Dielectric performance of pyrochlore-type Bi2MgNb2-xTaxO9 ceramics: The effects of tantalum doping

The solid solutions based on the pyrochlore-type system Bi₂MgNb_2-xTa_xO₉ were formed in the compositional range х = 0–2.0 (Bi_1·6Mg_0·8Nb_1.6-tTa_tO_7.2, t = 0–1.6). The Rietveld method was used to refine the structure for Bi₂MgNb_2-xTa_xO₉ (x = 0, 1.0, 2.0). The increasing tantalum content led to the slight decrease in the cubic unit cell parameters from 10.56934 (4) Å for x = 0 and 10.54607 (3) Å for x = 2 (sp.gr. Fd-3m:2). At the same time, tantalum additions suppressed grain growth in the pyrochlore ceramics during sintering and made it possible to obtain materials with an average grain size of 1–2 μm (Bi_1·6Mg_0·8Ta_1·6O_7.2). The increase in the Ta⁵⁺ concentration led to the decrease in the dielectric permeability from 104 (Bi_1·6Mg_0·8Nb_1·6O_7.2) to 20 (Bi_1·6Mg_0·8Ta_1·6O_7.2) at room temperature, while the dielectric loss tangent remained lower than 0.002, which is due to the small grain size and the high porosity of the samples. An increase in temperature has practically no effect on the values of the dielectric permittivity in the entire frequency range. The samples have weak through conductivity. The activation energies of electrical conductivity varied in the range of 0.84–1.00 eV, and the less tantalum, the lower the activation energy. The electrical properties of the samples at 200 Hz to 1 MHz are described by the simplest parallel scheme.     

Determination of optical and structural properties of lithium silicate ceramics with different ratios of Sm doped

In this study, the synthesis and luminescence characterization of Samarium (Sm³⁺) doped lithium metasilicate (Li₂SiO₃) phosphor ceramic were investigated. It was presented and discussed the results obtained on the luminescence and other optical studies such as X-ray diffraction (XRD), optical absorption and luminescence properties of Li₂SiO₃:Sm³⁺ phosphor ceramic. The Li₂SiO₃ compound was shown a characteristic phase in XRD. The doping in the lithium compound was not having a significant effect on the basic crystal structure of the material. The maximum photoluminescence (PL) emission for Sm³⁺ doped Li₂SiO₃ was observed at 554, 583, 641, 725 nm and bore resemblance to the visible region of the spectrum. The glow curves of all synthesized materials have a complex peak structure after being irradiated with a ⁹⁰Sr–⁹⁰Y beta source. In addition, the peak between 400 and 600 nm was seen in the radioluminescence (RL) spectrum because of a wide peak thought to be caused by silicate.     

Synthesis and characterization of G/TiO1.80 bulk composite thermoelectric material under high temperature and high pressure

The primary purpose of this work is to introduce the second phase of graphene (G) into non-stoichiometric TiO_1.80 successfully and optimize the thermoelectric properties of this composite material through high pressure and high temperature (HPHT) technology. The purpose of doping Ti powder under high pressure is to create a closed reducing atmosphere to change the ratio of titanium to oxygen in the titanium oxide base. The addition of graphene can considerably improve the electrical properties of the material and reduce its resistivity. An X-ray diffractometer, X-ray photoelectron spectrometer, scanning electron microscope, and transmission electron microscope were used to analyze and characterize the phase structure, chemical bond, micro morphology and crystal morphology of the samples. An abundance of grain boundaries and lattice dislocation defects can inhibit the lattice thermal conductivity. We also tested and analyzed the thermoelectric performance of the high-temperature and high-pressure synthetic samples through a variable temperature system. The variation of the absorption intensity of the ultraviolet UV spectrum with wavelength shows that high pressure can reduce the band gap, which is beneficial to the carrier transition and improves the conductivity of semiconductors. HPHT optimizes both the electrical and the thermal parameters of the sample. At a final sintering pressure of 5.0 GPa, the dimensionless figure of merit (zT) of the bulk composite material G/TiO_1.80 was found to be 0.23 at 700 °C.     

Deacetylated Cellulose Acetate/Polyurethane Composite Nanofiber Membranes with Highly Efficient Oil/Water Separation and Excellent Mechanical Properties

Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-M_CA:M_TPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-M_CA:M_TPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m⁻² h⁻¹, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-M_CA:M_TPU composite nanofiber membranes have great application prospects in oil/water separation.     

Scallops as a new source of food protein: high-intensity ultrasonication improved stability of oil-in-water emulsion stabilised by myofibrillar protein

In this study, the effect of high-intensity ultrasound (HIUS) (200 and 400 W for 0, 5, 10 and 15 min respectively) on conformational changes, physicochemical, rheological and emulsifying properties of scallop (Patinopecten yessoensis) myofibrillar protein (SMP) was investigated. HIUS-treated SMP had lower α-helix content and higher β-sheet content compared with the native SMP. HIUS treatment induced the unfolding of SMP and increased the surface hydrophobicity. The particle size of SMP decreased and the absolute zeta-potential increased after ultrasonication, which in turn increased the solubility of SMP. The conformational changes and the improvement of physicochemical properties of SMP increased the ability for SMP to lower the interfacial tension at the oil–water interface and increased the percentage of adsorbed protein. As a result, the emulsifying properties, rheological properties of SMP and storage stability of emulsions were also improved. In conclusion, HIUS treatment has future potential for improving the emulsifying properties of SMP.     

Anisotropic thermal expansion and ionic conductivity of a crystal-oriented,Mg2+-conducting NASICON-type solid electrolyte

Multivalent ion-conducting ceramics are required for the manufacture of high-safety, high-capacity rechargeable batteries. However, the low ionic conductivity of solid electrolytes and discrepancies in the thermal expansion between the battery components limit their widespread application. Furthermore, anisotropic thermal expansion in crystals during battery manufacturing and the charge-discharge cycles causes the formation of microcracks, which degrade the battery performance. The physical properties of ceramic materials with anisotropic crystal structures can be modified by varying the crystallographic orientation of their grains. In this study, a co-precipitation approach was used to synthesize an Mg²⁺-conducting (Mg_0.1Hf_0.9)_4/3.8Nb(PO₄)₃ solid electrolyte, and the grain orientation in the bulk sample was controlled using strong magnetic fields during the slip casting process. The results showed that inducing an orientation along the c-axis enhanced the apparent ionic conductivity of the bulk sample. It was also observed that (Mg_0.1Hf_0.9)_4/3.8Nb(PO₄)₃ crystal has a negative volumetric thermal expansion despite a positive linear thermal expansion along its c-axis. By adjusting the c-axis orientation of the grains, (Mg_0.1Hf_0.9)_4/3.8Nb(PO₄)₃ electrolytes with negative or positive linear thermal expansion coefficient have been produced. The findings of this study suggest that solid-electrolytes with negative, positive, or zero linear thermal expansion can be produced to create more compatible and higher-performance solid-state devices.     

Effect of low temperature crystallization on 58S bioactive glass sintering and compressive strength

Mesoporous glass 58S (60SiO₂, 36CaO, 4P₂O₅ mol.%) has excellent bioactivity, biocompatibility, and forms strong bonds with bone making it attractive for implants. Mesoporous bioactive glass 58S powder is typically consolidated through sintering in order to produce an implant with sufficient strength to withstand the in vivo loads. However, heating the glass often leads to crystallinity, which is undesirable because it can reduce bioactivity. Hence, there is a trade-off between minimising crystallinity and maximising glass strength. Even at relatively low temperatures, it has been suggested that segregation of calcium and phosphate from silica within the glass can lead to crystallization. In this work, we confirm the occurrence of low temperature segregation in bioactive glass 58S using electron microscopy with elemental mapping. We probe how segregation affects the material properties of post-sintered glasses via comparison to a glass where phase separation is prevented via addition citric acid to the parent sol.     

Mechanical Properties of Single-Layer Diamond Reinforced Poly(vinyl alcohol) Nanocomposites through Atomistic Simulation

Low-dimensional carbon nanostructures are ideal nanofillers to reinforce the mechanical performance of polymer nanocomposites due to their excellent mechanical properties. Through molecular dynamics simulations, the mechanical performance of poly(vinyl alchohol) (PVA) nanocomposites reinforced with a single-layer diamond – diamane is investigated. It is found the PVA/diamane exhibits similar interfacial strengths and pull-out characteristics with the PVA/bilayer-graphene counterpart. Specifically, when the nanofiller is fully embedded in the nanocomposite, it is unable to deform simultaneously with the PVA matrix due to the weak interfacial load transfer efficiency, thus the enhancement effect is not significant. In comparison, diamane can effectively promote the tensile properties of the nanocomposite when it has a laminated structure as it deforms simultaneously with the matrix. With this configuration, the interlayer sp³ bonds endows diamane with a much higher resistance under compression and shear tests, thus the nanocomposite can reach very high compressive and shear stress. Overall, enhancement on the mechanical interlocking at the interface as triggered by surface functionalization is only effective for the fully embedded nanofiller. This work provides a fundamental understanding of the mechanical properties of PVA nanocomposites reinforced by diamane, which can shed lights on the design and preparation of next generation high-performance nanocomposites.     

Grain orientation evolution and multi-scale interfaces enhanced thermoelectric properties of textured Sr0.9La0.1TiO3 based ceramics

Sr_0.9La_0.1TiO₃ based textured ceramics (SLTT-S3T) with a texture fraction of 0.81 are successfully fabricated by the reactive template grain growth method, in which Sr_0.9La_0.1TiO₃/20 wt%Ti was used as matrix and 10 wt% plate-like Sr₃Ti₂O₇ template seeds were used as templates. The phase transition, microstructure evolution, and the anisotropic thermoelectric properties of SLTT-S3T ceramics were investigated. The results show that the ceramics are mainly composed of Sr_0.9La_0.1TiO₃ and rutile TiO₂ phases. Grains grow with a preferred orientation along (h00). A maximum ZT of 0.26 at 1073 K was achieved in the direction perpendicular to the tape casting direction. The low lattice thermal conductivity of 1.9 W/(m K) at 1073 K was obtained decreased by 34%, 40%, and 38% compared with non-textured, SrTiO₃ and Sr_0.9La_0.1TiO₃ ceramics prepared by the same process, can be attributed to the enhanced phonon scattering by the complex multi-scale boundaries and interfaces. This work provides a strategy of microstructural design for thermoelectric oxides to decrease intrinsic lattice thermal conductivity and further regulate thermoelectric properties via texture engineering.     

Examining the Impact of Squaric Acid as a Crosslinking Agent on the Properties of Chitosan-Based Films

Hydrogels based on chitosan are very versatile materials which can be used for tissue engineering as well as in controlled drug delivery systems. One of the methods for obtaining a chitosan-based hydrogel is crosslinking by applying different components. The objective of the present study was to obtain a series of new crosslinked chitosan-based films by means of solvent casting method. Squaric acid—3,4-dihydroxy-3-cyclobutene-1,2-dione—was used as a safe crosslinking agent. The effect of the squaric acid on the structural, mechanical, thermal, and swelling properties of the formed films was determined. It was established that the addition of the squaric acid significantly improved Young’s modulus, tensile strength, and thermal stability of the obtained materials. Moreover, it should be stressed that the samples consisting of chitosan and squaric acid were characterized by a higher swelling than pure chitosan. The detailed characterization proved that squaric acid could be used as a new effective crosslinking agent.