and one also finds spin-glass behavior in main-group nitrides (M = Ga, Ge, Sn). The guanidinate review features an oxidation-controlled low-temperature synthesis of Yb salts, the first magnetic guanidinates, and the doubly-deprotonated guanidinates; the latter represent the all-nitrogen analogues of the ubiquitous carbonates. The covered guanidinates adopt the compositions MCN₃H₄, M(CN₃H₄)₂, M(CN₃H₄)₃ and MC(NH)₃ (M = Li–Cs, Sr, Eu, Yb). We also cover the application of first-principles calculations at all levels to gain a deeper understanding of the studied materials.

Si,Al containing nitride and oxynitride phosphors have been applied to white LEDs. Phosphors play important roles to produce high color rendering in lighting and wide color gamut in display. Si,Al containing nitrides and oxynitrides have been studied as high-temperature materials with high strength and thermal shock resistance. The inherited high temperature property is utilized as low thermal quenching in luminescence. The increased covalent bonding character compared to oxide phosphors contributes to high efficiency in blue excitation. The crystal structure (especially the coordination sphere around luminescent center) dominates the luminescent property of phosphor. Wide variety of crystal structure in Si,Al containing nitride and oxynitride leads to multiplicity of luminescent property. In this contribution, Si,Al containing nitride and oxynitride phosphors are reviewed from viewpoints of synthesis, new phosphor discovery, and crystal structure.

Strong ferromagnetic materials at room temperature are of interest for various magnetic applications such as magnetic recording, sensors, and motors. Gigantic magnetism expected for α″-Fe₁₆N₂ thin films had been attracted much attention in terms of its large magnetization per weight in comparison to rare earth iron nitrides R₂Fe₁₇N₃ because these films are made of only iron and nitrogen. It developed much straggling on iron nitride thin film research but inconsistent results were obtained using different preparation methods. A powdered α″-Fe₁₆N₂-like compound was prepared by the ammonolysis of fine α-Fe powder in low temperature below 200 °C to clarify the confusion; the magnetism was not large in α″-Fe₁₆N₂ itself but was increased in the intermediate ammonolysis dual-phase mixture product of the α″-Fe₁₆N₂-like compound and residual α-Fe. A way to control the magnetic coercivity was subsequently investigated to utilize the larger magnetization in the α″-Fe₁₆N₂-like compound mixture as magnetic materials similarly to Sm₂Fe₁₇N₃ bonded magnet. Iron nitrides, zinc blende type γ″-FeN and rock-salt type γ‴-FeN, also decompose at around 500 °C. Thermal decomposition was a disadvantage in the preparation of the iron nitrides; however, iron nanoparticles dispersed composites in AlN matrix were derived from the iron nitrides (Fe,Al)N by thermal treatment including laser heating. Iron nitrides are thus promising magnetic materials for their potential applications in science and technology.

Mixed anion oxides are emerging materials showing a variety of physical and chemical properties. Among them oxynitrides are widely investigated because of notable photocatalytic, dielectric, luminescent and electronic properties. Nitrides show more positive free energies of formation than oxides because of the higher stability of N₂ molecule with respect to O₂ and the unfavourable electron affinity of nitrogen compared to oxygen. However the stability of oxynitrides is higher than for nitrides, and they easily form from oxides in presence of reactive gases as NH₃. In addition to ammonolysis several synthetic strategies have been developed in the last years leading to the stabilization of relevant materials with a variety of structures. In this review we will discuss recent progress in the synthesis of oxynitrides emphasizing the importance of kinetic factors and the influence of preparative parameters on the structure types and oxidation states of the cations, and the consequences on physical properties.

Studies of the synthesis of solid state nitrides using a Na flux are reviewed. The role and effect of Na is to solubilize polyatomic species containing nitrogen, and to lower the crystal growth temperature below the decomposition temperature of the obtained product(s). Many new ternary and quaternary nitrides have been synthesized in single crystal forms with sizes at least large enough (or larger) than is needed for structure analysis by X-ray diffraction. Isolated and extended anionic groups typically containing N and Si, Ge, Ga, and/or some transition metal elements are typical. These are usually surrounded by alkaline-earth atoms and are the most common of such nitrides. Compounds composed of nitridometallate anions and Zintl polyanions are also obtained. The structural features of each of these compounds are described.

Transition metal nitride and carbide have several similarities in their preparatory methods, properties, and applications. Synthetic parameters have remained the main factors that determine the effectiveness of nitrides and carbides in electrochemical storage devices, photocatalysis, environmental remediation, gas sensing and medicinal agents. This review addresses aspects of relevance to electronic structure and chemical bonding, and recent advances made in the synthesis approaches. The syntheses approaches that are particularly relevant for reducing (i) production cost, (ii) energy consumption, and (iii) synthesis time for these materials systems are discussed in detail. Furthermore some of the recent techniques like solid-solid state separation, carbothermal, gas-phase, electrochemical, sonochemical, solvothermal, sol-gel reaction and solid state reaction that offer new avenues for researchers (including a sustainability-oriented exploration) are mentioned. We discuss synthetically tunable properties (morphology, electronic characteristics, energy storage capacity, corrosion resistance, catalytic ability and gas sensing properties), heat treatment aspects, and relevant applications of these systems. We expect this review to be useful to the ever growing community of researchers that are interested in nitrides and carbides, and their applications.