Journal of Solid State Chemistry最新文献

Mn⁴⁺-doped fluoride red phosphors have been widely used in warm WLEDs, but the preparation of such phosphor requires the use of a large amount of HF as a fluorine source and an acidic environment. How to reduce the excessive use of highly toxic HF in the preparation process and achieve green synthesis has become a hot research topic. Therefore, a simple green synthesis strategy is proposed in this work to synthesize a series of red-emitting phosphors Na₃AlF₆:Mn⁴⁺. The highly toxic HF solution is replaced by using a low toxicity reaction system (HCl/HNO₃ + NH₄F), which reduces the direct use of HF. X-ray powder diffraction, energy-dispersive X-ray spectrometer and scanning electron microscope are employed to determine the crystal structure, composition and morphology of all samples. Optical properties are characterized using excitation spectra, emission spectra and fluorescence lifetime curves. The calculation results indicate that the red-light has low correlated color temperature and the excellent color purity, and Na₃AlF₆ host can provide a strong crystal field environment for Mn⁴⁺. In addition, different aluminum sources and Mn⁴⁺ doping concentrations are used to explore the optimal preparation condition. The mechanisms of concentration quenching and thermal quenching have also been systematically explored. The stabilities of red-light emission intensity and color are investigated under the high temperature. The integral PL intensity at 423 K is 47 % of the initial value at 298 K. The activation energy, the chromaticity shift and the chromaticity coordinate variation are also systematically calculated. More importantly, a high-performance warm WLED with low correlated color temperature (CCT = 3296 K) and high color rendering index (R_a = 94.7) is achieved by using Na₃AlF₆:Mn⁴⁺ as a red-emitting material. Not only that, the warm WLED exhibits strong output stability under high driving current. The discovery of this work provides a comprehensive understanding for the rational design of high-performance Mn⁴⁺-activated fluoride red phosphors via a simple green synthesis strategy.

β-ketoenamine-based COFs are widely investigated due to their high stability, good crystallinity and tunable skeleton structures. Nitrogen doping is one of the effective ways to enhance the catalytic activity of COFs. Herein, N-doping of β-ketoenamine-based (0N-TP-COF, 1N-TP-COF, 2N-TP-COF) COFs were successfully constructed by the Schiff base condensation reaction between 1,3,5-tiformylphloroglucinol (TP) and p-phenylenediamine containing different numbers of nitrogen atoms. Studies showed that the as-prepared COFs exhibited more suitable electronic structure and more electron-rich active sites with the increasing of N atoms. Furthermore, the photocatalytic performance of 4-formylphenylboronic acid transformation was 0N-TP-COF (99 %, 48 h) < 1N-TP-COF (99 %, 32 h) < 2N-TP-COF (99 %, 16 h), and the photocatalytic performance of benzylamine coupling was 0N-TP-COF (99 %, 16 h) < 1N-TP-COF (99 %, 3.5 h) <2N-TP-COF (99 %, 1.5 h), respectively. Note that all N-doping COFs have excellent catalytic activity as well as stability, and 2N-TP-COF exhibits the highest catalytic activity. This work demonstrates that doping of nitrogen atoms is an effective way to enhance photocatalytic performance.

In this study, we present the crystallographic and magnetic characterization of a new intermetallic compound Sm₂PdGe_3, which was synthetized by a two stage method employing an eutectic alloy. The investigations carried out exhibited, that Sm₂PdGe₃ crystallize in AlB₂-type structure with lattice parameters a = 4.2189(1) Å and c = 4.1031(2) Å. This compound can be classified as a cluster-glass with a spin freezing temperature T_f = 10.5 K. Furthermore, there were carried out the analysis of the role of the rare earth (RE) elements on the structural parameters of RE₂PdGe₃ and draw a correlation between the RE radius and the unit cell parameters. We show that a deviation from the ideal 1:3 Pd:Ge ratio is necessary to synthesize RE₂PdGe₃ with smaller RE elements.

Z-Scheme heterojunction photocatalysts can effectively suppress the recombination of charge carriers while maintaining high redox capacity. In this study, ZnTe/WO₃ (ZW) Z-scheme heterojunction photocatalysts were synthesized using a hydrothermal method, and a series of photocatalytic materials were prepared for the simultaneous removal of tetracycline (TC) and Cu(II) from water. The physicochemical and photoelectrochemical properties of the catalytic materials were characterized through various methods, including SEM, XRD, XPS, and others. The experimental results indicate that the ZW-10 % composite material exhibits the most significant removal efficiency for pollutants. Within 150 min of visible light irradiation, the removal rates for TC and Cu(II) reach 73.8 % and 73.3 %, respectively, representing a substantial improvement compared to individual ZnTe and WO₃. Free radical capture experiments and electron spin resonance analysis reveal that ·O₂⁻ and ·OH are the key reactive species responsible for TC oxidation, while electrons (e⁻) dominate the reduction of Cu(II).

Cubic antiferromagnet Cu₃TeO₆ demonstrates interesting magnetic properties. Aimed at modification of them, we tried multiple ionic substitutions in its structure. However, single-phase materials could only be prepared with large fraction of the Jahn-Teller ions (Cu²⁺ and Mn³⁺), although formally isostructural bixbyites R₂O₃ (R₄O₆) with R = Sc, In, Tl, Sm…Lu exist with no Jahn-Teller ions. Moreover, ions having highest octahedral crystal field stabilization energy (Ni²⁺ and Cr³⁺) were found least tolerable. This points to Cu₃TeO₆ as a separate structure type, distinct from classical bixbyites. We report crystal structure, magnetic and thermodynamic properties of a rare single-phase multicomponent preparation, Cu_3/2Mn_1/2Co_1/2Fe_1/2SbO₆. The dc magnetic studies show that the formation of the ground spin-cluster state at T = 18 K is preceded by a broad anomaly at ∼122 K. Both specific heat and ac susceptibility data rule out the long-range magnetic ordering, in contrast to closely related Cu₂MSbO₆ (M = Mn or Fe).

In this study, we used a coprecipitation method followed by calcination at 500 °C to synthesize undoped and Al³⁺-doped Co₃O₄ nanoparticles with different aluminum fractions (x = Al/(Co + Al) = 1/60, 1/30, 1/15, 1/75, 1/6 and 1/5). An addition of Al³⁺ ions led to a decrease in the average crystallite size from 29 to 11 nm, and growth of the specific surface area from 28 to 91 m²/g. TEM images indicated round and platelet shapes of the nanoparticles. According to HAADF-STEM combined with EDS elemental mapping, the platelet shape particles are Al³⁺-enriched, while the round shape particles are Al³⁺-depleted. The origin of Al³⁺ distribution over the oxide volume is conditioned by the state of the hydroxide precursor. It was shown by XRD that the coprecipitation yielded homogeneous hydroxides only for Al fractions x = 0 and x = 1/5. For the intermediate compositions, the precursors represent a mixture of Co₆(CO₃)₂(OH)₈*H₂O and Co_0.8Al_0.2(OH)₂(CO₃)_0.1*nH₂O. On the TPR-H₂ profiles, reduction peaks for three (Co,Al)₃O₄ oxides differing in the Al³⁺ concentration (y) can be found. Two of these oxides with y = 0 and y = 0.2 are formed from different hydroxides, and third one with y ∼0.05 is the result of their mutual interaction. In situ XRD allowed us to interpret the TPR peaks correctly and showed that the reduction of all the oxides occurs in two steps. In the first step, Co³⁺ → Co²⁺, and (Co_1-yAl_y)₃O₄ oxides transform to (Co,Al)O. In the second step, Co²⁺ → Co⁰, and (Co,Al)O is reduced into metallic cobalt. In undoped Co₃O₄, Co³⁺ → Co²⁺ and Co²⁺ → Co⁰ reduction steps occur at T₁ = 280 and T₂ = 325 °C, respectively. For Al-depleted (Co_1-yAl_y)₃O₄ (y ∼ 0.05 in the interior of particles), both reduction steps shift toward higher temperatures T₁ = 305 and T₂ = 405 °C, respectively. The reduction of Al-enriched (Co_0.8Al_0.2)₃O₄ is more difficult; first and second reduction steps occur at T₁ = 345 and T₂ = 610−690 °C. Therefore, Al³⁺ ions have a little effect on the first step and very significantly influence the second one. Additionally, it was shown by TEM that after the reduction at 700 °C metallic cobalt particles were surrounded by the Al-enriched oxide shell. Apparently, that is why the addition of even a small amount of Al³⁺ ions prevents a quick sintering of metallic cobalt observed for pure Co₃O₄.

Mixed-valence Cs₂Au^IAu^IIIX₆ (X = I, Br, Cl) double perovskites (DPs) exhibit high chemical stability and tunable optical band gaps, which renders their potential for photovoltaics. As an alternative, the suitability of novel mixed-valence mixed-halide perovskites for solar cell devices is studied herein. The cation-anion dual-doping strategy is utilized for Cs₂Au^IAu^IIIX₆, where the Au^I cations are substituted by the Ag^I cations and the anions are doped by different proportions of halide anions. The class of mixed-valence mixed-halide perovskites Cs₂Ag^IAu^IIIX₄Y₂ and Cs₂Ag^IAu^IIIX₂Y₄ (X = I or Br; X = Br or Cl) is comprehensively investigated with regard to their optoelectronic properties and structural stability. Apart from good thermodynamic and mechanical stability, Cs₂Ag^IAu^IIII₄X₂ (X = Br, Cl) and Cs₂Ag^IAu^IIIBr₄Cl₂ exhibit optimum band gaps within 1.2–1.4 eV and have low reduced effective masses (<0.25 m₀) and small exciton binding energies (<110 meV). Additionally, three alternative mixed-halide DPs show high visible-light absorption. Ultimately, the simulated maximum efficiency is within 29–31 % for three novel mixed-halide DPs. Considering structural stability and optoelectronic properties, Cs₂Ag^IAu^IIII₄Br₂ is expected to be an appropriate candidate for high-efficiency thin-film solar cells. The theoretical prediction of mixed-valence mixed-halide DPs can provide an attractive route to discover high-performance photovoltaic materials.

An alkaline-stable Zr-based material, PCN-777, has been elected and solvothermally prepared by reacting ZrOCl₂ with the tripodal linker 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoate (H₃TATB). This powder material exhibits an irregular octahedron motif, providing good stability and high-power density when it is employed as electrode material for supercapacitors (SCs). The results indicate that the specific capacity, under a three-electrode configuration, is 291.9 C g⁻¹ at a current density of 1.5 A g⁻¹ obtained from the chronopotentiometry charge-discharge test. Assembled into a two-electrode system with activated carbon (AC) negative, the corresponding battery-supercapacitor device denoted as PCN-777//AC delivers a specific capacitance of 48.72 F g⁻¹ at the constant current-density value of 0.5 A g⁻¹. Besides, this device delivered a maximum energy density of 17.3 Wh kg⁻¹ within the power-density value of 399 W kg⁻¹, an excellent alkaline-endurance life during 2000 unceasing cycles and practical applications in powering LEDs, suggesting the potential practicality under strong alkaline surroundings. Furthermore, the structural alteration before and after long-term cycling has also been investigated.