Tailoring structure and piezoelectric properties of CaBi2Nb2O9 ceramics by W6+-Doping

Calcium bismuth niobate (CaBi₂Nb₂O₉) is a typical bismuth-layer structured piezoelectrics (BLSPs) with a high Curie temperature (T_C) of ～943 °C, but it has low piezoelectric coefficient and high-temperature resistivity which severely limits signal acquisition in the high-temperature piezoelectric vibration sensors. Ion-doping modification is regarded as an effective way to enhance electrical properties. In this work, W⁶⁺ donor-doping at Nb⁵⁺ site in the CaBi₂Nb_2-xW_xO₉ (x = 0, 0.020, 0.025, 0.030, 0.035 and 0.040) piezoelectric ceramics with T_C of 931 ± 2 °C were fabricated by the conventional solid-state reaction method. The effects of W⁶⁺-doping on crystal structure of CaBi₂Nb_2-xW_xO₉ as well as microscopic morphology and electrical properties of ceramics were investigated systematically. The tetragonality, isotropy and electrical properties of the ceramics were enhanced with the introduction of W⁶⁺ dopant. It was found that x = 0.025 was the optimal W⁶⁺-doping ratio that yielded remnant polarization of 8.0 μC/cm², electrical resistivity of 3.0 × 10⁶ Ω cm at 600 °C, piezoelectric coefficient (d₃₃) of 14.4 pC/N, and good thermal depoling property. Our work has established a feasible approach to tune the structure of CaBi₂Nb₂O₉ to improve piezoelectric properties for potential applications in high-temperature piezoelectric vibration sensors.     

Self-cleaning functionalized FeNi/NiFe2O4/NiO/C nanofibers with enhanced microwave absorption performance

Microwave absorbing materials with enhanced microwave absorption performance and self-cleaning function are of great interest for military applications and human health caused by electromagnetic radiation pollution. Herein we report the synthesis of FeNi/NiFe₂O₄/NiO/C nanofibers (NFs) via electrospinning technique using nickel acetylacetonate (Ni(acac)₂), ferric acetylacetonate (Fe(acac)₃), and N, N-dimethylformamide (DMF)/polyacrylonitrile (PAN) solution as precursor. We also show the abilities of the materials to attenuate electromagnetic microwave and their ease of self-cleaning performance. X-ray diffraction patterns and HRTEM images reveal that the materials possess FeNi, NiFe₂O₄, NiO and graphite. HAADF-STEM images show that the magnetic nanoparticles distribute uniformly along the fibers. Contrast experiments had been conducted on different calcination temperatures to elucidate the impedance matching and loss mechanism. Based on the results of the experiment, excellent microwave absorption was exhibited by blending the NiFe₂O₄/NiO/CNFs and FeNi/NiFe₂O₄/NiO/CNFs into paraffin at 50 wt% and 5 wt%, respectively. Moreover, the contact angles (CA) of the as-prepared fiber films calcined at 650, 750 and 950 °C were 143°, 141° and 144°, respectively, indicating that fiber films exhibited excellent hydrophobicity and self-cleaning function. It suggested that the as-obtained NFs had an excellent application prospect in self-cleaning microwave absorbing materials.     

Synthesis and characterization of a cross-linkable nonlinear optical polymer functionalized with a thiophene- and tricyanovinyl-containing chromophore

This paper reports a novel nonlinear optical polymer BP-AVT-TCV functionalized with a thiophene- and tricyanovinyl-substituted chromophore. BP-AVT-TCV was synthesized by the post-tricyanovinylation of an epoxy-based precursor polymer BP-AVT, and had a high molar functionalization degree of chromophore (70 mol.%). It had an enhanced glass transition temperature (T_g = 164 °C) compared with BP-AVT (T_g = 114 °C), and a high decomposition temperature (T_d,5% = 295 °C). BP-AVT-TCV was further cross-linked to achieve the three-dimensional (3D) network of thermosetting polyurethane (PU). The poled PU films revealed an electro-optic (EO) coefficient (γ₃₃) value of 21 pm/V at a wavelength of 1315 nm. The structures of the polymers were confirmed by FT-IR, UV–Vis, and ¹H NMR spectra.     

W18O49 Nanowires as Ultraviolet Photodetector

Photodetectors in a configuration of field effect transistor were fabricated based on individual W₁₈O₄₉ nanowires. Evaluation of electrical transport behavior indicates that the W₁₈O₄₉ nanowires are n-type semiconductors. The photodetectors show high sensitivity, stability and reversibility to ultraviolet (UV) light. A high photoconductive gain of 10⁴ was obtained, and the photoconductivity is up to 60 nS upon exposure to 312 nm UV light with an intensity of 1.6 mW/cm². Absorption of oxygen on the surface of W₁₈O₄₉ nanowires has a significant influence on the dark conductivity, and the ambient gas can remarkably change the conductivity of W₁₈O₄₉ nanowire. The results imply that W₁₈O₄₉ nanowires will be promising candidates for fabricating UV photodetectors.     

Crystal structure,vibration characteristics and microwave dielectric properties of low loss MgMo1-xWxO4 solid solution ceramics

Solid-phase method was used to synthesize MgMo_1-xW_xO₄ (x = 0–0.15) ceramics. The influences of substitution Mo⁶⁺ with W⁶⁺ on crystal structure, vibration characteristics and microwave dielectric properties of MgMo_1-xW_xO₄ ceramics were comprehensively studied. X-Ray diffraction illustrated all samples exhibit single-phase monoclinic wolframite structure when x = 0–0.15, in which W⁶⁺ replaces Mo⁶⁺ sites formed solid solution. W⁶⁺ effectively improves sintering properties of the MgMoO₄, the average grain size and relative density were increased. Raman characterization reveals that suitable W⁶⁺ substitution amount leads to reduction of v₁ A_g peaks FWHM and the enhancement of specific v₃ A_g peak for Mo/WO₄ tetrahedron, which improves the ordered distribution of the crystal structure. The above combined effect results in the increased Q × f value, but has little influence of W⁶⁺ substitution on ε_r and τ_f for MgMoO₄. When x = 0.09, MgMo_0.91W_0.09O₄ ceramic sintered at 1050 °C has optimal microwave dielectric performance: ε_r = 7.21, Q×f = 90,829 GHz, τ_f = ?67 ppm/°C.     

Pulsed-laser deposited amorphous-like PZT thin-films: Microstructure and optical properties

Amorphous lead–zirconate–titanate (Pb_0.97Nd_0.02(Zr_0.55Ti_0.45)O₃, PNZT) thin-films were grown on single-crystal MgO(1 0 0) substrates at room temperature by pulsed laser deposition (PLD). Part of PNZT films was left as-deposited amorphous and others were post-annealed at temperatures from 100 to 400 °C. X-ray diffraction (XRD) and scanning probe microscopy (SPM) were used to characterize the microstructure. Optical properties were analyzed using spectrophotometry at UV–vis–NIR and prism-coupler method at 633 nm wavelengths. Initially, films were amorphous with a broad XRD peak around 2θ ≈ 29.7°. As the post-annealing temperature increased above 250 °C, the amorphous peak started to shift towards lower 2θ-angles and got narrower indicating of decreasing interatomic spacing and possible glass transformation. At the same time, the transmittance at all wavelengths increased remarkably, although no crystal structure was detected by XRD. Also, sharp optical TE₀ modes with full-width half-maximum (FWHM) values of Δβ ≈ 0.00067 could be coupled into these films.     

Effect of LMZBS glass on the microstructure and microwave dielectric properties of monocelsian ceramics

BaAl₂Si₂O₈–Li₂O–MgO–ZnO–B₂O₃–SiO₂ (BAS-LMZBS) glass ceramics were prepared through the solid-state route. The phase transformation, microstructure, bulk density and microwave dielectric properties of (1-x)BaAl₂Si₂O₈-xLMZBS(x = 0.1–0.4) the glass ceramics were examined. The effects of the LMZBS additive as a mineralizer on the hexagonal-to-monoclinic transformation were investigated by X-ray diffraction and scanning electron microscope. All of the hexagonal phases were converted into monoclinic phases when x = 0.1, and it was found that LMZBS glass affected the densification of the ceramic samples. Monocelsian was successfully prepared, and its sintering temperature was reduced from above 1400 °C–870 °C by adding LMZBS glass. Excellent microwave dielectric properties (ε_r = 7.31, Q × f = 48,926 GHz and τ_ƒ = −48 ppm/°C) were obtained at 870 °C. This sample shows great chemical compatibility with Ag electrodes and can be a promising candidate for practical applications of low-temperature, co-fired ceramics.     

Impact of TeO2–B2O3 manipulation on physical,structural, optical and radiation shielding properties of Ho/Yb codoped mixed glass former borotellurite glass

In this work, (75-x)B₂O₃-xTeO₂-11Bi₂O₃–10Li₂O-1Ho₂O₃-3Yb₂O₃ (x = 10–60 mol%) mixed glass former (MGF) glasses were prepared by using the melt-quenching method to investigate the effect of mixed glass former between B₂O₃ and TeO₂ on the structural, optical and radiation shielding properties of glass. The amorphous nature of the glass samples was confirmed through XRD measurement. Optical ultraviolet–visible light (UV–Vis) spectroscopy revealed that the direct and indirect optical band gap (E_opt) decreased as TeO₂ content increased except for the anomaly at x = 30 mol% due to the interchanging dominance of bridging oxygen (BO) and non-bridging oxygen (NBO) in the glass network. Both direct and indirect refractive indices, n posted an increment except for x = 30 mol% due to polarizability influence of BO and NBO. Urbach energy, E_u declined thus indicating lesser disorder and less defects on the glass structure. The radiation shielding properties of the glass samples were determined for 15 keV–15 MeV photon energy range by using Phy-X/PSD software. Atomic number-dependent parameters such as mass attenuation coefficient (MAC) and effective atomic number (Z_eff) demonstrated an enhanced performances caused by higher Z of Te over B. Meanwhile, density-dependent parameters such as linear attenuation coefficient (LAC), mean-free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) all exhibited an improvement over TeO₂ concentration due to higher density data obtained.     

Synthesis of Novel Double-Layer Nanostructures of SiC–WO x by a Two Step Thermal Evaporation Process

A novel double-layer nanostructure of silicon carbide and tungsten oxide is synthesized by a two-step thermal evaporation process using NiO as the catalyst. First, SiC nanowires are grown on Si substrate and then high density W₁₈O₄₉ nanorods are grown on these SiC nanowires to form a double-layer nanostructure. XRD and TEM analysis revealed that the synthesized nanostructures are well crystalline. The growth of W₁₈O₄₉ nanorods on SiC nanowires is explained on the basis of vapor–solid (VS) mechanism. The reasonably better turn-on field (5.4 V/μm) measured from the field emission measurements suggest that the synthesized nanostructures could be used as potential field emitters. Hyeyoung Kim and Karuppanan Senthil contributed equally to this article.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Solution combustion synthesis of iron-deficient Sc2-xFexO3 (x = 0.17-0.47) nanocrystals with bixbyite structure: The effect of spatial constraints

In this paper, nanopowders based on iron-deficient Sc_2-xFe_xO₃ (x = 0.17–0.47) nanocrystals with bixbyite structure and crystallite size of 3.7–38.9 nm were successfully synthesized via solution combustion. Variable glycine-to-nitrate (G/N) ratio was the main controlling factor. A wide range of experimental and computational methods were used to analyze the impact of spatial constraints on the resulting solid-state products. It was found that solution combustion mode greatly influenced on the temperature and gaseous products in the reaction zone. Volume (G/N = 0.4–0.8, T_max = 1179–1511 °C), self-propagating (G/N = 1.0–1.4, T_max = 614–957 °C) or smoldering (G/N = 0.2, T_max = 443 °C) combustion modes were acquired during the synthesis depending on G/N ratio. It was shown that the formation of impurity phases of am-Fe₂O₃ (T_max < 850 °C), c-Fe₃O₄ (900 °C < T_max < 1500 °C) or c-FeO (T_max > 1500 °C) was possible, depending on the combustion temperature. Besides, the combustion mode affected the porous and surfacial structure of resulting mesoporous nanopowders – specific surface area and total pore volume varied in ranges of 1.7–82.8 m²/g and 0.0088–0.1538 cm³/g, consequently. Chemical composition and unit cell parameters of Sc_2-xFe_xO₃ showed the positive deviation from Vegard's law. The average sizes of the interpore thickness (h) depending on G/N ratio were found from values of specific surface area and pycnometric density of nanopowders, which made it possible to establish the presence of spatial constraints for the crystals' growth of Sc_2-xFe_xO₃ at h values below 10 nm. Analysis of aspect (h/D) ratio allowed to determine synthetic parameters which led to mono- or polycrystalline structure of interpore space in resulting Sc_2-xFe_xO₃-based nanopowders. The results and patterns established in this paper allowed to synthesize a new type of foam-like functional materials based on rare-earth ferrites.     

Synthesis of a low-firing BaSi2O5 microwave dielectric ceramics with low dielectric constant

In this study, BaSi₂O₅ ceramics with an orthorhombic structure were synthesized by using a traditional solid-state method at a low temperature by doping with Li₂O–B₂O₃–CaO–CuO (LBCC) glass. The phase composition, mechanism of low-temperature sintering, microwave dielectric properties, and changes in the mesophase during the heating of low-temperature sintered BaSi₂O₅ ceramics were examined by performing an X-ray diffraction analysis. A compact matrix of BaSi₂O₅ can be wetted by the liquid phase of the formed LBCC glass. Therefore, LBCC glass with different doping percentages can effectively reduce the sintering temperature of BaSi₂O₅. The microwave dielectric properties of BaSi₂O₅ ceramics sintered at 900 °C at 4 wt% of LBCC glass were determined: ε_r = 7.32, Q × f = 19,002 GHz, and τ_f = ?35.8 ppm/°C. The chemical compatibility of the samples with Ag was studied at 4 wt% doping with LBCC glass, and the samples were fired for 4 h at 900 °C.     

Preparation and catalytic activity of K4Zr5O12 for the oxidation of soot from vehicle engine emissions

Pure phase K₄Zr₅O₁₂ is synthesized via solid state method in the present work. Various K/Zr ratios and temperatures are applied, and the synthesis process is investigated in detail by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Its catalytic activity for soot oxidation is studied by temperature programmed oxidation with different types of soot/catalyst contacts. It is revealed that K₄Zr₅O₁₂ is very active in the presence of 2–10% O₂ for both tight and loose contacts (T_p(tight) = 335 °C, T_p(ethanol) = 355 °C and T_p(shaking) = 370 °C). Thermal stability study shows that K₄Zr₅O₁₂ is highly stable up to at least 900 °C.     

Synthesis and investigation of a photosensitive,europium-containing polymer

A series of europium complexes containing polymeric reactivity groups have been successfully synthesized using a simple method. Among them, Eu(DBM)₂(Phen)(MA), which has the best fluorescence properties and solubility, was polymerized with glycidyl methacrylate (GMA) for use as a novel UV-written polymer material. The Poly (GMA-co-Eu(DBM)₂(Phen)(MA)) containing different proportions of europium were prepared, and their spectroscopic properties were investigated in detail. Polymer films with optimum proportions (a molar ratio between GMA and Eu(DBM)₂(Phen)(MA) of 15) exhibited good UV light lithograph sensitivities, strong visible fluorescence intensities, high glass transition temperatures (T_g: >170 °C), good thermal stabilities (T_d: up to 295 °C) and solvent resistances after crosslinking. Micro patterns with smooth top surfaces were fabricated from the resulting polymer by using direct UV exposure and chemical development.     

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2 films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO₂ thin films using dc dual magnetron (DM) sputtering in Ar + O₂ mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature T_surf measured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency f_r was investigated in detail. It was found that the increase of f_r from 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate a_D of sputtered TiO₂ films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO₂ films can be sputtered on unheated glass substrates at a_D = 80 nm/min, T_surf < 180 °C when high value of f_r = 350 kHz was used. Properties of a thin hydrophilic TiO₂ film deposited on a polycarbonate substrate are given.     

Epitaxial growth and characterization of dual-sided Y2O3 buffer layer for superconducting coated conductors

In this work, a dual-sided buffer template, which allows the deposition of YB₂Cu₃O_7-δ (YBCO) coated conductors on both sides, has been proposed and investigated. Theoretically, in contrast to traditional YBCO structure on one side, the performance of critical current in YBCO films has been improved by two times. In this buffer structure, the dual-sided Y₂O₃ films were grown on a flexible metal template by a home-made reel-to-reel dynamic direct current sputtering system and the film growth parameters were systematically investigated. The microstructure were characterized by in situ reflection high-energy electron diffraction monitoring in real time during the deposition stage. X-ray diffraction, and atomic force microscopy were used to detect the biaxial texture and surface morphology, respectively. What's more, by the application of stopping and range of ions in matter software, it helped us to understand the influence of deposition parameter to the growth rate of Y₂O₃ films. Finally, the biaxial texture of dual-sided Y₂O₃ film yielded out-of-plane texture of Δω = 4.2° and in-plane texture of ΔΦ = 5.2° for one side, as well as Δω = 5° and ΔΦ = 5.3° for the second side. Subsequently, the dual-sided YBCO superconducting films were coated on the above Y₂O₃ buffer layer by low-cost metal-organic chemical vapor deposition method with critical current of 30 A/cm and 60 A/cm for each side.     

Energy-saving glasses based on sodium tungsten bronze-like (Na5W14O44) functional units: Facile synthesis,NIR-shielding performance,and formation mechanism

Near-infrared (NIR)-shielding glasses for energy-saving window applications were prepared by forming sodium tungsten bronze-like (Na₅W₁₄O₄₄) functional units in the 29SiO₂–43B₂O₃–28NaF glass matrix. The glasses were synthesized by a facile melt-quenching process where 4–8 mol.% H₂WO₄ was added as the W source. The optimal glass was produced using 6 mol.% H₂WO₄, which had a low NIR transmission of 15.4% and a high visible light transmission of 59.8%. The possible mechanism for the formation of Na₅W₁₄O₄₄ in glasses were discussed based on XRD, Raman, XPS, XANES and EXAFS characterization of the glass samples, the glass samples after further crystallization, and the samples produced by staged heating of the starting materials. Crystalline or amorphous Na₅W₁₄O₄₄ formed during heating partially due to the protection by molten B₂O₃. Subsequently, amorphous Na₅W₁₄O₄₄ clusters are present in the glass acting as NIR-shielding functional units. This study sheds a light on further development of non-film-based and highly efficiency energy-saving windows.     

Antibacterial and photocatalytic active transparent TiO2 crystallized CaO–BaO–B2O3–Al2O3–TiO2–ZnO glass nanocomposites

Transparent TiO₂ crystallized 5CaO–10BaO–65B₂O₃–Al₂O₃–20TiO₂–10ZnO (CBBATZ) glass nanocomposites were fabricated using melt-quenching technique followed by specific heat treatments. As-quenched glass samples were provided three different heat treatments at 630°C for 3, 5, and 10 hours in order to obtain different amounts of TiO₂ nanocrystals in the glass. The presence of rutile phase of TiO₂ nanocrystals in glass was confirmed by X-ray diffraction. The glass nanocomposite heat treated for 10 hours showed a hydrophobic nature with contact angle of 90.90°. Contact angle decreased from 90.90 to 22.20°, when irradiated under ultraviolet (UV) radiation for 45 minutes. This photoinduced hydrophilicity showed a photocatalytic and self-cleaning properties of glass nanocomposite. During photocatalytic ink test, the maximum change in color of Resurin (Rz) ink and 60% degradation in absorbance of ink within 150 minutes under UV radiation were found for glass nanocomposite heat treated at 10 hours. Also, 78% degradation in absorbance of methylene blue dye (pollutant) within 180 minutes under UV irradiation was found for glass naocomposite heat-treated at 10 hours. Antibacterial performance of transparent glass nanocomposite against Escherichia coli was evaluated as well. More than 95% of the bacterial cells were degraded with glass nanocomposite heat-treated at 10 hours. CBBATZ glass nanocomposite found to impart the antibacterial effect through generation of reactive oxygen species (ROS) in aqueous medium. ROS species which was confirmed in the bacterial cell through intracellular ROS generation kit. During evaluation of mechanical properties using nanoindentation technique, the values of hardness and reduced modulus increased by ~26% and 10%, respectively, for glass nanocomposite heat-treated at 10 hours as compared to as-quenched glass.     

The first example of extended structure constructed from Knoth-type sandwich POMs and coordination fragments

A novel compound [P₂W₁₈M₃O₆₈][Cu(en)₂]₄·7H₂O·2OH^? (M = 0.5W + 0.5Cu) 1 which contains the first example of extended structure constructed from Knoth-type sandwich polyoxoanions and transition metal coordination complexes has been hydrothermally synthesized and characterized by elemental analysis, IR spectrum, UV–Vis spectrum and single-crystal X-ray diffraction analysis. Crystal data for 1: triclinic, space group, P-1, a = 13.2718(7) Å, b = 13.6432(8) Å, c = 25.7307(15) Å, α = 104.7340(10)°, β = 96.7630(10)°, γ = 90.0330(10)°, V = 4472.2(4) Å³, Z = 2. Structure solution and refinement based on 1090 parameters gave R1 (wR2) = 0.0409 (0.0993).     

Alkali metal tungsten bronze-doped energy-saving glasses for near-infrared shielding applications

Tungsten bronze has attracted global attention for its applications in near-infrared (NIR)-shielding windows. Here, alkali metal tungsten bronze (M_xWO₃, M = one or two types of Li, Na, and K)-doped glasses are prepared by a simple melt-quenching method. Their structure and properties were characterized by XRD, Raman spectroscopy, XPS and UV–Vis–NIR spectrophotometry. The effects of M on their structure and the NIR shielding performance are investigated. The LiF sample has the best NIR shielding performance, but its visible transmittance is sacrificed due to its low quality. The glasses containing mixed Li⁺ and K⁺ cooperate to form a high-quality Li⁺/K⁺-codoped tungsten bronze, while the glasses containing mixed Li⁺ and Na⁺ compete for limited tungsten resources to form Li⁺- and Na⁺-doped tungsten bronzes separately. The research here is helpful for understanding the role of different alkali metal ions in bulk energy-saving glass and is hugely significant for the guidance of the future applications of energy-saving glass without films.