Progress in Solid State Chemistry最新文献

Infrared nonlinear optical (IR-NLO) crystals with excellent properties are in extensive demand due to their important role in IR laser technology. Currently, it remains a great challenge to obtain IR-NLO materials with both high second harmonic generation (SHG) response and large laser-induced damage thresholds (LIDTs). Some structural design strategies such as ‘structural/functional regions’ have been adopted to develop new high-performance NLO materials. The covalent structural region producing SHG signals has been extensively investigated, whereas the hard cations (alkali, alkaline-earth, and rare-earth metal ions) which are responsible for improving LIDTs, have been relatively neglected. Utilizing the concept of structural/functional regions, we focus on the relation between structural regions and SHG properties in chalcogenides. Combining different kinds of hard cations can change the dimension of structures and affect the stacking of NLO-active groups. Introducing more hard cations and constructing more complex ion regions help to increase the laser damage threshold. Based on the mentioned structural strategies, guidance will be provided for developing high-performance multiple-cation materials for IR NLO applications.

Two-dimensional (2D) materials have attracted much research attention in the last ten years, resulting in significant advancements in their theoretical and technical understanding. Since the successful fabrication of 2D graphene, various types of graphene-like 2D materials, such as transition metal dichalcogenides (TMDCs), metal carbides or nitrides (MXenes), hexagonal boron nitride (h-BN), layered double hydroxides (LDHs), and halide perovskites, have drawn significant attention and developed into the most promising semiconductor materials in the area of optoelectronic devices. Recently, several studies have been reported indicating the exciting optoelectronic properties of these 2D materials. In this review, the properties and applications of different 2D materials, including TMDCs, halide perovskites, and MXenes, are discussed briefly. Firstly, the basic properties of these 2D materials, particularly those pertaining to optoelectronic properties, are described. Then, the most recent studies on 2D-based optoelectronic applications, such as solar cells, photodetectors, and LEDs, are studied. The conclusion provides some viewpoints on the current challenges and potential future applications of these 2D materials. This article provides a comprehensive, authoritative, critical, and accessible review of general interest to the materials science research community, including beginners and experts. Its comprehensive approach, mechanistic insights, real-world applications, and relevance to materials science justify its value as an authoritative and accessible resource.

The present study aims to describe the role of the grain size on the properties of submicron- and nano-structured Ba_0·8Sr_0·2TiO₃ (BST) ceramics. Dense (1 − 2% porosity) ceramics with average grain sizes in the range of (77 − 234) nm were consolidated under different spark plasma sintering conditions starting from nanopowders with a mean particle size of 70 nm, synthesized via the acetate variant of the sol-gel method. The structural analysis based on XRD data revealed a mixture of cubic and tetragonal modifications at room temperature for the precursor powders and for all the investigated ceramics. The structural heterogeneity of the individual ceramic grains with coexistence of cubic and tetragonal polymorphs was confirmed by HR-TEM investigations. Accordingly, a “brick-wall" model with cubic grain boundary regions and tetragonal grain cores is proposed. By increasing the grain size, from 77 to 234 nm, a decrease of the phase transitions diffuseness accompanied by an increase of the permittivity maxima (from 650 to 4500) and dielectric losses (from 5 to 7.5%, at 100 Hz), was detected by broadband dielectric spectroscopy. No variation of the Curie temperature in the investigated Ba_0·8Sr_0·2TiO₃ ceramics was detected, unlike typically reported for BaTiO₃ ceramics with similar grain sizes. The Curie-Weiss temperature and the Curie constant decrease when grain size is diminished, indicating an overall reduction of the ferroelectric active volume, as a scaling effect. The ferroelectric switching was demonstrated for all the selected fine-grained BST ceramics, either at nanoscale or macroscopically, with an increased ferroelectric character for the coarser submicron-structured ceramics, with respect to the nanocrystalline one. The observed properties of the fine-grained Ba_0·8Sr_0·2TiO₃ ceramics are explained in the frame of multiphase coexistence and ferroelectricity “dilution” due to the increasing role of non-ferroelectric grain boundaries when reducing grain size and complete the knowledge on the scale-dependent properties of dense fine-grained BaTiO₃-based ceramics.

Cemented carbides have enjoyed widespread applications as a function of their outstanding properties during the past 100 years. Despite the advantages, however, recently there have been concerns about the challenges associated with traditional cemented carbides, i.e. the conflict of properties (hardness and toughness, strength and wear resistance) as well as the instability of reliability in service, necessitating the development of functional gradient cemented carbides (FGCCs). Although recent decades, investigations have seen explosive growth in FGCCs, there is still a lack of comprehensive review on FGCCs. Herein, the current study applies towards summarize the progress of FGCCs during the past 60 years, emphasizing the demand in FGCCs with tailored properties and customized requirements for specific applications. We initially introduce basic cognition of FGCCs, subsequently, comprehensively elucidate the gradient formation mechanisms of carburization, decarburization, nitridation, denitrification, infiltration process, and construction methods (solid-phase sintering, graphene doping and additive manufacturing etc.), then summary processing techniques and mechanical properties of FGCCs. In addition, the impart of additive on further improving the properties of FGCCs is discussed. Afterward, the possible applications of FGCCs at different areas are proposed. At the end of this paper, a summary of concluding remarks and potential developed direction of state-of-the-art FGCCs is provided.

Solar water-splitting using particle photocatalysts is a promising approach to sustainably produce hydrogen. LaTiO₂N is an auspicious visible light absorbing photocatalyst regarding the oxygen evolution reaction. In this work, the topotactic growth mechanism of LaTiO₂N particles is investigated by varying the precursor material and the synthesis conditions during thermal ammonolysis. Their influence is discussed in regard to structure, composition, morphology, optical, and functional properties. Using the conventional, layered perovskite oxide, La₂Ti₂O₇, as precursor resulted in brick-shaped porous LaTiO₂N particles with a high degree of crystallinity and a high surface area. When adding flux, the increased mobility during thermal ammonolysis leads to larger morphology changes resulting in non-porous, perforated particles with skeletal features. In a novel, alternative approach, LaTiO₂N is prepared via the topotactic conversion of a double-layered Sillén-Aurivillius type oxyhalide material, La_2·1Bi_2·9Ti₂O₁₁Cl. The facile formation of LaTiO₂N results in a perforated porous structure exhibiting skeletal features whilst maintaining a high surface area due to the presence of pores. By alternating the morphology of the material in this matter the oxygen evolution under one sun illumination is improved by around 10% or 30% depending on whether thermal ammonolysis of La₂Ti₂O₇ is performed with or without flux, respectively.

The last two decades have seen a growing trend towards sizable single crystals of REBa₂Cu₃O_7−δ (RE123, RE = rare earth elements) with fine quality, which have been attracting considerable interest in the study of superconductivity. As an advanced and classic method, top-seeded solution-growth (TSSG) is the only technique to date for producing RE123 single crystals with dimensions of 2 cm, e.g., a Y123 single crystal of 19.8 × 19.5 mm² in a-b plane and 16.5 mm in height. Recently, novel approaches were developed such as crystal-pulling combined with continual cooling for rapid growth to attain a large-sized RE123 crystal, and the utilization of dopant-added crucibles for continuous growth to produce highly-uniform doped-Y123 crystals. Consequently, researchers from several tens of physical laboratories worldwide have been benefiting from TSSG-produced RE123 single crystals and generating excellent collaborative work. This paper provides an overview of the progress and achievements on the growth of superior RE123 single crystals by TSSG for fundamental studies and practical applications, focusing on three aspects including crystal enlargement, RE123 stoichiometry control and cation doping. The mechanism of crystal growth and the correlation between phase formation and superconducting properties are comprehensively elucidated on the basis of distinctive features of phase diagrams of RE–Ba–Cu–O systems.

Perovskite-type oxynitrides are a new class of inorganic materials that have potential applications as photocatalysts, inorganic pigments and dielectrics. Design of the morphology in conjunction with new synthesis methods is essential for their practical use. In this review, we present the formation of fine particles via a low temperature and ammonia-free synthesis method, the morphology of the oxynitride perovskites obtained using metal carbodiimide, and the toughness of the sintered ceramics in relation to their microstructure.

Making highly efficient and stable perovskite solar cells (PSCs) are often based on the processing techniques, band gap of the material and effective interface charge separation. The efficiency of PSCs can be enhanced through several methods including the utilization of a solar-friendly absorber, interface passivation and the implementation of multi-junction spectrally matched absorbers or bilayered phase homojunction (BPHJ) consisting of identical absorbers. Here, we demonstrated BPHJ concept by stacking identical compositions of highly efficient and stable FA_0.15MA_0.85PbI₃ perovskite absorbers adopting solution process (SP) and thermal evaporation (TEV) techniques. We successfully achieved FA_0.15MA_0.85PbI₃ (SP)/FA_0.15MA_0.85PbI₃-(TEV) based BPHJ normal n-i-p devices, which significantly crossing 22.

% PCE. These improvement stems from effective deposition method for achieving high-quality FA_0.15MA_0.85PbI₃-based BPHJ enabling smooth charge transfer at the interfaces. The resulting BPHJ-based champion device achieve a 22.13 % PCE and retain >95 % its original efficiency over 1000 hours.

Lithium-rich manganese-based transition metal oxide Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) can achieve high energy density due to the interaction of anionic redox kinetics in Li₂MnO₃. However, the irreversible release of oxygen and migration of Mn ions during deep de-lithiation disrupts the layer structure of LNMO, leading to a decrease in voltage and capacity. Herein, we confine oxygen anion through Zr and Al co-doping. Combined analysis of structure refinement, XPS and XAS, the co-doped strategy effectively prohibits cation disordering of Li/Ni, inhibits the Jahn-Teller effect and reduces the transition metal (TM) and oxygen hybridization. As a result, the Zr and Al co-doping LNMO sample (ZA-LNMO) possesses a capacity retention of 92% after 100 cycles and 86% after 200 long-term cycles, much higher than the value of the undoped sample (79% for 100 cycles and 58% for 200 cycles). Even at the harsh conditions such as ultra-high current rate (10 C) or high temperature (60 °C), ZA-LNMO also maintains 70% retention after 200 cycles. Our findings provide an insight into the synergistic effect of cation co-doping and help to design layered oxides for future applications.

Perovskite-type oxynitrides ACa_0.2M_0.8O_2.6N_0.4 (A = Sr, Ba; M = Nb, Ta) were synthesized via the ammonolytic reaction between A₅M₄O₁₅ and CaCl₂, where the Ca²⁺ insertion and O²⁻/N³⁻ substitution occurred cooperatively. In terms of the average structure, SrCa_0.2Nb_0.8O_2.6N_0.4 and SrCa_0.2Ta_0.8O_2.6N_0.4 belong to the orthorhombic Pnma space group, and BaCa_0.2Nb_0.8O_2.6N_0.4 and BaCa_0.2Ta_0.8O_2.6N_0.4, the primitive cubic Pm $\bar{3}$ m group. The comparison between the experimental lattice volume and the summed ionic volume suggested that ACa_0.2M_0.8O_2.6N_0.4 have higher degrees of ionicity than AM'_0.2M_0.8O_3−xN_x (M′ = Li, Mg, Mn), but are more covalent than ANa_0.2M_0.8O_2.8N_0.2. Despite the significant mismatches of size and charge between Ca²⁺ and Nb⁵⁺ (or Ta⁵⁺), no cation ordering was detected on the octahedral site. On the other hand, the O/N distribution appeared to depend on the bonding geometry around the anion sites in a way N favors the straighter bonding connectivity of M−N−M. The band gap energies of ACa_0.2M_0.8O_2.6N_0.4 were estimated to be 1.9–2.25 eV depending on A and M. The band gaps and color properties of AMO₂N and AM'_0.2M_0.8O_3−xN_x (A = Sr, Ba; M = Nb, Ta; M′ = Li, Na, Mg, Ca, Mn) are compared. Thermogravimetry and differential scanning calorimetry were conducted in the air to assess the oxynitride stability. The electrical behaviors were studied by the equivalent circuit analysis of the impedance spectrum using compacted polycrystalline specimens, where BaCa_0.2Ta_0.8O_2.6N_0.4 was found to possess a bulk dielectric constant of 4550 along with an electrical conductivity of ≈10⁻⁶ S/cm at 27 °C. It remains, however, necessary to assess the extrinsic effects arising from the non-ideal sintering to interpret thoroughly the electrical property of BaCa_0.2Ta_0.8O_2.6N_0.4.