Solid State Sciences最新文献

In layered perovskites with the Carpy-Galy structural type, similar structural phase transitions occur under high pressure. These structural changes, which are crucial for the pressure-induced phase transition in layered perovskite, were analyzed based on experimental X-ray diffraction data. The tilting of the Ti-O₆ octahedra and the distortion of the arrangement of rare-earth atoms were studied in detail. Changes in these structural features in layered perovskite serve as common indicators of the phase transition to the monoclinic phase that occurs under high pressure application.

The conversion of CO₂ into fuel using photocatalytic technology is critical in reducing greenhouse gas emissions and addressing the energy issue. In this paper, type II heterojunctions of 2D/2D BiOIO₃/Bi-MOF were built using the solvothermal approach. The materials were characterized utilizing methods such as XRD, SEM, TEM, XPS, UV–vis diffuse reflection, and an electrochemical workstation. Under 300 W Xenon lamp irradiation, BiOIO₃/Bi-MOF-30 (BOIOB-30) produced 21.26 μmol/g/h of CO, 1.95 times greater than pure BiOIO₃. This improvement is related to the alteration of BiOIO₃ with lamellar Bi-MOF, which provides more reactive sites and significantly increases the composite's photocatalytic activity.

In this study, Na_1/3Cd_1/3(Bi_1-xY_x)_1/3Cu₃Ti₄O₁₂ (NCBYCTO, x = 0−0.20) ceramics were successfully prepared via solid state method. Their microstructure along with the optical, dielectric, and non-Ohmic properties were investigated systemically. It was shown that Y³⁺ doping caused the decrease in cation vacancy concentration and the increase in optical energy band. With the increase of Y³⁺ content, ceramics exhibited a more stable structure, while their average grain size increased from 6.80 μm to 9.12 μm and then decreased to 2.17 μm with the dopant amount. The relative density increased from 94.7 % for the undoped specimen to 95.6 % for the specimen with x = 0.20. The giant dielectric constant (ɛ′ = 44200) at a relatively low dielectric loss (tanδ = 0.048) at 10 kHz was obtained in the specimen with x = 0.08, being more than three times that of undoped sample and demonstrating the outstanding frequency stability in the range of 40−10⁶ Hz. The giant dielectric constant below 10⁶ Hz originated from Maxwell–Wagner relaxation related to the insulating grain boundaries (GBs) and followed the internal barrier layer capacitor model. Besides that, Y³⁺ doping improved the nonlinearity properties of NCBYCTO ceramics. The specimen with x = 0.20 had the largest nonlinearity coefficient α (∼9.60) and breakdown field strength E_b (∼7.15 kV/cm). At last, the nonlinear J-E characteristics were closely related to the GB conductivity activation energy.

Photocatalysis is a promising strategy for the production of H₂O₂, but the promotion of 2e⁻ ORR selectivity remains a challenging goal in this field. Herein, Potassium (K⁺), cyano groups (-C≡N) and porous ultrathin structures were introduced into g-C₃N₄ simultaneously by the hyphenated technique of gas template method and molten salt-assisted method. The K⁺ and –C≡N can broaden the light absorption range, improve the reduction ability and promote electron transfer of the catalyst. Additionally, the presence of a permeable ultrathin structure plays a crucial role in improving the specificity of the 2e⁻ oxygen reduction reaction (ORR). Benefiting from the multiple advantages, the H₂O₂ yield of K⁺ intercalated cyano-rich porous ultrathin g-C₃N₄ (KUCN) reached 781.39 μM with an extraordinary 2e⁻ ORR selectivity of 94.5% (0.30 V vs. RHE). Overall, this study presents a practical approach for designing catalysts based on g-C₃N₄ that exhibit a high selectivity for the 2e⁻ ORR reaction.

The aim of this work is to establish the relationship between the electrochemical performance of the Pr_1.6Cа_0.4Ni_0.6Cu_0.4O_4+δ-based electrodes and the properties of the electrode powders, conditioned by their synthesis history, as well as the electrode design and the sintering conditions of the electrode layers. The Pr_1.6Cа_0.4Ni_0.6Cu_0.4O_4+δ (PCNCO) powders are synthesized by combustion of salt compositions using different fuels: glycine, polyvinyl alcohol and citric acid. The influence of the composition of the redox mixture on the synthesis process, the phase composition of the obtained powders and their properties have been studied. The microstructure of the PCNCO electrodes formed from the powders with different dispersions is studied by electron microscopy. The electrochemical performance of the electrodes in contact with the Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte is studied by impedance spectroscopy. Based on the correlations established between the chemical stability and dispersion of the powders and the microstructure and polarization resistance of the corresponding electrodes, the optimal parameters for the synthesis of the PCNCO complex oxide for the use as a cathode material have been determined. The lowest polarization resistance equal to 0.38 Ω cm² at 700 °C is obtained for the bilayer electrode with the PCNCO functional layer synthesized by the citrate-nitrate combustion and sintered at 1050 °C, and the LaNi_0.6Fe_0.4O_3–δ oxide collector sintered at 900 °C. The developed synthesis procedure and electrode design can be recommended as promising for the fabrication of air electrodes in the intermediate-temperature electrochemical devices.

Sulfide (ZnS)(Ag₂S)_x heteronanostructures of various composition were obtained by co-deposition from water colloidal solutions of silver and zinc nitrates using sodium sulfide as a sulfidizer and sodium citrate as a stabilizer. The formation of (ZnS)(Ag₂S)_x heteronanostructures was confirmed using the XRD, HAADF-STEM, SEM, EDX and Raman spectroscopy. The size of ZnS and Ag₂S nanoparticles in heteronanostructures (ZnS)(Ag₂S)_x with x ≤ 0.01 is 2–4 and no more than 3 nm, respectively. Raman spectroscopy showed that addition of silver sulfide nanoparticles into (ZnS)(Ag₂S)_x heteronanostructures leads to Ag₂S deposition onto the surface of ZnS nanoparticles. Doping ZnS with only 1 mol.% of colloidal Ag₂S nanoparticles is sufficient to produce a silver sulfide shell on the surface of ZnS nanoparticles.

Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ coatings for application in photocatalytic degradation of methyl orange were prepared by plasma electrolytic oxidation of tantalum in an alkaline electrolyte with different concentrations of CdS, ZnO, and Dy₂O₃ particles up to 2.0 g/L. The coatings were characterized by SEM/EDS, XRD, Raman spectroscopy, DRS and photoluminescence spectroscopy. The morphology, thickness, phase structure and absorption properties of all coatings are almost identical and independent of the content of CdS, ZnO, and Dy₂O₃ embedded in Ta₂O₅ coatings. The orthorhombic and monoclinic phases of Ta₂O₅ are the main constituents of the coatings. Due to the low content of embedded CdS, ZnO, and Dy₂O₃ in Ta₂O₅ coatings, they exhibit high absorption in the middle ultraviolet region, which is characteristic of Ta₂O₅. The photocatalytic activity (PA) of Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ is higher than that of pure Ta₂O₅ and depends on the amount of CdS, ZnO, and Dy₂O₃ in the electrolyte, respectively. The highest PA was observed for coatings formed in an electrolyte containing 0.5 g/L of CdS, ZnO, and Dy₂O₃. The improved PA of Ta₂O₅/CdS, Ta₂O₅/ZnO and Ta₂O₅/Dy₂O₃ compared to Ta₂O₅ is related to the reduction of photogenerated electron/hole recombination. The mechanism of the photogenerated electron/hole transfer process is presented and discussed.

Layered metal sulfides are potential anode materials for lithium-ion batteries (LIBs) because their unique structure makes them suitable for Li⁺ de-intercalation. As a typical 2D layered material, MoS₂ is a potential anode material for LIBs due to the weak van der Waals forces between the layers, which facilitates the de-intercalation of Li⁺ and supports multiple Li⁺. However, when MoS₂ is used as anodes for LIBs material, rapid capacity decay hinders the application. Coupling two different materials to form a heterogeneous structure is an effective way to solve the above problems. In this work, one-pot hydrothermal method is proposed to construct MoS₂/SnS heterostructure composites. The electrochemical properties are significantly enhanced, which could be attributed to the presence of heterogeneous structures, leading to increase the electrode charge transfer rate and interfacial reaction kinetics. The results show that the discharge capacity of the MoS₂/SnS-1.5 electrode is about 1492.1 mAh/g at 500 mA/g. Furthermore, assembled MoS₂@SnS-1.5||LiCoO₂ full cell displays a high discharge capacity of 226.1 mAh/g after 50 cycles at 500 mA/g. This facile method provides the application value of layered metal sulfides as LIBs anode materials.

Periodically ordered δ-MnO₂ arrays of different periods have been fabricated by using polystyrene (PS) nanosphere lithography (NSL) combined with following hydrothermal growth. By choosing different precursors, δ-MnO₂ arrays with different alkali metals doping were obtained. It was observed that the K-doped δ-MnO₂ array of 500 nm period exhibited superior photocatalytic degradation performance of methylene blue (MB) under visible light irradiation relative to those of Na- or Mg-doped δ-MnO₂ arrays of 500 nm period, as well as K-doped δ-MnO₂ array of 800 nm period. The best performance of K-doped δ-MnO₂ array of 500 nm period can be firstly attributed to enhanced surface plasmon resonance (SPR) effect caused by alkali metal doping, where K-doped MnO₂ could provide more free electrons than those of Na- or Mg- doped MnO₂. Furthermore, for the nanomaterials with SPR effect the surface plasmon polaritons (SPP) can change the propagation path of incident light to vertical direction after scattering on them. Since the MnO₂ array of 500 nm period possessed the distance between neighbor unites smaller than the wavelength of irradiation light, and thus the scattered light interfered with each other after the incident light was scattered by the MnO₂ unites. Then the electric field (E-field) intensities generated by SPR effect near each MnO₂ unit were elevated due to the interference effect. Therefore, our finding may provide a peculiar way to improve SPR-mediated photocatalytic performance of non-metallic materials by combination of doping and arrays fabrication of particular periods.

The structural and magnetic properties of non-magnetic aluminium and magnetic neodymium substituted yttrium iron garnet samples (Y_3-xAl_xFe₅O₁₂ and Y_3-nNd_nFe₅O₁₂) were investigated. Powder samples were synthesized using auto combustion route. The Rietveld refinement analysis of the samples confirmed the presence of the garnet phase and showed presence of minimal impurity phases, specifically perovskite and hematite. Substitution on Y₃Fe₅O₁₂ with Al resulted in a linear decrease in saturation magnetization, while Nd substitution showed a non-linear change. In accordance with this the Internal Field Nuclear Magnetic Resonance (IFNMR) spectrum exhibited a downward shift in peak frequency when Al was substituted, and a significant reduction in intensity with Nd substitution in yttrium iron garnet samples. Aluminium ions take up either tetrahedral or octahedral positions in the lattice, apart from the dodecahedral site, because of their smaller ionic radii. This causes a decrease in the hyperfine field that originates from Fe³⁺ ions in tetrahedral and octahedral sites. On the other hand, neodymium ions occupy dodecahedral sites and are expected not to affect Fe ions. Concurrently, an observable peak shift was not observed in the IFNMR spectrum for Nd substitution. However, Nd substitution introduced strain in the lattice due to their larger ionic radii compared to yttrium, which they replace. This strain causes disorder in tetrahedral and octahedral sites and affects ⁵⁷Fe signal intensity. The magnetic properties observed from VSM analysis is also interpreted in view of observed changes in the ⁵⁷Fe IFNMR spectrum. X-ray Photoelectron spectroscopy (XPS) was employed mainly to explore spin orbit splitting of Fe 2p state in the samples.