Enhanced Pyroelectric Performance of Lead-Free Zn-Doped Na1/2Bi1/2TiO3-BaTiO3 Ceramics

Lead-free Na1/2Bi1/2TiO3-BaTiO3 (NBT-BT) has gained revived interest due to its exceptionally good high power properties in comparison to commercial lead-based piezoelectrics. Recently, Zn-modified NBT-BT-based materials as solid solution and composites have been reported to exhibit enhanced depolarization temperatures and a high mechanical quality factor. In this work, the pyroelectric properties of Zn-doped NBT-6mole%BT and NBT-9mole%BT ceramics are investigated. The doped compositions of NBT-6BT and NBT-9BT feature a relatively stable pyroelectric property in a wide temperature range of ~37 K (300–330 K) and 80 K (300–380 K), respectively. A threefold increase in detector figure of merit is noted for 0.01 mole Zn-doped NBT-6mole% BT at room temperature in comparison to undoped NBT-6mole%BT and this increase is higher than those of major lead-free materials. A broad range of the temperature-independent behavior for the figures of merit was noted (303–380 K) for Zn-doped NBT-6mole% BT, which is 30 K higher than the undoped material. The large pyroelectric figures of merit and good temperature stability renders Zn-doped NBT-BT an ideal candidate for pyroelectric detector and energy harvesting applications.

Perovskite Thin Film Materials Stabilized and Enhanced by Zinc(II) Doping

Recent work of ten different groups shows that the application of zinc-halides in lead perovskite materials results in a contraction of the d-space, stronger interaction with the organic cation, improved crystallization with larger crystal domains, a Goldschmidt factor closer to unity, smoother and denser thin films and an even distribution of Zn(II) (at the Pb(II) sites) throughout the material. These combined effects may lead to: (1) a substantially higher stability (even at ambient or high humidity conditions); (2) enhanced luminescent properties; (3) a higher power conversion efficiency (PCE) of the corresponding solar cell devices (up to PCE ~20%, with enhancement factors of 1.07 to 1.33 relative to undoped material).

Процессы переноса заряда в легировaнном натрием углеродном композите на основе фуллеренов и терморасширенного графита

The results of doping of a carbon composite material, in which fullerenes are located in a conductive matrix based on thermally exfoliated graphite, with a sodium dopant are presented. Charge transfer processes taking place in samples with different initial ratios of components are studied. It turns out that the electrical resistivity of the samples increases with the introduction of sodium and an increase in its content, since the mobility of the main charge carriers, which are holes as in the undoped material, decreases. The concentration of charge carriers in different types of samples varies in both directions and can increase by more than an order of magnitude. It is concluded that Na plays an ambiguous role. It can contribute not only to the generation of free electrons, but also to an additional increase in the concentration of various defects that can generate free holes and can affect, being effective traps and scattering centers, all types of charge carriers.

Effect of Alumina and Halloysite clay on Electrical tree growth in Silicone Rubber Nanocomposite

Nowadays Silicone Rubber (SiR) is recommended in high voltage cable accessories fabrication as it offers excellent electrical and mechanical properties. Electrical tree is one of the phenomenon which contributes to the main factor of SiR insulation breakdown. Recently, a new approach has been applied in order to enhance the insulation strength properties by introducing nano filler in undoped material. Thus, this paper presents the influence of nano-alumina and halloysite nanoclay on electrical tree growth in SiR at 0, 1 vol%, 2 vol% and 3 vol% concentration. The electrical tree growth was investigated at 8kVrms after tree inception voltage (TIV) within 30 minutes under room temperature. The results show reductions of electrical tree growth speed and accumulate damage (%) up to 2 vol% nano-alumina and up to 3 vol% halloysite nanoclay. Nevertheless the presence of 3 vol% nano-alumina in SiR leads to the faster electrical tree growth rate and the worst accumulate damage within 1 minute of electrical tree growth process.

PRODUÇÃO DE DOSÍMETROS TERMOLUMINESCENTES À BASE DE MgB4O7: Dy e MgB4O7:Tm

The thermoluminescent dosimetry (TL) is a well-established technique for the detection of ionizing radiation in hospitals, clinics, and industrial establishments where there is the need to quantify the radiation. For this practice is require the use phosphors which are sensitive to radiation. Some phosphors are already commonly used in this practice, for example, TLD-100 (LiF: Mg, Ti), CaSO4:Tm and CaSO4:Dy. A compound that was most recently introduced in dosimetry and has many advantageous features to detect neutrons, electrons and gamma is the magnesium tetraborate (MgB4O7), but the undoped material is not good for dosimetry, since signal does not show satisfactory thermoluminescence. The present work presents the analysis of the compound MgB4O7 when doped with rare earth elements, thulium (Tm) and dysprosium (Dy). The production of MgB4O7: Dy and MgB4O7: Tm occurred under acidic conditions. Following the process of crystal growth, several tests were made on phosphors produced to verify the quality of materials as TL dosimeter. Initially, was made the identification of the crystalline phases found in the material, using the technique of X-ray diffractometry, and then were evaluated and compared the TL emission curves of the crystals with two different types of dopants, to this, the samples were irradiated with different radiation sources: 137Cs (0,66 MeV), 60Co (1.25 MeV) and X-rays (0.41 MeV) and based on the results was evaluated the energy dependence of phosphors. Another characteristic analyzed, was the decay of TL signal for the material (fading). The results show that the material can be an excellent TL dosimeter when doped with rare earth elements Dy and Tm.

Synthesis and Characterization of Li4Ti5O12 Doped by Na and Al as Anodes Material for Li-Ion Batteries

Li4Ti5O12 pure and Li4Ti5O12 with Na and Al doped Li(3-x/3)AlxNaTi(5-2x/3)O12 (x=0, 0.025, 0.05, 0.075) as anodes for Li-ion batteries are synthesized at 850°C via solid state reaction using Li2CO3, TiO2-anatase, Al2O3 and Na2CO3 as precursor. The effect of substitution of Al and Na in Li4Ti5O12 on characterization of precursor and electrochemical performance is studied. It is found that Na doped in Li4Ti5O12 pure affected the formation of three phase i.e NaLiTi3O7, Li4Ti5O12, dan Li2TiO3. Meanwhile, Al doped contributed to the formation of NaLiTi3O7 phase significantly. The SEM images show that the particles have polyhedral shape with uniform size distribution. Na doped in the Li4Ti5O12 affected particle size become larger against Al doped particle size become smaller than undoped material, the best particle size measured by PSA is 30,89 . All characterization of material will determine the electrochemical performance of Li-ion battery.

The dopant type and amount governs the electrochemical performance of graphene platforms for the antioxidant activity quantification

Graphene doped with heteroatoms can show new or improved properties as compared to the original undoped material. Boron-doped graphene and nitrogen-doped graphene containing different amounts of dopants were compared for the detection of gallic acid.

Research on Low Temperature Performance of the F-doped LiFePO4/C Cathode Materials

F-doped LiFePO4/C cathode materials were synthesized by two-step solid-state reaction route. The F-doped LiFePO4/C increases the intrinsic conductivity, the diffusion of lithium ions, also improves the high-rate and low-temperature performances of LiFePO4. The SEM images reveal some small morphology changes of the two kinds of the materials, so the improved properties may not due to grain size changes but crystal structure changes. The F-doped material has a higher capability at low temperature. At -20°C, with the rate of 0.5C, the discharge capacity was 82mAhg-1, higher than that of undoped material(65mAhg-1) and the result is better than the previous study[17](65mAhg-1 at the rate of 0.3C), and the disparity would enlarge with the rate increased. The CV plots indicate that the doped material reveals less degree of polarization. F-doping sample improves the electrical conductivity of material, accelerating the process of Li+ deintercalation, therefore, improving the electrochemical performances at low temperature.

Multifunctional Thin Film Zinc Oxide Semiconductors: Application to Electronic Devices

In this paper we report some of the recent advances in transparent thin film oxide semiconductors, specifically zinc oxide (ZnO), produced by rf magnetron sputtering at room temperature with multifunctional properties. By controlling the deposition parameters it is possible to produce undoped material with electronic semiconductor properties or by doping it to get either n-type or p-type semiconductor behavior. In this work we refer our experience in producing n-type doping ZnO as transparent electrode to be used in optoelectronic applications such as solar cells and position sensitive detectors while the undoped ZnO can be used as UV photodetector or ozone gas sensor or even as active layer of fully transparent thin film transistors.

Properties of Ferromagnetic GaGdN

ABSTRACTSingle phase GaGdN and GaGdN:Si films were grown on sapphire substrates. The undoped films were highly resistive films but became conductive with the addition of Si. SQUID magnetometry indicated room temperature ferromagnetism in both types of materials. Structural defects had a strong influence on the magnetic ordering of the material, as seen in a drastic reduction of magnetic moment with degrading crystalline quality. Magnetization of the co-doped film increased with Si content, reaching levels higher than that of the undoped material. Gd-doped AlN films grown in a similar fashion also displayed Curie temperatures above room temperature.