•In Sr3Ce(PO4)3:Eu2+, the successive substitution of Sr by Ca causes microstructural transformation of PO4 tetrahedrons from disordered state to ordered state.•The disorder-to-ordered microstructural ...variation of PO4 anion-groups remotely controls Eu2+ emissions, yielding adjustable emission from yellow-green to yellow and then green emission.•This work provides a deeper understanding on how structural ordering degree affects the local structures of Eu2+ centers.
Spectrally tunable phosphors have been extensively studied for their potential applications in phosphor-converted white light-emitting diodes and display devices. Herein, we synthesize a series of color-tunable (Sr2.95-xCax)Ce(PO4)3:0.05Eu2+ (x = 0–2.95) phosphors via solid-state reaction, which are designed by using eulytite-type phosphate with different PO4 structural ordering, viz., Sr3Ce(PO4)3:Eu2+ with disordered state of PO4 tetrahedrons, and Ca3Ce(PO4)3:Eu2+ with ordered state of PO4 tetrahedrons. In Sr3Ce(PO4)3:Eu2+, the successive substitution of Sr by Ca causes microstructural transformation of PO4 tetrahedrons from disordered state to ordered state. Strikingly, the disorder-to-ordered microstructural variation of PO4 anion-groups remotely controls Eu2+ emissions, yielding adjustable emission from yellow-green to yellow and then green emission and fine tailoring of photoluminescence excitation spectra, which are demonstrated by an in-depth local structure analysis of X-ray, nuclear magnetic resonance and electron paramagnetic resonance. This work provides a deeper understanding on how structural ordering degree affects the local structures of Eu2+ centers.
The novel magnetic and structural properties of LaVO3 have been studied in a comprehensive manner using X-ray and neutron powder diffraction, thermogravimetric analysis, X-ray photoelectron ...spectroscopy, X-ray absorption spectroscopy, electrical transport, and dc magnetization. The lattice parameters have been found to be larger than previously reported, indicating the possibility of a novel phase. For vanadium ions, the valence state is found to be in accordance with the expected value (+3), the effect of larger lattice parameters is also present in the X-ray absorption spectroscopy measurement. Magnetic transition due to the antiferromagnetic ordering of the vanadium sublattice is observed at 142 K (TN). It undergoes a transition to a monoclinic crystal structure below 140 K (Tt). Negative magnetization (anomalous diamagnetism), which has been reported in earlier studies on the magnetic properties of LaVO3, is not observed in the present study. In the M − H isotherms, the ferromagnetic component of vanadium spins is absent. Below TN, the estimated magnetic structure of vanadium sublattice from powder neutron diffraction measurements is C-type antiferromagnetic, which persists in the entire low temperature region. The observed novel structural phase gives rise to pure C-type antiferromagnetic arrangement without weak ferromagnetic component. Theoretical calculations have been carried out to understand the nature of the magnetic ground state.
A2B′B″O6 perovskites: A review Vasala, Sami; Karppinen, Maarit
Progress in solid state chemistry,
20/May , Volume:
43, Issue:
1-2
Journal Article
Peer reviewed
The B-site substituted perovskite oxides A2B′B″O6 have in the recent decades gained an increasing amount of interest due to their various interesting properties and possible applications. Here we ...survey the literature for ca. one thousand A2B′B″O6 perovskite compounds. Crystal structures and the various crystal chemistry features such as ordering and valence mixing of the B cations characteristic to these compounds are reviewed, together with their electronic and magnetic properties. Most importantly, the thorough examination of the research so far carried out allows us to make predictions for a number of new A2B′B″O6 compounds yet to be synthesized and reveal exciting but not yet fully explored puzzles related to this family of functional oxide materials.
Fe-Pd based thin films with Au intermediate layer fabricated on different substrates (SiO2, SiO2/Mo, SiO2/W) were investigated at annealing temperatures up to 460°C. The samples were deposited by ...magnetron sputtering and were post-annealed in vacuum. The ongoing processes were investigated by chemical depth profiling and X-ray diffraction. The experimental results showed that the intermediate Au layer always promoted the formation of FePd3 phase which also showed L12 ordered structure except in one case with W underlayer. However, in the samples with Mo buffer but without the Au interlayer the FePd phase formed and L10 ordered phase also appeared for one stacking order. Considering the low diffusivity arising from the annealing temperature the processes were explained by grain boundary diffusion induced reaction layer formation. The formation of the ordered FePd phases was interpreted by the stress accumulation due to the different diffusivity of the components, which relaxes by the shift of the grain boundaries and the transformation of swept over regions. It was concluded, that the effect of the Au interlayer is dominant over the effect of the Mo or W buffer layers.
We have characterized the dependence of microstructure, and internal strain/stress on L10 ordering in 40nm thick FePt films with different initial stresses. The microstructural and crystallographic ...results indicate that defect annihilation and grain growth induced an increase in tensile stress of ~1GPa before extensive L10 ordering. The induced tensile stress can efficiently facilitate the nucleation of L10 phase owing to that the volume expansion of L10 ordering and atomic rearrangement neutralizes the tensile stress. If the as-deposited FePt film has a highly compressive state, the induced tensile stress will be canceled out and ordering is retarded, which results in a higher ordering temperature.
•Microstructure-stress connection in FePt films was studied.•Initial stress alters microstructure and stress evolution during annealing.•Densification induces tensile stress of ~1 GPa before extensive L10 ordering.•Induced tensile stress can efficiently facilitate the nucleation of L10 phase.•Compressively initial stress results in a higher ordering temperature .
Made to order: Aqueous dispersions of polymer-encapsulated liquid crystal (LC) droplets were synthesized with precise interfacial chemistry and sizes in the micrometer-to-sub-micrometer range. ...Size-dependent changes in LC ordering could be observed. Study of the competition between size and interfacial chemistry on LC ordering enables size-dependent properties of LC droplets to be exploited in applications such as photonics and sensing.
Platinum‐based atomically ordered alloys (i.e., intermetallic compounds) have distinct advantages over disordered solid solution counterparts in boosting the cathodic oxygen‐reduction reaction (ORR) ...in proton‐exchange‐membrane fuel cells. Nevertheless, the pivotal role of ordering degree of intermetallic catalysts in promoting ORR performance has been ignored heavily so far, probably owing to the lack of synthetic routes for controlling the ordering degree, especially for preparing highly ordered intermetallic catalysts. Herein, a family of intermetallic PtFe catalysts with similar particle size of 3–4 nm but varied ordering degree in a wide range of 10–70% are prepared. After constructing the PtFe/Pt core/shell structure with around 3 Pt‐layer skin, a positive correlation between the ordering degree of the intermetallic catalysts and their ORR activity and durability is identified. Notably, the highly ordered PtFe/Pt catalyst exhibits a high mass activity of 0.92 A mgPt−1 at 0.9 ViR‐corrected as cathode catalyst in H2–O2 fuel cell, with only 24% loss after accelerated durability tests. The ordering degree‐dependent performance can be ascribed to the compressive strain effect induced by the intermetallic PtFe core with smaller lattice parameters, and the more thermodynamically stable intermetallic structure compared to disordered alloys.
A strong and positive correlation between the ordering degree of the PtFe/Pt catalysts with their oxygen reduction reaction activity and durability is identified, which can be ascribed to the compressive strain effects and the more thermodynamically stable intermetallic structures compared to disordered alloys.
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•A controllable structural ordering is achieved in Na1+xHf2−xScx(PO4)3:Eu series.•The PLQY values for all scandium-involved analogues are all higher than 90%.•Structural ordering ...guarantees the most thermally stable luminescence in NHS0.3:Eu.
Exploring NASICON-type materials emerges the fully ordered NaHf2(PO4)3 compound. Its cation/vacancy distribution forms an absolutely structural ordering three-dimensional arrangement. Further preparing a solid solution following Na1+xHf2−xScx(PO4)3:Eu (NHSx:Eu; 0.0 ≤ x ≤ 1.6) confirms all compounds are isostructural. Densely atomic-connected framework guarantees the efficient blue emission, which yields > 90% photoluminescence quantum yield (PLQY) for all scandium-substituted analogues, yet the existence of heavy amount of luminescence killer (Eu3+) limits the performance of NaHf2(PO4)3:Eu as a luminescent phosphor. Moreover, a controllable structural ordering/disordering is achieved by varying x value, which is confirmed by Raman and 31P MAS NMR spectra. The structural ordering/disordering is crucial in determining structural rigidity. Consequently, despite the voids in the framework filled with sodium ions as x increases has positive contribution to the structural robustness, cation/vacancy ordered form still builds the most rigid structure for NHS0.3, as established by the NHS0.3 composition possessing the highest Debye temperature within the scandium-involved analogues, which are extracted experimentally by the low temperature specific heat measurements. As such, NHS0.3:Eu has the best thermal stability across the x range, which keeps 90% of integrated intensity up to 203 ℃ compared with room temperature value. This work provides insight into the structural specialty of NASICON structure.
Crowdfunding: Tapping the right crowd Belleflamme, Paul; Lambert, Thomas; Schwienbacher, Armin
Journal of business venturing,
09/2014, Volume:
29, Issue:
5
Journal Article
Peer reviewed
Open access
With crowdfunding, an entrepreneur raises external financing from a large audience (the “crowd”), in which each individual provides a very small amount, instead of soliciting a small group of ...sophisticated investors. This article compares two forms of crowdfunding: entrepreneurs solicit individuals either to pre-order the product or to advance a fixed amount of money in exchange for a share of future profits (or equity). In either case, we assume that “crowdfunders” enjoy “community benefits” that increase their utility. Using a unified model, we show that the entrepreneur prefers pre-ordering if the initial capital requirement is relatively small compared with market size and prefers profit sharing otherwise. Our conclusions have implications for managerial decisions in the early development stage of firms, when the entrepreneur needs to build a community of individuals with whom he or she must interact. We also offer extensions on the impact of quality uncertainty and information asymmetry.
•Two forms of crowdfunding are compared: pre-ordering vs. profit sharing.•Profit sharing is optimal for entrepreneurs with large capital requirements.•Building a community that supports the entrepreneur is crucial for crowdfunding to be a viable funding mechanism.
This work presents an extensive investigation of the Pickering stabilization of liquid crystal (LC)-in-water emulsions using soft nanometer-sized colloidal poly(N-isopropylacrylamide) (PNIPAM) ...microgel particles and the responsivity of the PNIPAM microgel-stabilized Pickering LC droplet-based assembly towards amphiphilic analytes. The evolution of size and stability of LC droplets with microgel concentration are found to be dependent on the emulsifier-regime. Despite microgel coating, the LC-water interface remains accessible to model analytes such as anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB). The analytes can pass through the interfacial pores and/or meshes of porous microgels to induce a bipolar-to-radial ordering transition within the droplets. The dose-response behaviour is largely influenced by the initial microgel concentration, type of analytes and interfacial layer (charge), and the number of droplets exposed to the analytes. The PNIPAM microgel-coated LC droplets notably exhibited enhanced sensitivity under conditions promoting electrostatic attractive interactions between the interfacial microgel layer and analytes. Overall, the results highlight the potential of Pickering LC-in-water emulsions for reliable and quantitative analysis of aqueous analytes, thus opening up new avenues toward the development of droplet-based optical sensors.
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