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ConspectusTwo-dimensional (2D) nanomaterials have attracted increasing research interest since mechanically exfoliated graphene was obtained in 2004. The ultrathin thickness and relatively large lateral size of 2D nanomaterials render them various intriguing properties such as compelling electronic properties, ultrahigh specific surface area, excellent mechanical properties, and so on. A wide range of 2D nanomaterials, including graphene and its derivatives, transition metal dichalcogenides (TMDs), metals

Covalently bonded ceramics exhibit preeminent properties—including hardness, strength, chemical inertness, and resistance against heat and corrosion—yet their wider application is challenging because of their room-temperature brittleness. In contrast to the atoms in metals that can slide along slip planes to accommodate strains, the atoms in covalently bonded ceramics require bond breaking because of the strong and directional characteristics of covalent bonds. This eventually leads to catastrophic failure on loading. We present an approach for designing deformable covalently bonded silicon nitride (Si 3 N 4 ) ceramics that feature a dual-phase structure with coherent interfaces. Successive bond switching is realized at the coherent interfaces, which facilitates a stress-induced phase transformation and, eventually, generates plastic deformability.

Hybrid nanomaterials with controlled dimensions, intriguing components and ordered structures have attracted significant attention in nanoscience and technology. Herein, we report a facile and green polyoxometallate (POM)-assisted hydrothermal carbonization strategy for synthesis of carbonaceous hybrid nanomaterials with molecularly dispersed POMs and ordered mesopores. By using various polyoxometallates such as ammonium phosphomolybdate, silicotungstic acid, and phosphotungstic acid, our approach can be generalized to synthesize ordered mesoporous hybrid nanostructures with diverse compositions and morphologies (nanosheet-assembled hierarchical architectures, nanospheres, and nanorods). Moreover, the ordered mesoporous nanosheet-assembled hierarchical hybrids with molecularly dispersed POMs exhibit remarkable catalytic activity toward the dehydration of tert-butanol with the high isobutene selectivity (100 %) and long-term catalytic durability (80 h).

Summary Two-dimensional (2D) nanomaterials have attracted increasing interest because of their compelling physicochemical properties and promising applications. Recent studies have demonstrated that phases of nanomaterials could significantly affect their properties and applications because of the distinct atomic arrangements. Besides crystalline phases, the amorphous nanomaterials, which lack long-range atomic ordering, and heterophase nanostructures consisting of more than one phase have also shown enhanced performances in some specific applications. Recently, with the rapid development in phase engineering of nanomaterials (PEN), the controlled synthesis of 2D nanomaterials with unconventional phases and the exploration of phase-dependent properties and applications have been witnessed. In this perspective, we briefly summarize the research progress on 2D nanomaterials with unconventional phases, including unconventional crystal phases, amorphous phase, and heterophase. On the basis of different material categories, we highlight their synthetic methodologies, unique structures, and intriguing properties. Finally, we provide personal insights on challenges and potential research opportunities in this emerging field.

The crystal phase of nanomaterials is one of the key parameters determining their physicochemical properties and performance in various applications. However, it still remains a great challenge to synthesize nanomaterials with different crystal phases while maintaining the same composition, size, and morphology. Here, a facile, one-pot, wet-chemical method is reported to synthesize Pd3 Sn nanorods with comparable size and morphology but different crystal phases, that is, an ordered intermetallic and a disordered alloy with L12 and face-centered cubic (fcc) phases, respectively. The crystal phase of the as-synthesized Pd3 Sn nanorods is easily tuned by altering the types of tin precursors and solvents. Moreover, the approach can also be used to synthesize ternary PdCuSn nanorods with the L12 crystal phase. When used as electrocatalysts, the L12 Pd3 Sn nanorods exhibit superior electrocatalytic performance toward the ethanol oxidation reaction (EOR) compared to their fcc counterpart. Impressively, compared to the L12 Pd3 Sn nanorods, the ternary L12 PdCuSn nanorods exhibit more enhanced electrocatalytic performance toward the EOR, yielding a high mass current density up to 6.22 A mgPd -1 , which is superior to the commercial Pd/C catalyst and among the best reported Pd-based EOR electrocatalysts. The authors would like to acknowledge the Facility for Analysis, Characterization, Testing, and Simulation, Nanyang Technological University, Singapore, for their electron microscopy (and/or X-ray) facilities. Z.F. and H.Z. thank the financial support from ITC via Hong Kong Branch of National Precious Metals Material Engineering Research Center (NPMM), and the Start-Up Grants (Project Nos. 9610480, 9380100, and 7200651) and grants (Project Nos. 9610478, 9680314, 7020013 and 1886921) in City University of Hong Kong. The authors thank the computational resources from the Big Data Center of Southeast University and National Supercomputing Center of Tianjin.

With the development of phase engineering of nanomaterials (PEN), construction of noble-metal heterostructures with unconventional crystal phases, including heterophases, has been proposed as an attractive approach toward the rational design of highly efficient catalysts. However, it still remains challenging to realize the controlled preparation of such unconventional-phase noble-metal heterostructures and explore their crystal-phase-dependent applications. Here, various Pd@Ir core-shell nanostructures are synthesized with unconventional fcc-2H-fcc heterophase (2H: hexagonal close-packed; fcc: face-centered cubic) through a wet-chemical seeded method. As a result, heterophase Pd66 @Ir34 nanoparticles, Pd45 @Ir55 multibranched nanodendrites, and Pd68 @Ir22 Co10 trimetallic nanoparticles are obtained via the phase-selective epitaxial growth of fcc-2H-fcc-heterophase Ir-based nanostructures on 2H-Pd seeds. Importantly, the heterophase Pd45 @Ir55 nanodendrites exhibit excellent catalytic performance toward electrochemical hydrogen evolution reaction (HER) under acidic conditions. An overpotential of only 11.0 mV is required to achieve a current density of 10 mA cm-2 on Pd45 @Ir55 nanodendrites, which is lower than those of the conventional fcc-Pd47 @Ir53 counterparts, commercial Ir/C and Pt/C. This work not only demonstrates an appealing route to synthesize novel heterophase nanomaterials for promising applications in the emerging field of PEN, but also highlights the significant role of the crystal phase in determining their catalytic properties.

Crystal phase engineering of noble-metal-based alloy nanomaterials paves a new way to the rational synthesis of high-performance catalysts for various applications. However, the controlled preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases still remains a great challenge due to their thermodynamically unstable nature. Herein, we develop a robust and general seeded method to synthesize PdCu alloy nanomaterials with unconventional hexagonal close-packed (hcp, 2H type) phase and also tunable Cu contents. Moreover, galvanic replacement of Cu by Pt can be further conducted to prepare unconventional trimetallic 2H-PdCuPt nanomaterials. Impressively, 2H-Pd67Cu33 nanoparticles possess a high mass activity of 0.87 A mg-1Pd at 0.9 V (vs reversible hydrogen electrode (RHE)) in electrochemical oxygen reduction reaction (ORR) under alkaline condition, which is 2.5 times that of the conventional face-centered cubic (fcc) Pd69Cu31 counterpart, revealing the important role of crystal phase on determining the ORR performance. After the incorporation of Pt, the obtained 2H-Pd71Cu22Pt7 catalyst shows a significantly enhanced mass activity of 1.92 A mg-1Pd+Pt at 0.9 V (vs RHE), which is 19.2 and 8.7 times those of commercial Pt/C and Pd/C, placing it among the best reported Pd-based ORR electrocatalysts under alkaline conditions.

The crystal phase of nanomaterials is one of the key parameters determining their physicochemical properties and performance in various applications. However, it still remains a great challenge to synthesize nanomaterials with different crystal phases while maintaining the same composition, size, and morphology. Here, a facile, one-pot, wet-chemical method is reported to synthesize Pd

In this paper, α-Si 3 N 4 nanobelts assembled by Si 3 N 4 microcrystals on the nanowires were synthesized from amorphous Si 3 N 4 powders that were prepared by thermolysis of silicon diimide powders. By prolonging the heating time at 1550 °C, the amorphous Si 3 N 4 powders were converted to hexagonal phase α-Si 3 N 4 microcrystals which were adhered to the surface of nanowires to obtain α-Si 3 N 4 nanobelts. The obtained α-Si 3 N 4 nanobelts were hollow in the centre with a width of ∼850 nm and a thickness of ∼150 nm. Microcrystals were deposited on the surface of 2–3 parallel nanowires. The diameter of the Si 3 N 4 microcrystals was 30–230 nm, and the diameter of the nanowires was 50–100 nm. Evaporation of the amorphous Si 3 N 4 powders released Si vapour and N vapour, which led to the formation of the Si 3 N 4 microcrystals. The nanowires grew on the surface of the amorphous Si 3 N 4 powders due to the nucleation and diffusion of Si and N atoms of amorphous Si 3 N 4 powders. The growth mechanism of the products with unique morphology can be considered as a combination of vapour-solid mechanism and secondary nucleation process.

The nucleation pathway determines the structures and thus properties of formed nanomaterials, which is governed by the free energy of the intermediate phase during nucleation. The amorphous structure, as one of the intermediate phases during nucleation, plays an important role in modulating the nucleation pathway. However, the process and mechanism of crystal nucleation from amorphous structures still need to be fully investigated. Here, in situ aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is employed to conduct real-time imaging of the nucleation of ultrathin amorphous nanosheets (NSs). The results indicate that their nucleation contains three distinct stages, i.e., aggregation of atoms, crystallization to form lattice-expanded nanocrystals, and relaxation of the lattice-expanded nanocrystals to form final nanocrystals. In particular, the crystallization processes of various amorphous materials are investigated systematically to form corresponding nanocrystals with unconventional crystalline phases, including face-centered-cubic (fcc) Ru, hexagonal-close-packed (hcp) Rh, and a new intermetallic IrCo alloy. In situ electron energy-loss spectroscopy (EELS) analysis unveils that the doped carbon in the original amorphous NSs can migrate to the surface during the nucleation process, stabilizing the obtained unconventional crystal phases transformed from the amorphous structures, which is also proven by density functional theory (DFT) calculations.

Two-dimensional (2D) metal nanomaterials have gained ever-growing research interest owing to their fascinating physicochemical properties and promising application, especially in the field of electrocatalysis. In this review, we briefly introduce the recent advances in wet-chemical synthesis of 2D metal nanomaterials. Subsequently, the catalytic performances of 2D metal nanomaterials in a variety of electrochemical reactions are illustrated. Finally, we summarize current challenges and highlight our perspectives on preparing high-performance 2D metal electrocatalysts.

Heterostructured, including heterophase, noble-metal nanomaterials have attracted much interest due to their promising applications in diverse fields. However, great challenges still remain in the rational synthesis of well-defined noble-metal heterophase nanostructures. Herein, we report the preparation of Pd nanoparticles with an unconventional hexagonal close-packed (2H type) phase, referred to as 2H-Pd nanoparticles, via a controlled phase transformation of amorphous Pd nanoparticles. Impressively, by using the 2H-Pd nanoparticles as seeds, Au nanomaterials with different crystal phases epitaxially grow on the specific exposed facets of the 2H-Pd, i.e., face-centered cubic (fcc) Au (fcc-Au) on the (002)h facets of 2H-Pd while 2H-Au on the other exposed facets, to achieve well-defined fcc-2H-fcc heterophase Pd@Au core-shell nanorods. Moreover, through such unique facet-directed crystal-phase-selective epitaxial growth, a series of unconventional fcc-2H-fcc heterophase core-shell nanostructures, including Pd@Ag, Pd@Pt, Pd@PtNi, and Pd@PtCo, have also been prepared. Impressively, the fcc-2H-fcc heterophase Pd@Au nanorods show excellent performance toward the electrochemical carbon dioxide reduction reaction (CO2RR) for production of carbon monoxide with Faradaic efficiencies of over 90% in an exceptionally wide applied potential window from -0.9 to -0.4 V (versus the reversible hydrogen electrode), which is among the best reported CO2RR catalysts in H-type electrochemical cells.

A novel freeze drying assisted combustion synthesis route was developed to fabricated Eu2+-activated Ca-Sialon phosphors with high nitrogen content. Highly pure Ca-Sialon powders with 100% uniform elongated grains were obtained at a relatively low nitrogen pressure without using any NH4Cl or NH4F additive. The phosphors exhibited an orangish yellow light peaking at 592 nm under the 450 nm excitation, with optical properties of high quantum efficiencies and very low thermal quenching.

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T') have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T'-phase TMDs, including WS

Utilizing V2O5 powder as starting materials, Vanadium pentoxide (V2O5) nano-sheets were prepared via a first freeze-drying process and following annealing treatment. The phase structure and morphology of as-achieved V2O5 nano-sheets were characterized by powder X-ray diffraction and scanning electron microscopy, respectively. These results demonstrated that V2O5 nano-sheets can be successfully synthesized within the selected region of annealing temperature, and the size and thickness of as-obtained V2O5 nano-sheets were closely associated with the annealing temperature. The catalytic property of V2O5 nano-sheets toward the thermal decomposition of ammonium perchlorate (abbreviated as AP) was assessed. The results indicated that the optimal catalytic property was achieved with V2O5 nano-sheets annealed at 400 °C, which can get the decomposition temperature of AP reduced by 28 °C.

This paper reports the combustion synthesis of α-Si3N4 using green additives of water and alcohol. The addition of water and alcohol is demonstrated to be effective in controlling the reaction kinetics and improving the formation of α-Si3N4 by vapor reactions. With increasing proportion of additives in the starting composition, the content of α-Si3N4 in the product is clearly enhanced. In contrast to the ammonium halides usually employed as additives in the combustion synthesis of α-Si3N4, the green additives used here are nontoxic, noncorrosive, and thus more attractive for industrial applications.

In this contribution, hierarchical micro-/meso-porous SiO2 xerogels were successfully prepared through a Stober methodology coupled with following drying process. The SiO2 xerogels were consisted of nanoparticles of 20–40 nm in size with different contents of water. Fourier transform infrared spectroscopy proved that Si OC2H5 and Si OH groups could be formed in SiO2 xerogels. Further analyses declared that the amount of the Si OC2H5 groups decreased while the concentration of Si OH was firstly increased and then suffered a decline with improving contents of water. Besides, the SiO2 xerogels was endowed with controllable micro-/meso-porous structure. Furthermore, the formation mechanism of the micro-/meso-porous SiO2 xerogels was tentatively put forward. As a consequence, SiO2 xerogels with controllable hierarchical micro-/meso-porous structure could act as the smart material for huge development in catalytic fields.

In this work, an efficient carbothermal reduction–nitridation (CRN) strategy was rationally designed to directly synthesize β-Si3N4 powders with eminent dispersity and granularity uniformity. With the aid of CaO additive, the obtained β-Si3N4 particles were endowed with approximate spherical morphology and smooth surface. The size of β-Si3N4 particles could be regulated in sub-micro and micro scale by altering N2 pressures. More significantly, the underlying growth mechanism of the β-Si3N4 under elevated N2 pressure was comprehensively analyzed and tentatively put forward. Benefiting from the remarkable merits, the as-synthesized β-Si3N4 powders showed great potential for alternative fillers in the application of high thermal conductivity plastic packages. This article is protected by copyright. All rights reserved.

SiAlON phosphors doped with rare earths have attracted much attention on the application of light emitting diode (LEDs) benefitting from their outstanding thermal stability, chemical stability and broad emission band properties. In this work, Eu-doped β-SiAlON green phosphors with composition Si 5.5 Al 0.5 O 0.5 N 7.5 :0.035Eu 2+ were prepared by a highly efficient combustion synthesis (CS) method. The effect of comburent ratios (i.e., Si & Al) were systematically investigated by adjusting the starting compositions of reactants. It was confirmed that the ratios of Si and Al reactants had an intense influence on the phase composition, microstructure and photoluminescence properties of as-synthesized phosphors by directly determining the systematic energy in CS. The as-prepared β-SiAlON:Eu 2+ phosphors featured with high phase purity, uniform particle size of 3–5 μm, well-crystalline morphology and outstanding luminescent properties of green emission under UV or blue excitation were synthesized with 67.5 wt.% ratio of Si and no Al comburent.

Self-propagation high-temperature synthesis (SHS) method was developed as a highly-efficient route for the preparation of Eu-doped β-SiAlON green phosphors. The as-synthesized products with composition Si5.5Al0.5O0.5N7.5:0.035Eu2+ were featured with high phase purity, good uniformity and equiaxed grain morphology. Strong green light emission spectra covering the range of 450–650 nm were obtained under the excitation of UV or blue light. The impacts of the nitrogen pressure in the reaction system and average particle size of Si reactant, which were two of the most vital parameters in the SHS reaction, were systematically investigated. Based on the experimental results, these two factors were confirmed to have striking influences on the phase composition, microstructure and photoluminescence properties of resultant phosphors. In the SHS for β-SiAlON:Eu2+ phosphors, there demonstrated that the selection of N2 pressure of 4 MPa and the utilization of Si reactants with fine particle size would bring about remarkable enhancement in the photoluminescence properties.

In this work, the effects of various additives on the AlN conversion fraction, weight loss, phase compositions and surface morphology during the carbothermal synthesis of spherical AlN granules were investigated in detail. The results inferred that additives played an important role in the improvement of nitridation rate, the formation of spherical morphology and the growth of particle size. The simultaneous addition of CaF 2 and YF 3 resulted in the highest nitridation rate in all samples, while excessive CaF 2 appeared to retard the nitridation process at a particular temperature. However, Ca-aluminates forming in the synthesis process tended to be reduced and further volatilized at high temperature. Furthermore, by analyzing the weight loss during the carbothermal reduction-nitridation process, the reaction mechanisms in the systems using different additives were also attentively disclosed.

Rare earth doped perovskite oxides have attracted much attention due to their multifunctional properties (such as photoluminescence, ferro-/piezoelectricity and so forth). In the current work, Er3+-doped (Li,K,Na)NbO3 nano-ceramics were successfully synthesized by spark plasma sintering and as-obtained ceramics exhibited excellent up-conversion photoluminescence (UC PL) behavior. The influences of the doping of Er3+ on the phase structure, microstructure, and UC PL properties were systematically investigated. The XRD and Raman analysis demonstrated that Er3+ ion entered into A site of (Li,K,Na)NbO3 perovskite structure. The most obvious enhancement of UC PL emission was achieved in the ceramics with 0.25 mol% of Er3+ doped, and the intensity of UC PL emission dropped with the further increase of Er3+ doping. Moreover, it found that two photons contributed to this observed UC PL behavior. These findings here rendered potential application of Er3+ doped (Li,K,Na)NbO3 smart materials in novel multifunctional devices.

Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core-shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu3- χ P nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mgPd -1 , which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mgPd -1 ).

Si3N4 coating is widely used in the production of photovoltaic silicon ingots. This work investigates the influence of pre-oxidation of Si3N4 powders on the interaction between Si3N4 coating and molten Si based on sessile drop experiments. It is found that the surface tension and surface roughness affect the contact angle and accordingly wetting behavior. A new mechanism for the permeation of molten Si in Si3N4 coating is proposed, where the driving force for the permeation is provided by chemical reaction between SiO2 and Si instead of usual capillary force.

Various kinds of amorphous materials, such as transition metal dichalcogenides, metal oxides, and metal phosphates, have demonstrated superior electrocatalytic performance compared with their crystalline counterparts. Compared to other materials for electrocatalysis, noble metals exhibit intrinsically high activity and excellent durability. However, it is still very challenging to prepare amorphous noble-metal nanomaterials due to the strong interatomic metallic bonding. Herein, the discovery of a unique thiol molecule is reported, namely bismuthiol I, which can induce the transformation of Pd nanomaterials from face-centered-cubic (fcc) phase into amorphous phase without destroying their integrity. This ligand-induced amorphization is realized by post-synthetic ligand exchange under ambient conditions, and is applicable to fcc Pd nanomaterials with different capping ligands. Importantly, the obtained amorphous Pd nanoparticles exhibit remarkably enhanced activity and excellent stability toward electrocatalytic hydrogen evolution in acidic solution. This work provides a facile and effective method for preparing amorphous Pd nanomaterials, and demonstrates their promising electrocatalytic application.

Herein, we put forward a simple combustion synthesis strategy for the highly efficient preparation of Eu-doped Ca-α-SiAlON yellow phosphors with different composition of Ca (m/2−x) Eu x Si 12−m-n Al m+n O n N 16−n . The as-synthesized phosphors were endowed with outstanding photoluminescence behavior of yellow emission peaking at ~580 nm under excitation of near-ultraviolet (UV) or blue light. In the designed experiments, products with different compositions, which were determined by the varying m and n values, were obtained by adjusting the proportion of starting reactants. Further, the dependence of composition on the overall properties of products was systematically studied. It was found that the m and n values could have distinct impact on the phase composition, microstructure and photoluminescence properties of as-synthesized phosphors. The most prominent enhancement of spectral intensity was achieved in the sample with composition of m =1.5 and n =0.8 in this research system. The resultant Ca-α-SiAlON:Eu 2+ phosphors were simultaneously featured with high purity, favorable uniformity and equiaxial morphology. A continuous red shift phenomenon in emission wavelength with the increase of m value and an inverse blue shift with the increase of n value were both observed and rationally uncovered.

Herein, a facile combustion synthesis strategy (CS) was constructively developed for the highly-efficient preparation of SiAlON based phosphors. Yellow light emitting behavior was endued to the Ca-α-SiAlON ceramic powders by doping of Eu2 +. The Si average particle size and nitrogen pressure were known to play vital roles in the CS reaction. The distinct impacts of these two important processing parameters on the phase composition, microstructure and photoluminescence properties of products were firstly thoroughly studied in the CS system of Ca-α-SiAlON:Eu2 + phosphors. The experimental results demonstrated that the comprehensive properties of as-synthesized phosphors would be evidently promoted by the utilization of appropriate Si particle size and nitrogen pressure, respectively 4 μm and 5 MPa in this system. The phosphors were featured with high phase purity, good state of crystallization, favorable uniformity and equiaxed morphology. A strong yellow emission was peaked at 576 nm under excitation of near-UV or blue light.

The effect of common impurities, specifically MgO, Al 2 O 3 , CaO, Al, and AlN, which are usually incorporated in the raw materials in the combustion synthesis (CS) of α -Si 3 N 4 powders, was thoroughly investigated. The experimental results showed that these impurities seriously jeopardize the production of powders with a high content in α -Si 3 N 4 via CS. Two main mechanisms are seemingly involved in this phenomenon. First, these impurities react with SiO 2 to form eutectic compounds and with the NH 4 Cl additives to form liquid chlorides of the metals of the impurities. This liquid phase favors the formation of β -Si 3 N 4 . In the samples with Al-containing impurities, in addition to the formation of liquid phase, nuclei of β ′-SiAlON act as seeds to produce β -Si 3 N 4 crystals.

In this work, we constructively developed a highly efficient combustion synthesis (CS) strategy as a new route for the facile preparation of SiAlON based phosphors. The doping of Eu 2+ endued the Ca-α-SiAlON ceramic powders with outstanding photoluminescence behaviors of strong yellow emission peaking at around 580 nm under excitation of near-UV or blue light. Meanwhile, the as-synthesized phosphors were also featured with high phase purity, favorable uniformity and equiaxial morphology. In the CS system, the Si and Al reactants both played significant roles as comburents, which directly determined the systematic energy in the reaction. Therefore, the distinct impact of Si/Al ratio in the comburents on the phase composition, microstructure and photoluminescence properties were thoroughly studied. The experimental results demonstrated that the appropriate ratios of Si and Al in the comburents would evidently optimize the comprehensive properties of as-synthesized Ca-α-SiAlON:Eu phosphors, which showed great potential in the application of LED light source. In addition, a blue-shift phenomenon in emission spectra with the increase of Al ratio was observed and rationally revealed.

Eu-doped β-SiAlON green phosphors with different Eu 2+ -concentrations were prepared by a highly efficient combustion synthesis (CS) method. The as-synthesized β-SiAlON:Eu 2+ phosphors featured high phase purity, uniform particle size of 3–5 µm, well-crystalline morphology and outstanding luminescent behaviors. A broad green emission band centering at around 540 nm could be obtained in the emission spectra under excitation of UV or blue light. Based on the systematically investigation, the Eu 2+ -concentration had an intense impact on the phase composition, microstructure and photoluminescence properties of as-synthesized phosphors. The intensities of excitation/emission spectra were both improved with the Eu 2+ -concentration increased. However, the excessive introduction of Eu 2+ ions would inversely debase the photoluminescence behavior, possibly ascribed to the concentration-quenching effect of Eu 2+ and the distinct grain morphology. Moreover, a continuous red-shift phenomenon in emission spectra with the increase of Eu 2+ -concentration was observed and rationally uncovered.

Owing to scientific importance associated with highly reactive surfaces, the research concerning inorganic single crystals with a large percentage of exposed high-index facets has attracted much attention. In current research, α-Fe2O3 nanocubes exposed with (012) active facet was firstly synthesized via a hydrothermal method. And then a freeze-drying approach was utilized to construct nanostructured Fe2O3/graphene composite. The as-obtained composite exhibited s higher BET surface area than that of bare α-Fe2O3 nanocubes. When evaluated for lithium storage properties, the Fe2O3/graphene rendered remarkable electrochemical cycle stability and high rate performance. At the rate of 300 mA g−1, a high reversible discharge capacity of 1136 mAh g−1 was obtained up to 200 cycles. In addition, the excellent rate performance was also achieved. Excellent electrochemical properties are probably ascribed to the synergistic effect of α-Fe2O3 nanocubes and graphene sheets, as a result of smart structure design via a freeze-drying route. This strategy with merits of rational construction and scalable production could establish new perspective for diverse composites towards commercial application.

Er 3+ doped (K 0.52 Na 0.48 ) 1− x Li x NbO 3 ceramics had been prepared through a conventional solid state reaction routine and their phase structure, ferroelectric, piezoelectric, and photoluminescence properties were systematically investigated. X-ray diffraction results clearly illustrated a phase transition from the orthorhombic to coexistence and further to tetragonal phase with the increase of Li content. Via measuring the ferroelectric and piezoelectric properties of the ceramics, it found that the polymorphic phase transition (PPT) effect contributed the obvious enhancement in electrical properties of the Er 3+ doped (K 0.52 Na 0.48 ) 0.94 Li 0.06 NbO 3 ceramic which lay in the composition region of coexistence phase structure. The up-conversion photoluminescence intensity of green emission and red emission first increased as x increase from 0 to 0.06 and then decreased for x = 0.08. The most obvious enhancement in the up-conversion photoluminescence intensity was also achieved in the composition lying in the vicinity of PPT region. And the above circumstance caused the consideration that here the essence of the coexistence phase may be a phase structure with lower crystal symmetry instead of just physical combination of orthorhombic and tetragonal phase.

In this work, we purposefully reported a simple yet efficient carbothermal synthesis strategy to prepare micro-scale spherical AlN granules just by using CaF2 as promoting additive. The effects of synthesis parameters, such as CaF2 content, N-2 gas pressure, reaction temperature, upon the nitridation rate, surface morphology and particle size were comprehensively investigated. It was established that elevated N-2 gas pressure, high reaction temperature and abundant Ca-aluminates liquid synergistically promoted the formation of micro-scale spherical AlN granules. Additionally, the reduction and nitridation of intermediate Ca-aluminates played a significant role in improving the nitridation rate, increasing the particle size and forming the smooth spherical appearance. More significantly, the underlying reaction mechanism in the carbothermal synthesis of spherical AlN with CaF2 additive was also tentatively proposed. (C) 2015 Elsevier B.V. All rights reserved.

Eu-doped Ca-α-SiAlON phosphors, featuring high phase purity, uniform particle size of 3–5 μm and good luminescent properties with a yellow emission spectrum under blue light excitation, were prepared by a highly efficient combustion synthesis (CS) method. A certain amount of NaCl was applied as an innovative additive to regulate and control the properties of synthesized phosphors. Further, the effects of NaCl additive in the CS system were systematically investigated and rational proposed. It was found that the effect on accelerating nitridation and crystallization played a dominant role in the reaction as the content of NaCl was less than 6 wt%, while the effect of absorbing reaction heat through vaporization was dominant with the further-increased content of NaCl. The intensity of the emission spectrum for the sample doped with 6 wt% of NaCl was remarkably enhanced, nearly 40% more than the sample which was not NaCl-doped. Moreover, a continuous blue-shift phenomenon in emission spectra was observed with the increased content of NaCl.

In this work, Eu-doped Ca-α-SiAlON phosphors were prepared by a facile and yet efficient combustion synthesis strategy with NH 4 Cl as an exclusive additive. The as-produced Ca-α-SiAlON:Eu 2+ phosphors were featured with high purity, uniform crystal morphology of 3–5 μm in size and good luminescence properties with a yellow emission spectrum peaking at 578 nm under excitation of near-UV or blue light. Clearly, the intensity of emission spectrum for the product with 2 wt.% of NH 4 Cl increased remarkably, ∼50% higher than that of the absence of NH 4 Cl. The contradictory influences of the special additive NH 4 Cl on the photoluminescence behavior for the products were systematically investigated herein. With less than 2 wt.% of NH 4 Cl added, the effects of accelerating nitridation and crystallization dominated the combustion reaction. However, the effect of heat-absorption turned to be dominant when the content of NH 4 Cl was higher than 2 wt.%. With an increase in the content of NH 4 Cl, a continuous blue shift phenomenon in emission spectra could be observed and the concerning mechanism was uncovered.