Relationship between structural and dielectric properties of Znsubstituted Ba5CaTi2−xZnxNb8O30 tetragonal tungsten bronze

International audienceBa5CaTi2-xZnxNb8O30 ceramics with (x=0, 0.04, and 0.08) were synthesized by conventional solid-state reaction method at 1300°C for 6 hours. The effects of the Ti/Zn ratio on structural and dielectric properties were studied by changing the value of x. The pure phase formation of all prepared Ba5CaTi2-xZnxNb8O30 compositions was confirmed by X-ray diffraction. The refinement of the (XRD) data by the Rietveld method confirmed the tetragonal crystal structure with the space group P4bm at room temperature. Scanning electron microscopy (SEM) of Ba5CaTi2-xZnxNb8O30 ceramics shows good sinterability, low porosity and uniform distribution of grains of unequal size over the entire surface in all samples. The average grain size is in the range of 1.3 to 1.6 μm. The frequency-dependent dielectric properties were examined by complex impedance spectroscopy in the temperature range of 50°C to 420°C where a structural phase transition was observed for all samples

Very-low temperature synthesis of pure and crystalline lead-free Ba.85Ca.15Zr.1Ti.9O3 ceramic

The site-doping strategy of barium titanate (BaTiO3) is a promising way to develop new lead-free materials for energy with enhanced dielectric and piezoelectric properties. A novel strategy to elaborated pure and crystalline Ba.85Ca.15Zr.1Ti.9O3 (BCZT) ferroelectric powders at low temperature is proposed. It is based on sol-gel method followed by a hydrothermal reaction. The effects of preparation temperature on structure, crystallinity, purity, morphology and particles size distribution of BCZT powders were studied. It was clearly shown that pure and crystalline BCZT could be obtained over 80 °C. Furthermore, the BCZT particles exhibit a spherical shape whose mean size increases from 145 nm at 40 °C to 160 nm at 80 °C. The present study may provide a new strategy to design lead-free ferroelectric materials with enhanced structure and microstructure properties at very low temperature

Fast synthesis of crosslinked self-blowing poly(β-hydroxythioether) foams by decarboxylative-alkylation of thiols at room temperature

A novel strategy was developed to prepare a self-blowing poly(β-hydroxythioether) foam at room temperature by S-alkylation of 5-membered bis-cyclic carbonate using multifunctional thiol monomers. Two different thiol compounds, trimethylolpropane tris(3-mercaptopropionate) and pentaerythritol tetrakis(3-mercaptopropanoic acid) were used for the decarboxylative s-alkylation reaction. The thiol compounds simultaneously act as crosslinking agents and generate carbon dioxide during the decarboxylative s-alkylation reaction. This enables foam preparation without an external blowing agent. The use of tetrathiol monomer improves thermal stability, provides flexibility to the foams, and induces an increase in the glass transition temperature (Tg) due to a higher degree of cross-linking. The apparent density of the foams decreases with the increase of the tetrathiol ratio. This novel solvent-free approach paves the way to design sustainable foams with modular properties using accessible components and additives, as well as provides an alternative to non-isocyanate polyurethane foams.The CNRST of Morocco acknowledged for funding this work from Projet Prioritaire (PPR1/2015/73)Peer reviewe

Effect of Fabric Layering Sequence and Architecture on Mechanical Properties of Clay, Jute, and Glass Fibers Reinforced Polyester Laminated Hybrid Composites

Hybrid laminated composites are attracting a lot of attention these days. Indeed, mixing natural and synthetic fabrics in the same matrix completely exploits the components’ greatest properties. However, it has been proven that the use of particles such as clays increases the material performance. Hence, the aim of this study is to produce a new hybrid laminated composite system using the hand lay-up method and compression molding techniques. For this, a layering sequence of plain-woven jute fabrics and different architecture of E-Glass fibers (matt and plain-woven roving fabrics with different grammage) were selected to strengthen a polyester resin modified with a tiny amount of clays. The effects of hybridization, layering sequence, and weaving architecture were evaluated by means of mechanical tests. The dispersion and distribution of the charges in the polymeric matrix were also investigated by studying the material rheological properties. We conclude that the proposed hybridization may result in an optimal, superior, and cost-effective laminated composite that fits all the requirements of a given structure

Implementation and Characterization of a Laminate Hybrid Composite Based on Palm Tree and Glass Fibers

In this work, laminated polyester thermoset composites based on palm tree fibers extracted from palms leaflets and glass mats fibers were manufactured to develop hybrid compositions with good mechanical properties; the mixture of fibers was elaborated to not exceed 25 vol.%. Samples were prepared with a resin transfer molding (RTM) method and mechanically characterized using tensile and flexural, hardness, and impact tests, and ultrasonic waves as a non-destructive technique. The water sorption of these composite materials was carried out in addition to solar irradiation aging for approximately 300 days to predict the applicability and the long-term performance of the manufactured composites. Results have shown that the use of glass fibers significantly increased all properties; however, an optimum combination of the mixture could be interesting and could be developed with less glass sheet and more natural fibers, which is the goal of this study. On the other hand, exposure to natural sunlight deteriorated the mechanical resistance of the neat resin after only 60 days, while the composites kept high mechanical resistance for 365 days of exposure

Morphogenesis mechanisms in the hydrothermal growth of lead-free BCZT nanostructured multipods

Due to growing environmental concerns about the toxicity of lead-based piezoelectrics, the replacement of Pb-based materials with homologs with comparable piezoelectric properties but without lead is an emergent task. Since 2009, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) materials have aroused considerable attention as a replacement due to their excellent dielectric, ferroelectric and piezoelectric properties. Nanostructuring of BCZT can enhance these functionalities even more. Here, templated-growth of BCZT nanostructured multipods with hydrogen zirconate titanate nanowires (HZTO-NWs) was investigated under hydrothermal conditions. The effects of the precursor's concentrations and the hydrothermal reaction time on the morphological formation of BCZT nanostructures were investigated. Besides, composition, structure and phase analysis studies were carried out, and the growth mechanism of BCZT multipods was proposed. It was found that the precursor's concentrations and dwell time in hydrothermal reactions play a critical role in the formation of BCZT multipods, and the desirable BCZT phase was obtained in samples using low barium and calcium concentrations and at a short reaction time. This research has general validity and can be extended to design more complex perovskite oxides