Progress in Solid State Chemistry最新文献

Band gap engineering of TiO₂ has attracted many researchers looking to extend its applicability as a functional material. Although TiO₂ has been commercialised in applications that utilise its special properties, its band gap should be modified to improve its performance, especially as an active photo catalyst. Reduction of TiO₂ under a hydrogen atmosphere is a promising method which can increase the visible-light absorption efficiency of TiO₂ and enhance its electrochemical and other properties related to electronic band structure. In this second review paper, the production and influence of O vacancies $\left(V_O\right)$ and other defects, such as interstitial cations, under vacuum and hydrogen are reviewed for the common phases of TiO₂. The particular modification TiO_2–x in which O is randomly removed from the crystal structure is considered in detail. Despite early evidence that hydrogen is absorbed into the bulk of TiO₂, the action of hydrogen has become controversial in recent years, with claims that surface disorder is responsible for the enhanced photoactivity induced by exposure to hydrogen. The many published experimental and density-functional-theory modelling studies are surveyed with the aims of determining what is agreed or contested, and relating defect structure to band structure. It is concluded that further work is needed to clarify the mechanisms of defect production and defect diffusion, as well as the origins of the numerous sample colours observed following treatment in vacuum or hydrogen.

Chalcogenide lone pair semiconducting materials are important materials due to their prospective applications in thermoelectrics, phase change memories, topological insulators etc. Investigating these lone pair semiconductors for versatile applications, different electronic properties were studied by researchers world-wide. Analyses of these semiconducting materials in bulk and thin films for electronic properties like dark and photo-conductivity, photosensitivity, carrier concentration, carrier type, relaxation time and thermopower are the major constituents while accepting them for applications. This review stresses on the electronic properties of several binary, ternary and quaternary lone pair chalcogenide systems. The electronic properties are generally discussed on the basis of chemical ordering in system. A brief discussion on some theoretical background of conduction mechanism has also been incorporated for new researchers in this field. Potential applications of chalcogenide semiconducting materials have been outlined.

Advances in the device fabrication in all emerging fields with promising features and improved control on material properties provide a strong motivation for researchers to reveal, recognize the potential of existing materials and to develop new ones with excellent properties by scheme a low cost syntheses method. Since the discovery of abundant, inorganic mayenite electride, [Ca₂₄Al₂₈O₆₄]⁴⁺(e⁻)₄ (thereafter, C12A7:e⁻) (2003), it has attracted much attention due to its unique and unconventional properties such as high electron concentration (∼2.3–7 × 10²¹ cm⁻³) and low work function (WF∼2.4 eV), which are comparable value with alkali metals, but is chemically inert in an ambient atmosphere. Furthermore, a severe reducing environment enables us to substitute electrons almost completely for anions in the cages, forming a stable inorganic electride, C12A7:e⁻. Finally, the formation of these active anions in this material has potential application as a catalyst support in the NH₃ synthesis/decomposition, CO₂ dissociation and specially recently introduced by our group as electrocatalyst in fuel cell. To further boost these applications the important thing was to synthesize high specific surface area, nanosized C12A7:e⁻ powder with enhanced conductivity, that can be done by cation doping. Over the last decade, experimental studies supported by theoretical calculations have demonstrated that cation elements doping can further boost its electrical properties. Therefore, our group studied doping with more suitable cations, Si, Sn, Ga, V etc in C12A7:e⁻ and we will explain each in detail. In this review we are going to describe progress in the synthesis of C12A7:e⁻ especially in nanosized powder material, and about most important recent challenges towards the suitable cations doping in C12A7:e⁻ electride and finally its industrial important applications as a catalyst.

Spin glass state originating from the magnetic frustration due to the geometric arrangement or cation disorder is an interesting topic of research. FeNbO₄, exhibiting multifarious applications, crystallizes mainly in three different polymorphic forms with cation ordered and disordered structures. Despite their antiferromagnetic nature, the orthorhombic (o-FeNbO₄) and monoclinic FeNbO₄ (m-FeNbO₄) polymorphs exhibit a difference in their magnetic properties at low temperatures. Here, we report our observation of spin glass behaviour of o-FeNbO₄ with a cation disordered structure. Our work is a combined experimental and theoretical study of structure-magnetic property relations of the antiferromagnetic o- and m-FeNbO₄ with the Néel temperatures of 30 and 46 K, respectively. o-FeNbO₄ contrasted itself from m-FeNbO₄ as a spin glass by exhibiting field-dependent bifurcation in ZFC and FC magnetization, frequency-dependent AC susceptibility, memory effect, thermoremanence, and anamoly in the heat capacity. The presence of antiphase domains and boundaries due to cation order/disorder in both the structural polymorphs was evidenced from the electron diffraction analyses that account for the observed low temperature magnetic interactions. Further, modeling the structures with varying amounts of cation disorder using first principles calculations revealed the structural stability and competing spin interactions that support our experimentally observed spin glass behaviour of o-FeNbO₄.

Ternary transition metal nitrides (TTMNs) have acquired substantial attention due to the ability to offer for tuning properties. Furthermore efforts to develop new TTMNs have resulted in the development of new syntheses approaches. In this review, recent progress made regarding investigations on electronic structure, stoichiometry, crystal structures, synthesis and applications are reviewed. Intermediate bonding in these solids exist in the structure types revealed so far. Bonding in these systems are an intriguing mix of ionic (oxide-like) and covalent (carbide-like). This enhances the possibilities of finding unique structures (i.e. anti-fluorite analogous [1]). A good case in point is the Delafosite types and η-nitrides structures found commonly in TTMNs which are typically associated with ABO_x type oxides and carbides. Due to the rich structural chemistry associated with TTMNs, their study is considered a growing area in solid state and applied chemistry. Advancement made in the synthesis of powder and thin film materials of TTMNs are discussed. The powder methods involve the following methods: solid state, high-pressure-high temperature, solvothermal method, ammonothermal method, sol-gel method, Pechini method, temperature-programmed reduction, thermal degradation of metal complex, solid-state metal oxide-organic reaction, solid state ion exchange reaction, and electrodeposition replacement method. On the other hand, the TTMN thin film fabrication is based on two types of methods; physical vapor deposition (PVD) and chemical vapor deposition (CVD) method. The PVD involve deposition using different ways using laser or plasma based approaches (eg. pulsed laser deposition (PLD)) and magnetron sputtering. Chemical vapor deposition methods involve electrodeposition reaction method. Among all synthesis methods, the sol-gel process following the ammonolysis is considered comparatively better for large scale production owing to the simple apparatus setup. Different synthesis methods are deployable based on the application at hand. Applications can be range from electrocatalysts in ORR reaction [2,3], electrocatalysts as sensor [4], supercapacitors [2,3,5], solar cell [6], magnetic, superconducting [7], hard coating materials [8] e.g. protective, functional, conductive, wear-resistance and decorative coating, NH₃ synthesis [9], and hydrogenation process in hydrocarbon reactions [10].

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.