Progress in Solid State Chemistry最新文献

This article investigates the densification of AlN ceramics through both Gas Pressure Sintering (GPS) and Spark Plasma Sintering (SPS) methods, employing cerium aluminates (CeAlO₃) as sintering aids and comparing their influence to that of the usual cerium oxide (CeO₂). While sintering aids like CeO₂ promote densification, CeAlO₃ exhibited lower reactivity during both SPS and GPS sintering. Chemical reactions between cerium oxide and aluminium oxide primarily involved the reduced phase as cerium sesquioxide (Ce₂O₃). On the basis on the Ce₂O₃–Al₂O₃ pseudo-binary system, the formation of secondary phases, such as CeAlO₃ and CeAl₁₁O₁₈, during sintering was explained and confirmed by XRD. From complementary characterizations, it has been shown that sintering significantly impacted secondary phase composition and distribution. By employing specific densification cycles, SPS yielded smaller grains and thicker secondary phase cordons which led to enhanced electrical conductivity. Conversely, GPS produced coarser microstructures including larger grains and a network of secondary phases and some agglomerations at the triple points. These modifications influenced the overall conductivity. SPSed samples with 3 wt.% CeO₂ and short dwelling times demonstrated higher electrical conductivity, exceeding by about 6 orders of magnitude the electrical conductivity of those obtained by GPS.

Titanium Nitride (TiN) is widely used in many industrial sectors for its outstanding performances including its mechanical properties, high chemical and thermal stability. Associated with its plasmonic behavior, TiN thin films are very promising for the manufacturing of optical metasurfaces devices or new plasmonic materials. Among the processes that make it easy to obtain metal nitride coatings, nitriding of metal oxide films has become increasingly popular in recent years. A multitude of synthesis processes can be used to obtain TiO₂ films, with different crystalline states (amorphous, anatase or rutile) depending on the technique used, which can then be converted into TiN coatings. In this paper, the effect of the initial crystalline state of TiO₂ layers was investigated on the structural properties, plasmonic properties and the friction behavior of TiN thin films obtained by Rapid Thermal Nitridation (RTN). The results indicate that, regardless of the crystalline state of the starting TiO₂ film, the RTN process leads to complete nitridation of TiN coating. Moreover, even though surface morphology and friction properties differ slightly, depending on the crystallization of the starting TiO₂, plasmonic properties remain very similar, thus highlighting the great versatility and uniformity of this nitriding technique, enabling TiN to be produced for a wide range of applications.

We present a range of inverse perovskite nitrides with an elpasolite-type superstructure. (Ca₃N_0.682(9))Sn and (Ca₃N_0.559(7))Pb are variants of the previously described (Ca₃N)Sn and (Ca₃N)Pb which contain less nitrogen and crystallize in $Fm\bar{3}m$. (Ba₃N_0.5)Sn and (Ba₃N_0.5)Pb resemble the previously reported perovskites (Ba₃N_x)Sn and (Ba₃N_x)Pb, but with both the superstructure and octahedral tilting, resulting in space group $R\bar{3}$. (Ca₃N_0.77(2))Si, (Ca₃N_0.669(6))Ge, (Sr₃N_0.5)Ge and (Ba₃N_0.5)Ge all crystallize in P2₁/n. Among these, only (Ca₃N_x)Ge has been previously described as (Ca₃N)Ge. (Ca₃N_0.77(2))Si is notably the first compound in which mutually isolated N³⁻ and Si⁴⁻ ions coexist. There also exists a version with composition (Ca₃N_0.86(6))Si, which crystallizes in the cubic perovskite aristotype structure with space group $Pm\bar{3}m$. Similarly, there are versions of (Sr₃N_0.5)Ge, (Ba₃N_0.5)Sn and (Ba₃N_0.5)Pb with elevated nitrogen contents, less strongly tilted octahedra and no apparent superstructure. Electronic structure calculations indicate a metallic nature of the title compounds, with rather narrow improper band gaps for the strontium and barium compounds.

From crystal chemistry and density functional theory DFT calculations, a stepwise rationale is proposed for the transformation from standalone distorted tetrahedron α-C₅ favored over standalone regular tetrahedron β-C₅ to high density – ultra hard orthorhombic α-C₆ and β-C₆ with qtz (quartz-based) topology characterized by 3D arrangements of distorted tetrahedra to lower density dia-C topology (diamond-like, with regular C4 tetrahedra). Progressive C insertions into orthorhombic α-C₅, α-C₆, and lastly into C₇ were operated leading to ultimate C₈ stoichiometry identified as diamond-like. C₇ was also used as template to devise C₃N₄ carbonitride with exceptional mechanical properties. The induced structural and physical changes are supported with elastic properties pointing to ultra-hardness, larger for qtz α,β-C₆ than dia C₈ and inferred dynamic stability for all stoichiometries from the phonons band structures. The thermodynamic quantities as the specific heat were compared with diamond experimental C_V. The electronic band structures reveal semi-conducting C₆, metallic C₇ characterized by diamond-defect structure, and insulating C₈. The results are meant to help further systemic understanding of tetrahedral carbon allotropes.

Interest in perovskite solar cell (PSC) research is increasing because PSC has a remarkable power conversion efficiency (PCE), which has notably risen to 28.3 %. However, commercialization of PSCs faces a significant obstacle due to their stability issues. This review article primarily focuses on several key aspects of PSCs, including different types of solar cells, their construction and operational mechanisms, efficiency, and overall stability. It explains the structure and functioning of PSCs, covering materials and components used for absorber layer, electron-transport layer, hole-transport layer, and electrodes. This review emphasized stability challenges associated with PSCs and discussed various factors and issues contributing to the degradation of these solar cells over time. It then provided a concise overview of different strategies and ongoing efforts taken to enhance the stability of PSCs. It also summarized various approaches used to improve their durability. In summary, this article offers a comprehensive exploration of PSCs, encompassing their construction, operation, improvement in efficiency, and obstacles related to their long-term stability. Furthermore, it addresses factors influencing PSC stability and outlines future challenges, focusing on prolonging their lifespan and enhancing stability for broader applications. Finally, this article has tackled various possible solutions to address the challenges encountered by the PSCs.

Fe³⁺-activated near-infrared (NIR) luminescent materials have attracted growing research interests for their tunable broadband emission and extensive application potentials in the fields of night vision, biomedical imaging, nondestructive food analysis, etc. Deep insight into the relation between crystal structure and luminescence performance plays a significant role in developing novel efficient NIR functional materials. In this review, after a brief introduction, we first discuss the mechanism of Fe³⁺ luminescence in octahedral and tetrahedral crystal fields based on the Tanabe-Sugano energy level diagram. Next, the research progress of Fe³⁺-doped NIR luminescent materials, including structure, property and potential application, is summarized, followed by the strategies to enhance NIR steady-state luminescence, persistent luminescence and mechanoluminescence performances. Then we conduct a comparison of luminescence efficiency and luminescence thermal stability of Fe³⁺-doped NIR materials. At last, we propose several challenges and outlooks in the research of Fe³⁺-activated NIR luminescent materials. This review is aimed to provide a deeper understanding of not only Fe³⁺ luminescence mechanism but also the current research progress of Fe³⁺-doped materials, so as to provide constructive strategy in the exploitation of efficient Fe³⁺-activated NIR luminescent materials.

This review presents an overview on the structures and electrical properties of B-site deficient hexagonal perovskite oxides, which have been receiving increasing attention as key components as dielectric resonators in microwave telecommunications, as well as solid-state oxide ion and proton conductors in solid oxide fuel cells. The structural evolution and stability, order-disorder of cation and anions, and mechanisms underlying the dielectric and ionic conduction behaviors for the B-site deficient hexagonal perovskites are summarized and the roles of the B-site deficiency on the structural stability and option, ion order-disorder and electrical performance are highlighted. This provides useful guidance for design of new hexagonal perovskite oxide materials and structural control to enhance their electrical properties and discover new functionality as dielectric resonators and solid-state ionic conductors.

The undesirable capacity degradation of LiMnPO₄ upon cycling at high temperatures is a challenge to its practical application. Herein, a lattice doping strategy is adopted to improve the high-temperature cycling stability of LiMnPO₄, and the comparative study reveals that Al³⁺ doping into LiMnPO₄ in a form of Li_0.98Al_0.02MnPO₄ is highly beneficial to the cycling performance of LiMnPO₄ and the capacity retention can be significantly improved from 67.4 % to 93.4 % after 100 cycles at 1C at 60 °C, because Al³⁺ doping can effectively reduce passivation products deposition on the cathode and manganese dissolution in the electrolyte, which thus improve the cathode/electrolyte interface and stabilize the structure of LiMnPO₄ at high temperatures.

Chromophores at different coordinations can give rise to different colors; usually, chromophores at non-centrosymmetric coordinations are preferred for intense pigments. Different solid solutions M_2-xCo_xM’O₄ (M = Mg/Zn, and M’ = Ti/Sn) with inverse spinel structure were synthesized with the goal of understanding color variation with site distribution, as the chromophore Co²⁺ in these solid solutions can occupy either the tetrahedral or octahedral sites or both depending on the composition. Another goal was to develop environmentally friendly and cheap blue pigments by reducing the carcinogenic cobalt to obtain a similar color to that of commercially available cobalt blue, which uses a significant amount of Co²⁺ (33.31 % by mass). For Mg_2-xCo_xTiO₄ series, turquoise blue hues were observed for low cobalt content, and different shades of blue were observed for Mg_2-xCo_xSnO₄ series with a color similar to cobalt blue, including just 4.90% of cobalt by mass. While for Zn_2-xCo_xTiO₄, and Zn_2-xCo_xSnO₄ series, different shades of brown and different shades of green, respectively, were observed. One of the main reasons behind the major difference in color for the Mg and Zn containing solid solutions, regardless of the same chromophore in the same structure is related to the chromophore site distribution in the system. For the Mg-containing solid solutions, different shades of blue are observed as Mg has no preference for any of the sites, Co²⁺ mostly goes to tetrahedral sites. In contrast, for the Zn-containing solid solutions, no blue shades were observed because of the strong preference of Zn for the tetrahedral sites owing to the sp³ hybridization, which in turn forces Co²⁺ to occupy the octahedral sites. Neutron refinement proves that Co²⁺ occupies mainly tetrahedral sites in the Mg-containing solid solutions and mostly octahedral sites in the Zn-containing solid solutions.