Effects of CuO additives and sol-gel technique on NiNb2O6 dielectric ceramics for LTCC application

The effects of CuO additives and sol–gel method synthesis on the sintering behavior, microstructure and the microwave dielectric properties of NiNb2O6 ceramics were investigated systematically. The NiNb2O6 ceramics were synthesized with traditional solid state method and sol–gel method, and the CuO additives were used in the solid state method for comparison. The sintering temperature of NiNb2O6 ceramics with the highest densification can be effectively reduced from about 1275 °C to 1050 and 1100 °C respectively by using CuO additions and sol–gel technique. To study their applicability in low temperature co-fired ceramic technology, dielectric properties have been characterized. The dielectric properties exhibited a significant dependence on the sintering condition, composition and crystal structure of the ceramics. In particular, the 2.5 wt% CuO-doped NiNb2O6 ceramics sintered at 1050 °C have excellent microwave dielectric properties: εr = 21.45, Q × f = 23,531 GHz, τf = −27.9 ppm/°C. While the NiNb2O6 ceramics prepared by sol–gel method obtain microwave dielectric properties as: εr = 19.16, Q × f = 11,149 GHz, τf = −27.3 ppm/°C after sintered at 1100 °C for 2 h

Correction: One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol–Gel Technique

Corrections to the author information and affiliations have been supplied

One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol–Gel Technique

American Chemical Society. Because of its electrically conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting material for applications in low-emission window coatings and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidation reactions. Here, we describe a novel nonaqueous sol-gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the nonhydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temperatures in the 160-260 °C range, compatible with coating processes on flexible plastic supports. The NP size distribution, shape, and dislocation density were studied by powder X-ray powder diffraction analyzed using the method of whole powder pattern modeling, as well as high-resolution transmission electron microscopy. The SnO2NPs were determined to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liquid-state13C and1H nuclear magnetic resonance (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of13C,1H, and119Sn solid-state NMR as well as Fourier transform infrared (FTIR) and Raman spectroscopy. The13C SSNMR, FTIR, and Raman data showed the presence of organic species derived from the 1-hexanol reactant remaining within the samples. The optical absorption, studied using UV-visible spectroscopy, indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mechanical strains present within the smallest NPs perhaps associated with the organic ligands decorating the NP surface. As the size increased, we observed a correlation with an increased density of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2NPs in the absence of chemical dopants

Titanium dioxide engineered for near-dispersionless high terahertz permittivity and ultra-low-loss

Realising engineering ceramics to serve as substrate materials in high-performance terahertz(THz) that are low-cost, have low dielectric loss and near-dispersionless broadband, high permittivity, is exceedingly demanding. Such substrates are deployed in, for example, integrated circuits for synthesizing and converting nonplanar and 3D structures into planar forms. The Rutile form of titanium dioxide (TiO2) has been widely accepted as commercially economical candidate substrate that meets demands for both low-loss and high permittivities at sub-THz bands. However, the relationship between its mechanisms of dielectric response to the microstructure have never been systematically investigated in order to engineer ultra-low dielectric-loss and high value, dispersionless permittivities. Here we show TiO2 THz dielectrics with high permittivity (ca. 102.30) and ultra-low loss (ca. 0.0042). These were prepared by insight gleaned from a broad use of materials characterisation methods to successfully engineer porosities, second phase, crystallography shear-planes and oxygen vacancies during sintering. The dielectric loss achieved here is not only with negligible dispersion over 0.2-0.8 THz, but also has the lowest value measured for known high-permittivity dielectrics. We expect the insight afforded by this study will underpin the development of subwavelength-scale, planar integrated circuits, compact high Q-resonators and broadband, slow-light devices in the THz band

Theoretical investigation of geometric configurations and vibrational spectra in citric acid complexes

The performance of advanced electronic ceramics is directly related to the synthesis route employed. Sol-gel methods are widely used for this purpose. However, the physicochemical intermediate steps are still not well understood. Better understanding and control of these processes can improve the final quality of samples. In this work, we studied theoretically the formation of metal complexes between citric acid and lithium or barium metal cations with different citric acid/metal proportions, using Density Functional Theory electronic structure calculations. Infrared and Raman scattering spectra were simulated for the more stable geometric configurations. Using this methodology, we identified some features of complexes formed in the synthesis process. Our results show that the complexes can be distinguished by changes in the bands assigned to C=O, COH-, and COO- group vibrations. An estimate of the most stable complexes is made based on total energy.Universidade Estadual PaulistaUniversidade Federal de São Carlos Departamento de FísicaUniversidade Estadual Paulista Faculdade de Ciências Departamento de FísicaUniversidade Estadual PaulistaUniversidade Estadual Paulista Faculdade de Ciências Departamento de Físic

A family history of type 2 diabetes increases risk factors associated with overfeeding

Aims/hypothesis: The purpose of the study was to test prospectively whether healthy individuals with a family history of type 2 diabetes are more susceptible to adverse metabolic effects during experimental overfeeding. Methods: We studied the effects of 3 and 28 days of overfeeding by 5,200 kJ/day in 41 sedentary individuals with and without a family history of type 2 diabetes (FH+ and FH− respectively). Measures included body weight, fat distribution (computed tomography) and insulin sensitivity (hyperinsulinaemic–euglycaemic clamp). Results: Body weight was increased compared with baseline at 3 and 28 days in both groups (p<0.001), FH+ individuals having gained significantly more weight than FH− individuals at 28 days (3.4±1.6 vs 2.2±1.4 kg, p<0.05). Fasting serum insulin and C-peptide were increased at 3 and 28 days compared with baseline in both groups, with greater increases in FH+ than in FH− for insulin at +3 and +28 days (p<0.01) and C-peptide at +28 days (p<0.05). Fasting glucose also increased at both time points, but without a significant group effect (p=0.1). Peripheral insulin sensitivity decreased in the whole cohort at +28 days (54.8±17.7 to 50.3±15.6 μmol min−1 [kg fat-free mass]−1, p=0.03), and insulin sensitivity by HOMA-IR decreased at both time points (p<0.001) and to a greater extent in FH+ than in FH− (p=0.008). Liver fat, subcutaneous and visceral fat increased similarly in the two groups (p<0.001). Conclusions: Overfeeding induced weight and fat gain, insulin resistance and hepatic fat deposition in healthy individuals. However, individuals with a family history of type 2 diabetes gained more weight and greater insulin resistance by HOMA-IR. The results of this study suggest that healthy individuals with a family history of type 2 diabetes are predisposed to adverse effects of overfeeding.D. Samocha-Bonet, L.V. Campbell, A. Viardot, J. Freund, C.S. Tam, J.R. Greenfield and L.K. Heilbron

Hexagonal ferrite fibres and nanofibres

Hexagonal ferrites, or hexaferrites, are hugely important materials commercially and technologically, with common applications as permanent magnets, magnetic recording and data storage media, components in electrical devices operating at wireless frequencies, and as GHz electromagnetic wave absorbers for EMC, RAM and stealth technologies. Hexaferrites are all ferrimagnetic materials, and their magnetic properties are intrinsically linked to their crystalline structures, all having a strong magnetocrystalline anisotropy; that is the induced magnetisation has a preferred orientation within the crystal structure. They can be divided into two main groups: those with an easy axis of magnetisation (known as uniaxial), the hard hexaferrites, and those with an easy plane (or cone) of magnetisation (known as ferroxplana or hexaplana), soft ferrites. The common hexaferrite members are: « M-type ferrites, such as BaFe12O19 and SrFe12O19« Z-type ferrites (Ba3Me2Fe24O41) « Y-type ferrites (Ba2Me2Fe12O22) « W-type ferrites (BaMe2Fe16O27) « X-type ferrites (Ba2Me2Fe28O46) « U-type ferrites (Ba4Me2Fe36O60) where Me = a small 2+ ion such as cobalt, nickel or zinc, and Ba can be fully substituted by Sr. Generally, the M ferrites are hard, the Y, Z and U ferrites are soft, and the W and X ferrites can very between these two extremes, but all have large magnetisation (M) values. There is currently increasing interest in composite materials containing hexaferrite fibres. It had been predicted that properties such as thermal and electrical conductivity, and magnetic, electrical and optical behaviour will be enhanced in material in fibrous form. This is because a continuous fine fibre can be considered as effectively one-dimensional, and it does not behave as a homogeneously distributed solid. Although the intrinsic magnetisation of the material is unaffected, the effective magnetisation of an aligned fibre sample should be greater when a field is applied parallel with fibre alignment compared to when applied perpendicularly to fibre alignment. This feature was first demonstrated by the author for aligned hexaferrite fibres in 2006. This chapter will deal with progress in the manufacture and properties of hexaferrite fibres, from the first syntheses of BaM, SrM, Co2Y, Co2Z, Co2W, Co2X and Co2U micron-scale fibres by the author 12-15 years ago, to recent developments in M ferrite hollow fibres and nanofibres, and hexaferrite-coated CNTs (carbon nanotubes).The relative properties of all reported hexaferrite fibres are compared and summarised at the end of this chapter. © (2016) Trans Tech Publications, Switzerland

Nanostructured titanium dioxide coatings prepared by Aerosol Assisted Chemical Vapour Deposition (AACVD)

Titanium dioxide is a compound of great interest, due to its functional properties; one of its most important uses is as a photocatalyst. TiO2 coatings can be deposited using different techniques. Aerosol Assisted Chemical Vapour Deposition (AACVD) is particularly interesting, as high temperature or pressure are not necessary to generate the gaseous precursors. Furthermore, by carefully choosing the deposition conditions (i.e. deposition temperature, solvent), it is possible to obtain deposits with different morphology and, consequently, different functional properties. In this paper we present the synthesis of titanium dioxide coatings with AACVD using complexes between titanium isopropoxide (TIPP) and acetyl acetone (acac) as precursors. Deposition experiments were performed using different ratios of TIPP to acac, to assess the effect on the composition of the coatings, their morphology and photocatalytic activity. Results showed that the use of acac led to nanostructured titanium dioxide (nanoparticles of about 10−25 nm diameter). Raman analysis showed the presence of both anatase and rutile phases. XPS analysis indicated the presence of residual carbonaceous species in the coatings; despite this, they displayed photocatalytic properties similar or superior to AACVD films without carbon. Photocatalytic tests, performed measuring the Formal Quantum Efficiency (FQE) and the Formal Quantum Yield (FQY) in the degradation of resazurin, showed that a acac:TIPP ratio equal to 1 led to the material with the highest performance, as the FQE value was about three times higher than that for the coating prepared with TIPP alone. Overall the complexes between TIPP and acac are promising precursors for the AACVD technique, leading to nanostructured coatings with enhanced performance

Pyrolysed cork-geopolymer composites: A novel and sustainable EMI shielding building material

In this investigation, and for the first time, pyrolysed sustainable cork was used to produce waste-based geopolymer-cork composites with enhanced electromagnetic interference (EMI) shielding properties. The influence of the pyrolysed cork amount and the geopolymer porosity on the EMI shielding ability of the composites was studied. The maximum total shielding effectiveness (SET) values achieved by these novel building materials (−13.8 to −15.9 dB) are equal to any other reported geopolymer microwave (MW) absorbers over the X-band, despite containing much lower carbon content. In addition, our composites were produced using an industrial waste (biomass fly ash) as raw material and recycled wine stoppers as a carbon source (2.5–3.75 wt%). This strategy is different from those implemented in the only other reported MW absorbing geopolymers, which used standard commercial chemical precursors, and the added carbon component is also a non-renewable commercial product, added in much greater quantities (10× more). Therefore, our approach not only decreases the consumption of virgin raw materials (e.g. kaolin), but also enhances the global sustainability of the construction sector