Novel SnO2@open microcell-liked graphene network as efficient detection for NO2

Abstract

The design of reduced graphene oxide (RGO) with novel porous structure has attracted tremendous attention owing to their larger specific surface area. Herein, three-dimensional open microcells, bowl-shaped RGO were fabricated through spray drying method which employed polystyrene spheres as a sacrificial template. The bowl-shaped, open microcell-liked pores observed in the RGO network had an average diameter of ≈1?μm. Subsequently, the catalytic SnO₂ nanoparticles were loaded on RGO network via a simple solvothermal method (SnO₂@RGO), and their gas sensing properties were investigated at room temperature (RT). In a comparison with pristine RGO network, the SnO₂@RGO composite exhibited almost 4 times higher response to 400?ppm NO₂ at RT and rapid recovery time. The extraordinary sensing performance can be attributed to the novel open microcell-liked porous microstructure with the SnO₂ catalyst nanoparticles.     

Effect of SnO2 on improvement on the microwave dielectric properties of Ba2Ti9O20

Effect of SnO₂ addition on the crystal structure/microstructure and the related microwave dielectric properties of the Ba₂Ti₉O₂₀ were systematically investigated. Incorporation of SnO₂ markedly stabilized the phase constituent and microstructure for the Ba₂Ti₉O₂₀ such that high quality materials can be obtained in a much wider processing window. The sintered density of the Ba₂Ti₉O₂₀ increased linearly, but the microwave dielectric constant (K) decreased monotonically, with the SnO₂ doping concentration. The quality factor (Qxf) of the materials increased firstly due to the addition of SnO₂, but decreased slightly with further increase in SnO₂ content. The best microwave dielectric properties obtained are K = 38.5 and Qxf = 31,500 GHz, which occurs for the 0.055 mol SnO₂-doped and 1350 °C/4 h sintered samples. These properties are markedly better than those for undoped materials (K = 38.8 and Qxf = 26,500 GHz).     

Control of magnetic anisotropy in Fe–Co–B soft magnetic underlayer for perpendicular magnetic recording media

Anisotropic residual stress induced in the Fe–Co–B/Ni–Fe layers causes high anisotropy field H _k in the films induced by magnetoelastic effect. The origin of residual stress in Fe–Co–B/Ni–Fe layers was investigated. The direction of magnetic anisotropy of Fe–Co–B/Ni–Fe layers was formed in the direction corresponding to the incident direction of sputtered particles reached substrate. The magnitude of the H _k depended strongly on the condition of argon gas pressure. An incident direction of sputtered particles, which has an important effect on the direction of H _k, seemed to be dispersed under high Ar gas pressure condition because of the increase of collision number between sputtered particles and Ar particles. However, a low gas pressure condition of 1 mTorr in which sputtered particles have a long mean free path led to restrain the dispersion of H _k direction. As a soft magnetic underlayer of high H _k, the noise level of the media with Fe–Co–B/Ni–Fe decreased about 4 dB compared to that with the layer of low H _k in low frequency.     

(Gd,Co, Ta)-Doped SnO<Subscript>2</Subscript> Varistor Ceramics

The effect on the microstructure and electrical properties of (Co, Ta)-doped SnO₂ varistors upon the addition of Gd₂O₃ was investigated. The threshold electric field of the SnO₂ based varistors increased significantly from 720 V/mm to 1455 V/mm, the relative dielectric constants of the SnO₂ based varistors decreased greatly from 833 to 330 as Gd₂O₃ concentration was increased up to 1.2 mol%. The significant decrease of the SnO₂ mean grain size, from 3.8 to 1.6 m with increasing Gd₂O₃ concentration over the range of 0 to 1.2 mol%, is the origin for increase in the threshold voltage and decrease of the dielectric constants. The mean grain size reduction is attributed to the segregation of Gd₂O₃ at grain boundaries hindering the SnO₂ grains from conglomerating into large particles. Varistors were found to have superhigh threshold voltage and comparatively large nonlinear coefficient . For 0.8 mol% Gd₂O₃-doped sample, threshold electrical field E and nonlinear coefficient were measured to be 1125 V/mm and 24.0, for 1.2 mol% Gd₂O₃-doped sample, E and were 1355 V/mm and 23.0. Superhigh threshold voltage and large nonlinear coefficient qualify the Gd-doped SnO₂ varistor as an excellent candidate in use for high voltage protection system.     

Sintering Behavior and Interfacial Analysis of Ni/Cu Electrode with BaTiO<Subscript>3</Subscript> Particulates

The sintering behavior of Ni electrode alloyed with Cu and the interfacial structure between Ni/Cu to BaTiO₃ (BT) have been investigated. The quantitative properties, which include thermal shrinkage, thermal expansion, wetting behaviors of Ni/Cu alloys on BT sheet, and composition distribution were measured by several thermal analysis techniques (TGA/DTA/TMA) and microstructural techniques (SEM/TEM/ HRTEM) with energy-dispersive spectroscopy (EDS). The shrinkage of the Ni/Cu/ BaTiO₃ composite tested in 5%H₂/N₂ atmosphere showed strong influence by the addition of Cu, and retarded slightly due to the addition of the BT particulates. The Cu alloyed with Ni improves the continuity of the electrode and does not trigger mutual reaction between Ni and BT.     

Effect of Cr additions on the electrical properties of Ni–BaTiO3 ultra-thin multilayer capacitors

Multilayer ceramic capacitors based on BaTiO₃ dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the continuity of ultra-thin Ni electrodes in Ni–BaTiO₃ multilayer capacitors could be achieved. Here, the effect of the Cr addition to the nickel electrode pastes is studied with regard to the electrical properties. Low-field electrical measurements demonstrate no major differences between Cr doped Ni and undoped Ni. However, high-field measurements show a significant decrease to the total capacitor resistance. Under a critical electrical bias the conductivity significantly increases due to a Fowler–Nordheim tunneling conduction though the interfacial Schottky barrier at the dielectric–electrode interface; the onset voltage of this conduction is much lower than with the undoped nickel. Based on these results, we evaluate criteria for the selection of an appropriate refractory metal in order to improve the Ni electrode continuity.     

Effect of Sn/Zn ratio on structure and photoluminescence properties of SnO2@ZnO composites

ABSTRACT

The SnO₂@ZnO composites, with Sn/Zn molar ratio (Sn/Zn–ratio) from 4:1 to 8:1, were successfully prepared via two–step hydrothermal method. The microstructure and morphology of the as–prepared Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. Furthermore, a reasonable growth mechanism of SnO₂@ZnO composites was proposed and the results indicated that the dispersity of SnO₂ nanowires on the ZnO nanorods surface was obviously influenced by the Sn/Zn–ratio. The photoluminescence (PL) properties of the Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. The results showed the opposite intensity change of ultraviolet (UV) and visible emission while the Sn/Zn–ratio increased. In addition, the possible emission mechanisms were also discussed that the UV emission is attributed to free–exciton recombination at the near–band edge and the potential difference between SnO₂ and ZnO result in the visible emission.     

Preparation of mono-disperse Ni powders via the reduction of hydrazine complexes: The effect of source materials and impurities

Mono-disperse and spherical Ni powders were prepared using a N₂H₄-based solution reduction route. The main focus was on manipulating the particle size by varying the source materials (Ni-chloride, Ni-sulfate and Ni-acetate) and impurity concentrations. The morphology and size of the Ni particle closely depended on the source materials. In addition, the particle size became significantly smaller with increasing Co concentration ranging from 0 to 350 ppm. The decrease in the Ni particle size was attributed to the promotion of nucleation by the rapid decomposition of the CoCl₂–N₂H₄ complex when adding a NaOH solution and the more active reduction of Co than that of Ni in the initial stages of the reaction.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

Assembling tin dioxide nanorods on carbon nanotubes by a chemical solution method

Nanocomposites have significant potential in development of advanced materials and nanotechnology applications. Here, multi-walled carbon nanotubes (MWCNTs) sheathed with tin dioxide (SnO₂) nanorods by a two-step chemical solution route are reported. Hydrolyzing of MWCNTs and SnCl₄·5H₂O at a near room temperature followed by alkali-assisted hydrothermal process resulted in perfect SnO₂ coating on MWCNTs. Based on the XRD and TEM results, we found the nanoscale SnO₂ rods covered densely on MWCNTs.     

NOx Sensing Properties of Varistor-Type Gas Sensors Consisting of Micro p-n Junctions

NO _x sensing properties of SnO₂-xCr₂O₃ as a varistor-type gas sensor have been investigated in the temperature range of 200–600°C. The breakdown voltage of SnO₂ shifted to a higher electric field upon exposure to NO₂ at 300–500°C, and the largest breakdown voltage shift, i.e. the highest NO₂ sensitivity was observed at 400°C. In contrast, the direction of the breakdown voltage shift in NO varied with temperature: the breakdown voltage shifted to a lower electric field at 300°C, but to a higher electric field at 500°C, and remained almost unchanged at 400°C. The NO₂ sensitivity of SnO₂ was superior to the NO sensitivity at every temperature, and then the SnO₂ exhibited good selectivity to NO₂ at 400°C. The breakdown voltage of Cr₂O₃ shifted in the reverse direction upon exposure to NO and NO₂, in comparison with those observed with SnO₂, owing to its p-type semiconductivity. Thus, Cr₂O₃ also exhibited certain sensitivity to both NO and NO₂ at 200°C, being more sensitive to NO₂, though the sensitivities decreased drastically at temperatures higher than 300°C. The addition of 5.0 wt% Cr₂O₃ to SnO₂ resulted in a significant improvement of NO and NO₂ sensitivities at 600°C, being accompanied by an increase in the breakdown voltage in air. Especially, the NO sensitivity was superior to the NO₂ sensitivity in the concentration range of 20–100 ppm, and then SnO₂ mixed with 5.0 wt% Cr₂O₃ was found to be the most suitable candidate for a NO sensor among the sensors tested. The increase in the breakdown voltage in air induced by the Cr₂O₃ addition was confirmed to arise from both the decrease in the particle size of SnO₂ and the formation of micro p-n junctions at grain boundaries. The decrease in the particle size was also responsible for the increased NO and NO₂ sensitivities, but the p-n junctions were suggested to play a more important role in promoting and stabilizing the chemisorption of NO at higher temperatures.     

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the stability of ultra-thin Ni electrodes in BaTiO₃-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for 5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point (Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO₃ interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase mass-transfer along the Ni-BaTiO₃ interfaces facilitating an acceleration of Ni electrodes discontinuities.     

Selective Gas Detection of SnO2-TiO2 Gas Sensors

The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H₂ gas sensing properties of SnO₂-TiO₂ composites were examined. SnO₂-TiO₂ composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H₂ gases were examined.With CuO-coating, SnO₂-TiO₂ composites showed the increased sensitivity to CO gas and a large difference in the sensing temperatures between CO and H₂ gases. As a result, CuO-coated SnO₂-TiO₂ composites showed the selectivity for CO gas between 100C and 190C and the selectivity for H₂ gas between 280C and 380C.     

Photocatalytic property of TiO2 loaded with SnO2 nanoparticles

2.5 nm-sized SnO₂ nanoparticles in rutile phase were loaded on the surface of 25 nm-sized TiO₂ (Degussa P-25) to form SnO₂/TiO₂ nano-composite structure. Up to 10 mol%, the loaded SnO₂ nanoparticles were well-dispersed on the surface of TiO₂ without mutual agglomeration. The SnO₂/TiO₂ with 1 mol% of SnO₂ demonstrated 1.5–1.7 times of photocatalytic activity compared to the pure TiO₂ in decomposing gaseous 2-propanol and in evolving CO₂. The role of SnO₂ nanoparticles on TiO₂ surface is considered to be retardation of recombination rate between electrons and holes by trapping the photo-excited electrons from the conduction band of TiO₂.     

Water–based synthesis of La0,5Sr0,5CoO3 (LSCO) electrodes for ferroelectric thin films

Abstract

La_0,5Sr_0,5CoO₃ (LSCO) thin films were prepared from water solutions of lanthanum nitrate La(NO₃)₃x6H₂O, strontium nitrate Sr(NO₃)₂ and cobalt nitrate Co(NO₃)₂x6H₂O with different amounts of polyvinylalcohol (PVA). Thin films were deposited on platinum coated and thermally oxidized silicon substrates. The influence of the amount of PVA on the thermal decomposition of LSCO precursors, the surface wetting and the microstructure of LSCO thin films were investigated. The effort was also focused on the optimization of the thermal treatment to obtain dense LSCO thin films.     

Preparation of SnO2 whiskers via the decomposition of tin oxalate

A new method for preparing SnO₂ whiskers by the decomposition of SnC₂O₄ is suggested. A Whisker-like morphology of a SnC₂O₄ precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl₂ aqueous solution (T > 50^∘C). In comparison, when the solution temperature was either lower than 50^∘C or when ethanol was used as the solvent, the SnC₂O₄ precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC₂O₄ precipitate remained even after its thermal decomposition into SnO₂ at 400^∘C indicating that SnC₂O₄ precipitation is a key step in preparing the whiskers. The formation mechanism of SnO₂ whiskers was explained by the supersaturation during the precipitation of SnC₂O₄.     

SnO2 nanocrystallines decorated g-C3N4 composites with enhanced visible-light photocatalytic activity

Abstract

A series of SnO₂ nanocrystallines decorated g-C₃N₄ architectures were synthesized using a facile solvothermal method. The structural, morphological, and optical properties of the as-prepared nanocomposites were characterized in detail, indicating that SnO₂ nanocrystallines with diameter ～ 4?nm were well-dispersed on the surface of g-C₃N_4. The photocatalytic activity of the composites was investigated by degrading rhodamine B (RhB) under visible light irradiation. The CNS2 heterostructure exhibits enhanced photocatalytic activity than bare SnO₂ and g-C₃N₄. Kinetic study revealed a promising degradation rate constant of 0.0593?min^?1 for the CNS2, which is 118 and 7 times higher than that of pure SnO₂ and g-C₃N₄, respectively. What’s more, the CNS2 still retained the photocatalytic activity after three cycle measurements. The enhanced photocatalytic performances of the nanocomposite may be due to its large surface area (116.2 m²/g), appropriate ratio of SnO₂/g-C₃N₄ and the compact structure of the junction between the SnO₂ nanocrystallines and the g-C₃N₄, which inhibits the recombination of photogenerated electrons and holes.     

Properties of anisotropic Ba‐Zn‐Cu system W‐type hexagonal ferrite magnets

Experiments were carried out to investigate the magnetic and physical properties of Ba‐Zn‐Cu W‐type hexagonal ferrites sintered without atmosphere control. Compositions were chosen according to the formula BaZn_2–xCu_xFe₁₆O₂₇, where x was varied 0 ˜ 0.5 and 1.0. The effect of BaO addition after semisintering treatment on magnetic properties of Ba‐Zn‐Cu compounds was examined. It was found that BaO addition for Ba‐Zn‐Cu compounds was very useful in stabilizing the W‐type hexagon. The optimum condition of making magnets and some properties of typical specimens are as follows: composition—BaZn_1.7Cu_0.3Fe₁₆O₂₇ with 4 wt% Ba added; semisintering conditions—1275 °C for 1.0 h in air; sintering conditions—1175°C for 0.5 h in air; magnetic properties and lattice constant are J_m = 0.405 T, J_r = 0.370 T, H_cJ = 88.15 kA/m, (BH)_max = 19.12 kJ/m³, T_c = 356 °C, H_A = 994.7 kA/m, K_A = 2.01 × 10⁵ J/m³, c = 32.928 × 10^–10 m, a = 5.927 × 10^–10 m, c/a = 5.556. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 36–42, 2001     

Degradation of Pt/PLZT/Pt capacitors caused by hydrogen in interlayer dielectrics

Abstract

A correlation between ferroelectric properties of the PLZT capacitors and amount of H₂ and H₂O gasses desorbed from interlayer dielectrics were investigated quantitatively. H₂ and H₂O gasses desorbed from interlayer dioxides were analyzed using thermal desorption spectroscopy. Polarization charges and its aging characteristics of memory array capacitors with area of 2 μm squares did not depend on amount of desorbed H₂ explicitly, but strongly on H₂O desorption. It is considered that silanol and hydroxyalkyl groups worked as hydrogen donor with catalytic activities of Pt top electrodes. As a result, hydrogen atoms should work as a major degradation agent for the imprint phenomena of memory array capacitors. Precise control of hydroxyl groups contained in the interlayer dielectrics and passivation films resulted in very small retention degradation caused by imprint phenomena, and realized high reliability and high density FRAM technologies.     

Effect of Precursor Concentration on Physical Properties of Cube-Like Zn2SnO4 Powders Synthesized by Co-Precipitation Method

Cube-like Zinc stannate (Zn₂SnO₄) spinel powders were synthesized by co-precipitation method using chloride starting precursors of zinc and tin. The influence concentration of precursors on relevant physical properties of Zn₂SnO₄ was investigated by increasing concentration of precursor material at 0.1 to 0.4 M (Zn:Sn at ratio 1:1). Structural properties of as-synthesized and Zn₂SnO₄ crystal were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray absorption spectroscopy (XAS). The results indicate that as-prepared material without calcination process is in cubic symmetry of zinc hydroxy stannate (ZnSn(OH)₆) affirmed by SEM and XRD results. Meanwhile, spinel phase of Zn₂SnO₄ with strong crystalline and eminent cubic structure can be achieved after calcination at 1000°C. Homogenous dispersion, high crystallinity and good cubic structure of Zn₂SnO₄ powders are occurred at higher concentration of precursors. Moreover, the oxidation state of these samples were investigated by the Zn K-edge and Sn L3-edge X-ray absorption near edge structure (XANES) using the synchrotron radiation light source. The analyses of XANES spectra revealed that the oxidation state of Zn was +2 and Sn valence was +4 in all Zn₂SnO₄ samples, which well corresponds to the theoretical values.