Interlayer Engineering of VS2 Nanosheets via In Situ Aniline Intercalative Polymerization toward Long-Cycling Magnesium-Ion Batteries.

Rechargeable magnesium batteries (RMBs) show great potential in large-scale energy storage systems, due to Mg2+ with high polarity leading to strong interactions within the cathode lattice, and the limited discovery of functional cathode materials with rapid kinetics of Mg2+ diffusion and desirable cyclability retards their development. Herein, we innovatively report the confined synthesis of VS2/polyaniline (VS2/PANI) hybrid nanosheets. The VS2/PANI hybrids with expanded interlayer spacing are successfully prepared through the exfoliation of VS2 and in situ polymerization between VS2 nanosheets and aniline. The intercalated PANI increases the interlayer spacing of VS2 from 0.57 to 0.95 nm and improves its electronic conductivity, leading to rapid Mg-ion diffusivity of 10-10-10-12 cm2 s-1. Besides, the PANI sandwiched between layers of VS2 is conducive to maintaining the structural integrity of electrode materials. Benefiting from the above advantages, the VS2/PANI-1 hybrids present remarkable performance for Mg2+ storage, showing high reversible discharge capacity (245 mA h g-1 at 100 mA g-1) and impressive long lifespan (91 mA h g-1 after 2000 cycles at 500 mA g-1). This work provides new perspectives for designing high-performance cathode materials based on layered materials for RMBs.

The in situ phosphorization inducing oxygen vacancies in the core-shell structured NiFe oxides boosts the electrocatalytic activity for the oxygen evolution reaction.

Transition metal-based oxides have been reported as an important family of electrocatalysts for water splitting owing to their possible large-scale applications that are highly desirable for the hydrogen generation industry. Herein, we report a facile method for the preparation of phosphate-decorated NiFe oxides on nickel foam as efficient oxygen evolution reaction (OER) electrocatalysts for water oxidation. The OER electrocatalysts were developed through the pyrolysis of MIL(Fe) metal-organic frameworks (MOFs), which were modified with Ni and P species. It was found that the formation of NiO on the Fe2O3 surface (NiO@Fe2O3) can enrich electrocatalytic active sites for the OER. Meanwhile, the incorporation of P into NiO@Fe2O3 (Px-NiO@Fe2O3) creates abundant oxygen vacancies, which facilitates the surface charge transfer for OER electrocatalysis. Benefiting from the structure and composition advantages, P2.0-NiO@Fe2O3/NF exhibits the best performance for OER electrocatalysis among other prepared electrocatalysts, with an overpotential of 208 mV at the OER current density of 10 mA cm-2 and a small Tafel slope of 69.64 mV dec-1 in 1 M KOH solution. Additionally, P2.0-NiO@Fe2O3/NF shows an outstanding durability for the OER electrocatalysis, maintaining the OER current density above 20 mA cm-2 for more than 100 h.

White-emitting orthosilicate phosphor α-Sr2SiO4:Ce3+/Eu2+/K+: a bimodal temperature sensor with excellent optical thermometric sensitivity.

Non-contact temperature sensors with low cost, high reliability and high sensitivity have attracted increasing research interest in recent years. In this study, we synthesized a bimodal optical temperature sensor Sr2SiO4:Ce3+/Eu2+/K+ with excellent thermometric sensitivity through a high-temperature solid-state reaction method. In the matrix of α-Sr2SiO4, Ce3+ luminescence exhibits excellent thermal stability (∼129.1%@250 °C), while Eu2+ shows strong thermal quenching (∼21.7%@250 °C), leading to a significant change in the fluorescence intensity ratio (FIR) of Ce3+ (437 nm) and Eu2+ (550 nm) as a function of temperature. This feature enables the phosphor exhibiting outstanding sensitivity in the temperature range of 298-523 K. To be exact, it demonstrates a maximal relative sensitivity of 0.93% K-1 at 348 K. Its absolute sensitivity linearly increases and reaches 3.46% K-1 at 523 K. Besides, it has a large chromaticity shift (ΔE = 228 × 10-3 in 298-523 K) against temperature, making the temperature change visible to the naked eye. We first demonstrate a CIE chromaticity coordinate technique for temperature sensing with high accuracy and good sensitivity by using the function of x or (x2 + y2)0.5 against T. These unique optical thermometric features allow Sr2SiO4:Ce3+/Eu2+/K+ to serve as an accurate and reliable thermometer probe candidate for temperature sensing applications.

Investigation of the Solid-Solution Limit, Crystal Structure, and Thermal Quenching Mitigation of Sr-Substituted Rb2CaP2O7:Eu2+ Phosphors for White LED Applications.

Rb2CaP2O7:Eu2+ is a bright reddish-orange-emitting phosphor, but its luminescence thermal stability is poor. In this study, we investigated the solid-solution limit and thermal quenching mitigation of Rb2CaP2O7:Eu2+ phosphors by cation substitution with Sr2+ and revisited their crystal structure. First, we carefully investigated the solid solution limit of Sr in the structure of Rb2CaP2O7. The results show that up to 80% of Ca can be substituted by Sr, whereas Ca hardly resides in the structure of Rb2SrP2O7. Consequently, the photoluminescence was fine-tuned from reddish-orange (612 nm) to yellow (580 nm) light emission by increasing the Sr2+ concentration in the solid-solution phosphors Rb2Sr1-xCaxP2O7:Eu2+ under excitation at 342 nm. The mechanism for the blue shift of the emission spectrum was discussed. With the associated modification of the local environment of the activator (as reflected by the changes in the effective coordination number, average bond length, distortion index, and quadratic elongation), the luminescence thermal quenching issue of Rb2CaP2O7:Eu2+ was mitigated by substituting 20% Sr into the Ca site (Rb2Ca0.8Sr0.2P2O7:Eu2+). The integrated intensity of bright orange-emitting Rb2Ca0.8Sr0.2P2O7:Eu2+ (603 nm) at 150 °C retained 53% of its initial value, 1.64 times that of Rb2CaP2O7:Eu2+ (32.3%). Such an enhancement could be attributed to the improved rigidity of the crystal structure due to the local structure modification as evidenced by Rietveld refinement. The cation substitution is an effective approach for mitigating the thermal quenching issue of phosphors.

Electrochemical incorporation of heteroatom into surface reconstruction induced Ni vacancy of NixO nanosheet for enhanced water oxidation.

Surface reconstruction of non-oxide oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve their catalytic performances. However, further modification of the reconstructed active surfaces for better catalytic performances has not been reported. In this work, NiSe nanorods are prepared on nickel foam (NiSe@NF) as the pre-catalyst for electrochemical OER. It is revealed that non-stoichiometric NiO nanosheets with abundant Ni vacancies (NixO) are formed on the surfaces of NiSe nanorods (NixO/NiSe@NF) via in-situ electrochemical oxidation. Furthermore, the OER performances are obviously improved after heteroatom Fe is incorporated electrochemically into NixO nanosheets ((FeNi)O/NiSe@NF). For OER to have a current density of 20 mA cm-2 in 1 M KOH solution, the as-prepared (FeNi)O/NiSe@NF electrode only needs an overpotential of 268 mV. Density functional theory (DFT) calculations reveal that the formation of Ni vacancy can increase the free energy of *OH. More importantly, the incorporation of heteroatom Fe into Ni vacancy can significantly decrease the free energy of *O, which enables Fe-NiO to have the lowest theoretical overpotential for OER in this work. The present work provides a facile and universal strategy to modify the reconstructed active oxides' surfaces for higher electrocatalytic performances.

ß-Si3N4 Microcrystals Prepared by Carbothermal Reduction-Nitridation of Quartz.

Single phase ß-Si3N4 with microcrystals was synthesized via carbothermal reduction-nitridation (CRN) of quartz and carbon coke powder as starting materials. The effects of reaction parameters, i.e., heating temperature, holding time, C/SiO2 ratio, Fe2O3 additive and ß-Si3N4 seeds on the phase transformation and morphology of products were investigated and discussed. Rather than receiving a mixture of both α- and ß- phases of Si3N4 in the products, we synthesized powders of ß-Si3N4 single polymorph in this work. The mechanism for the CRN synthesis of ß-Si3N4 from quartz and the formation mechanism of Fe3Si droplets were discussed. We also firstly reported the formation of Fe3Si Archimedean solids from a CRN process where Fe2O3 was introduced as additive. Comparing to the gear-like short columnar morphology observed in samples without ß-Si3N4 seeding, the addition of ß-Si3N4 seeds led to an elongated morphology of final products and much finer widths. In addition, the ß-Si3N4 microcrystals exhibited a violet‒blue spectral emission range, which could be highly valuable for their future potential optoelectronic applications.

"114"-Type Nitrides LnAl(Si4-x Alx )N7 Oδ with Unusual [AlN6 ] Octahedral Coordination.

Aluminum-nitrogen six-fold octahedral coordination, [AlN6 ], is unusual and has only been seen in the high-pressure rocksalt-type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si4-x Alx )N7 Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6 ] coordination prepared via non-high-pressure synthesis. Structure refinements of neutron powder diffraction and single-crystal X-ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P63 mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4 ] tetrahedra. Solid-state NMR data of high-purity La-114 powders confirm the unusual [AlN6 ] coordination. These compounds are the first examples of the "33-114" sub-type in the "114" family. The additional site for over-stoichiometric oxygen in the structure of 114-type compounds was also identified.

Correction: ß-Sialon nanowires, nanobelts and hierarchical nanostructures: morphology control, growth mechanism and cathodoluminescence properties.

Correction for 'ß-Sialon nanowires, nanobelts and hierarchical nanostructures: morphology control, growth mechanism and cathodoluminescence properties' by Juntong Huang, et al., Nanoscale, 2014, 6, 424-432.

Trace phase formation, crystallization kinetics and crystallographic evolution of a lithium disilicate glass probed by synchrotron XRD technique.

X-ray diffraction technique using a laboratory radiation has generally shown limitation in detectability. In this work, we investigated the in situ high-temperature crystallization of a lithium disilicate glass-ceramic in the SiO2-Li2O-CaO-P2O5-ZrO2 system with the aid of synchrotron radiation. The formation of lithium metasilicate and other intermediate phases in trace amount was successfully observed by synchrotron X-ray diffraction (SXRD). The crystallization mechanism in this glass was thus intrinsically revised to be the co-nucleation of lithium metasilicate and disilicate, instead of the nucleation of lithium disilicate only. The phase content, crystallite size and crystallographic evolutions of Li2Si2O5 in the glass-ceramic as a function of annealing temperature were studied by performing Rietveld refinements. It is found that the growth of Li2Si2O5 is constrained by Li2SiO3 phase at 580-700°C. The relationship between the crystallographic evolution and phase transition was discussed, suggesting a common phenomenon of structural response of Li2Si2O5 along its c axis to other silicon-related phases during glass crystallization.

Cation substitution dependent bimodal photoluminescence in whitlockite structural Ca(3-x)Sr(x)(PO4)2:Eu(2+) (0 ≤ x ≤ 2) solid solution phosphors.

Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca3-xSrx(PO4)2:Eu(2+) (0 ≤ x ≤ 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ≤ x ≤ 2. In addition to the emission band peak at 416 nm in Ca3(PO4)2:Eu(2+), the substitution of Ca(2+) by Sr(2+) induced the emerging broad-band peak at 493-532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of x in the samples with 0.75 ≤ x ≤ 2.00. The two emission bands could be related to the EuOn-Ca9 and EuOn-Ca9-xSrx emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks.

New yellow-emitting Whitlockite-type structure Sr(1.75)Ca(1.25)(PO4)2:Eu(2+) phosphor for near-UV pumped white light-emitting devices.

New compound discovery is of interest in the field of inorganic solid-state chemistry. In this work, a whitlockite-type structure Sr1.75Ca1.25(PO4)2 newly found by composition design in the Sr3(PO4)2-Ca3(PO4)2 join was reported. Crystal structure and luminescence properties of Sr1.75Ca1.25(PO4)2:Eu(2+) were investigated, and the yellow-emitting phosphor was further employed in fabricating near-ultraviolet-pumped white light-emitting diodes (w-LEDs). The structure and crystallographic site occupancy of Eu(2+) in the host were identified via X-ray powder diffraction refinement using Rietveld method. The Sr1.75Ca1.25(PO4)2:Eu(2+) phosphors absorb in the UV-vis spectral region of 250-430 nm and exhibit an intense asymmetric broadband emission peaking at 518 nm under λex = 365 nm which is ascribed to the 5d-4f allowed transition of Eu(2+). The luminescence properties and mechanism are also investigated as a function of Eu(2+) concentration. A white LED device which is obtained by combining a 370 nm UV chip with commercial blue phosphor and the present yellow phosphor has been fabricated and exhibit good application properties.

ß-Sialon nanowires, nanobelts and hierarchical nanostructures: morphology control, growth mechanism and cathodoluminescence properties.

Morphology control of one dimension (1D) nanomaterials is a pivotal issue in the field of nanoscience research to exploit their novel properties. Herein, we report the morphology controlled synthesis of 1D ß-Sialon nanowires, nanobelts and hierarchical nanostructures via a thermal-chemical vapour deposition process using an appropriately selected catalyst and optimized temperature schedule. Vapour-solid (VS), a combination of vapour-liquid-solid (VLS)-based and VS-tip, and a combination of VS for one-generation nanowires with nucleation, growth and coalescence of two-generation nanobranches (NGCB) are used to explain the growth of ß-Sialon nanowires, nanobelts and hierarchical nanostructures, respectively. Cathodoluminescence measurements show that the individual ß-Sialon 1D nanostructures with different morphologies have different luminescent properties. All nanostructures exhibit two distinct emission peaks, the violet/blue emission centered at ~390 nm (3.18 eV), attributable to the near band edge (NBE) emission, and the red emission centered at ~728 nm (1.70 eV), assigned to the deep level (DL) emission. However, the DL emission is the ruling emission in the case of an individual ß-Sialon nanowire, whereas the NBE emission becomes dominant in the case of an individual nanobelt as well as a hierarchical nanostructure due to the size and surface effects. The as-synthesized ß-Sialon with controlled nanostructures and various morphologies can find potential applications in future nanodevices with tailorable or tunable photoelectric properties.

In situ high-temperature crystallographic evolution of a nonstoichiometric Li2O·2SiO2 glass.

In this work, the high-temperature crystallographic evolution of crystalline phases in a complex lithium disilicate glass was investigated using synchrotron X-ray powder diffraction. The lattice parameters and unit cell volume of Li2SiO3 (LS), Li2Si2O5 (LS2), Li3PO4 (LP), and ZrO2 as a function of temperature were determined upon heating. It is found that the lattice parameter c of LS2 shows a "V"-shaped trend during heating. The crystallographic evolution of the LS2 phase has a close correlation with the LS phase, indicating the mutual interaction between LS and LS2 phases along the c axis during the nucleation/crystallization process. The phase evolution processes were different upon heating and cooling, and the unit cell volume of both LS and LP phases demonstrated different change rates. In this glass system, no LS2 was detected during cooling and the main phases formed during cooling process were LP, LS, ß-cristobalite, and ß-quartz. Interestingly, there were two forms of ß-quartz with slightly different lattice constants, and the silica phases showed a near-zero expansion behavior. The crystallographic evolution mechanism is discussed.

Crystal structure of NdSi(6-z)Al(1+z)O(z)N(10-z) (z = 0.4) determined by single-crystal X-ray diffraction.

Single crystals of JEM-phase NdSi(6-z)Al(1+z)O(z)N(10-z) were successfully prepared from starting powders of Si3N4, AlN and Nd2O3 at 1700 °C for 3 h under nitrogen atmosphere. The z value of Nd-doped JEM-phase was determined to be 0.4 via determination of oxygen and nitrogen by elemental analysis. This result may be beneficial for overcoming the difficulty on preparation of single-phase JEM-phase Sialon materials and further characterization on their properties. The detailed crystal structure of Nd-Sialon was solved on the basis of single-crystal X-ray diffraction data for the first time. The space group is Pbcn (no. 60); a = 9.3060(6) Å, b = 9.7224(6) Å, c = 8.8777(5) Å; Z = 4; V = 803.22(8) ų; D(c) = 3.971 g cm⁻³; R1 = 0.0297 and wR2 = 0.0739 for all reflections refined against F², with GooF value of 1.031.