Narrow Results

In this review, the crystal structure and the synthesis of the sodium potassium niobate (K_0.5Na_0.5NbO₃) as a promising candidate for lead-free piezoelectrics are addressed. The sintering and the microstructure as prerequisites for obtaining ceramics with reliable and sufficiently high piezoelectric properties for selected applications are discussed.

Structural transformations during the synthesis of mayenite (Ca₁₂Al₁₄O₃₃) were investigated. The samples were prepared by a solid–state reaction and the transformations were researched by means of XRD, Rietveld analysis, SEM, and Raman spectroscopy. The three key phases (CaAl₂O₄, Ca₃Al₂O₆, Ca₅Al₆O₁₄) were identified and their role in the mayenite formation was assigned. The optimal low temperature pathway of the mayenite synthesis involving Ca₅Al₆O₁₄ intermediate was proposed.

Here we report a simple in situ template approach for the synthesis of uniformly-shaped straight carbon microtubes (SCMTs) under moderate conditions, in which zinc carbonate powder and glycol were used as starting materials. The morphology and microstructure of SCMTs were characterized by SEM, TEM, HRTEM, XRD and Raman spectrum. The length and diameter of SCMTs can be controlled by simply varying the concentration of zinc carbonate in glycol. Experimental results show that ZnO nanorods generated during the process act as an in situ template for SCMT formation. Owing to their large inner spacing, SCMTs may have potential applications in supporter materials for drugs, dyes, and catalysts, microreactors, and hydrogen or energy storage materials.

A Keggin-type vanadium-substituted tungstovanadozincic heteropoly acid H₇ZnW₁₁VO₄₀ ⋅ 8H₂O, with the transition metal as central atom, was firstly synthesized and characterized. Its proton conductivity was measured by the electrochemical impedance spectrum (EIS), and the result indicates that the H₇ZnW₁₁VO₄₀ ⋅ 8H₂O is a solid high-proton conductor with conductivity of 3.26 × 10^-3S ⋅ cm^-1 at 58°C, 50% relative humidity. Its activation energy is 29.50 kJ ⋅ mol^-1, which suggests that the mechanism of proton conduction is the Vehicle mechanism.

A ternary heteropoly acid (HPA) H₆SiW${}_{10}$V₂O${}_{40}\cdot$14H₂O was prepared and investigated in this paper. The structure feature and hydration of this HPA was characterized by IR, XRD, UV, and TG-DTA. This HPA exhibits a high proton conductivity, which is $7.4\times 10^{-3}$S$\cdot$cm${}^{-1}$ at 25${}^{\circ }$C and 70% relative humidity. It is a novel high proton conductor. The conductivity increases with higher temperature, and it exhibits Arrhenius behavior, with the activation energy value of 21.02kJ$\cdot$ mol${}^{-1}$ for proton conduction, indicating the proton conduction mechanism is dominated by vehicle mechanism.

Over the past a few years, high-quality graphene preparation has been evolved from low-yield micromechanical exfoliation in including a wide range of production methods, in particular by chemical vapor deposition (CVD). Here, we review the state-of-the-art on synthesis of graphene using CVD method and the strategies to control the graphene grain size, number of layers and morphology, mainly focusing on the graphene growth that uses Cu as substrate. We highlight the success of the past research in the field and provide a review of the methods that were used for such controlled synthesis.

Bi₂Mo_xW${}_{1-x}$O₆ microspheres are synthesized by simple one-step hydrothermal method and the morphological characterizations are performed by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), BET, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The gas sensing of Bi₂WO₆, Bi₂MoO₆ and Bi₂Mo_xW${}_{1-x}$O₆ is investigated. It can be concluded that the sensor of Bi₂Mo_xW${}_{1-x}$O₆ has the same good sensitivity as pure Bi₂MoO₆ and Bi₂WO₆ to alcohol. It is noteworthy that the operating temperature of Bi₂Mo${}_{0.67}$W${}_{0.33}$O₆ is 200^∘C which is lower than that of pure Bi₂WO₆ or Bi₂MoO₆ (240^∘C), so Bi₂Mo_xW${}_{1-x}$O₆ show its good property for alcohol gas sensing application.

Carbon nano-onion (CNO) (also known as onion-like carbon, OLC), exhibiting multiple enclosed fullerene shell structures, as one of the most promising nanoforms, has attracted worldwide attention during the past decades due to its exceptional chemical and physical properties such as non-toxicity, high chemical stability, large sufficient surface area with low density, and superior high electronic and thermal conductivities, visible photoluminescence, etc. Nowadays, functional CNOs have been applied in energy storage devices, supercapacitors, photovoltaics, light-emitting diodes and bio-imaging technology. Since the first observation of CNOs by transmission electron microscopy as a byproduct in the synthesis of carbon black in 1980, numerous experimental and theoretical studies including expressive practical applications of CNOs have been intensively developed in modern chemistry. With respect to synthetic techniques, the high-temperature annealing of nano diamond, detonation of high explosive molecules, arc discharge of graphite, chemical vapor deposition, laser ablation, thermal pyrolysis, hydrothermal carbonization, and microwave pyrolysis have been reported. It has been addressed that the synthesis approach plays a key role in determining the structure of CNOs and resultant properties. This paper reviewed the developments of CNOs through major synthesis methods utilized for a selected wide spectrum of applications, by covering both the past and current progress. The contents outlined in the current review will offer readers comprehensive insights into the design and development of CNO materials.

Co₂P nanocomposites were successfully synthesized via a facile hydrothermal method. The microstructure, morphology and elemental composition were examined by XRD, SEM, TEM and XPS. The effects of synthesis temperature and reaction time on the sensing properties of Co₂P nanocomposites were analyzed. The Co₂P sensor at 200${}^{\circ }$C and 3 h reaction condition exhibited optimum sensitivity toward 100 ppm ethanol. In comparison with other gases, ethanol possesses good selective characteristics at optimal operating temperature of 160${}^{\circ }$C, which greatly reduce energy consumption. The above results showed that Co₂P nanocomposites have the potential application as an effective sensor for ethanol detection.