The Mg2+/Ta5+ codoped rutile TiO2 ceramic with a nominal composition (Mg1/3Ta2/3)0.01Ti0.99O2 was synthesized using a conventional solid-state reaction method and sintered at 1400 °C for 2 h. The ...pure phase of the rutile TiO2 structure with a highly dense microstructure was obtained. A high dielectric permittivity (2.9 × 104 at 103 Hz) with a low loss tangent (<0.025) was achieved in the as-sintered ceramic. After removing the outer surface, the dielectric permittivity of the polished ceramic increased from 2.9 × 104 to 6.0 × 104, while the loss tangent also increased (~0.11). The dielectric permittivity and loss tangent could be recovered to the initial value of the as-sintered ceramic by annealing the polished ceramic in air. Notably, in the temperature range of −60–200 °C, the dielectric permittivity (103 Hz) of the annealed ceramic was slightly dependent (<±4.4%), while the loss tangent was very low (0.015–0.036). The giant dielectric properties were likely contributed by the insulating grain boundaries and insulative surface layer effects.
The microstructure and giant dielectric properties of Y3+ and Nb5+ co–doped TiO2 ceramics prepared via a chemical combustion method are investigated. A main rutile–TiO2 phase and dense ceramic ...microstructure are obtained in (Y0.5Nb0.5)xTi1-xO2 (x=0.025 and 0.05) ceramics. Nb dopant ions are homogeneously dispersed in the microstructure, while a second phase of Y2O3 particles is detected. The existence of Y3+, Nb5+, Ti4+ and Ti3+ as well as oxygen vacancies is confirmed by X–ray photoelectron spectroscopy and X–ray absorption near edge structure analysis. The sintered ceramics exhibit very high dielectric permittivity values of 104–105 in the frequency range of 40–106Hz. A low loss tangent value of ≈0.08 is obtained at 40Hz. (Y0.5Nb0.5)xTi1-xO2 ceramics can exhibit non–Ohmic behavior. Using impedance spectroscopy analysis, the giant dielectric properties of (Y0.5Nb0.5)xTi1-xO2 ceramics are confirmed to be primarily caused by interfacial polarization.
The microstructure, dielectric response, and nonlinear current-voltage properties of Sr2+-doped CaCu3Ti4O12/CaTiO3 (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method ...using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr2+ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr2+ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr2+, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr2+-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr2+-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces.
Pd-based catalysts supported on high-surface-area carbon are widely used in formic acid fuel cells. The composition, structure, and support can be modified to maximize the capabilities of Pd-based ...catalysts in terms of catalytic activity, durability, and cost. Various studies have investigated tuning the properties of Pd-based catalysts by alloying Pd with other metals. In this study, Cr, Ni, Cu, and Zn were incorporated into Pd-based catalysts. First, the effects of mole ratios were studied between Pd and the metals. The Pd
n
Ni ratios on a reduced graphene oxide support (Pd
n
Ni/rGO) were prepared using the one-pot method without the use of any surfactants. All obtained rGO-supported Pd
n
Ni catalysts (
n
= 1, 2, 4, with diameter of 5 nm) were used for the electrocatalytic oxidation of formic acid. The electro-oxidation measurements revealed that the Pd
n
Ni/rGO samples had superior electrocatalytic performance both in current densities and stabilities for formic acid oxidation (FAO) compared to Pd/rGO. Furthermore, Pd
4
Ni/rGO had greater electrocatalytic activity than the other Pd
n
Ni/rGO samples. In addition, with the same mole ratio of metals, Pd
4
Cr/rGO had higher efficiency toward FAO than the other series in the order: Pd
4
Cr/rGO > Pd
4
Ni/rGO > Pd
4
Cu/rGO > Pd
4
Zn/rGO.
In this work, the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene (PTFE) triboelectric nanogenerator ...(TENG). Enhancing surface area by a powerful O
2
and Ar bipolar pulse plasma etching without the use of CF
4
gas has been demonstrated for the first time. TENG with modified surface PTFE using a sequential two-step O
2
/Ar plasma has a superior power density of 9.9 Wm
−2
, which is almost thirty times higher than that of a pristine PTFE TENG. The synergistic combination of high surface area and charge trapping sites due to chemical bond defects achieved from the use of a sequential O
2
/Ar plasma gives rise to the intensified triboelectric charge density and the enhancement of power output of PTFE-based TENG. The effects of plasma species and plasma etching sequence on surface morphologies and surface chemical species were investigated by a field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The correlation of surface morphology, chemical structure, and TENG performance was elucidated. In addition, the applications of mechanical energy harvesting for lighting, charging capacitors, keyboard sensing and operating a portable calculator were demonstrated.
Two forms of zinc-aluminium layered double hydroxides (ZnAl-LDH) with borate association (iZA and cZA) were prepared by ion-exchange process and in-situ co-precipitation. The received materials were ...examined using several characterization techniques, e.g. x-ray diffraction (XRD), scanning- and transmission-electron microscopy (SEM and TEM). The XRD diffractograms suggested that only monoborate ions (possibly trigonal and tetrahedral forms) were involved in the intercalation and adsorption. Elemental analyses, i.e. inductive coupled plasma-optical emission and atomic absorption spectroscopies, were used to determine the starting zinc and boron compositions, and the contents after the dissolution experiment in water, soil, and plant growth study. The iZA and cZA samples were found to controlled-release Zn and B contents which can be used as micronutrient sources in agricultural application. The releases of the two nutrients are suggested to initiate from the anionic-exchange of BO33− and the transformation of Zn2+ from LDH basal plane. The plant experiments treated with these iZA and cZA exhibit improvements in plant growth, evidently attributed to the controlled and sustainable releases of boron and zinc for assisting macronutrient uptakes when used with the NPK fertilizer.
Boron and zinc are control-released as plant micronutrients via two pathways from synthetic layered double hydroxides. Display omitted
•Two forms of ZnAl-LDH with boron association are prepared from ion-exchange process and in-situ co-precipitation.•Trigonal and tetrahedral monoborate ions are intercalated in the LDH interlayer.•Controlled releases of Zn and B are obtained from different processes—Zn transformation to Zn2+ and B ion-exchange process.•Zn and B released from iZA and cZA improve the efficiency of NPK nutrient uptakes in plant.•cZA from co-precipitation method provides more boron that is suitable for the dicot-plant tomato.
We report the thermoelectric properties of thick bismuth-telluride (Bi2Te3) films deposited on polyimide substrates by DC magnetron sputtering and annealed at various temperatures (150–350 °C). The ...influence of annealing temperature on the microstructure and electronic structure of thick Bi2Te3 films is discussed. In this work, the annealed film at 250 °C has the best thermoelectric property due to highest electrical conductivity and Seebeck coefficient. The main effect of annealing temperature was really helpful to improve crystalline structure and enhance carrier mobility, whereas the carrier concentration was reduced due to the volatile of tellurium atom during annealing. Chemical states of bound and unbound atoms (Bi, Bi3+, Te, and Te2‐) on the surface play an important role in electrical properties. The exceed temperature caused the micro-crack formation and affect carrier transport by the scattering. The power factor of Bi2Te3 deposited by DC magnetron sputtering and annealed at 250 °C is comparable to the power factors of thick Bi2Te3 film deposited by various deposition techniques. The output power of single-leg, thick, thermoelectric Bi2Te3 film annealed at 250 °C as a function temperature generated a power of 0.98 μW at a temperature difference of 50 °C.
•Bi2Te3 film of more than 10 μm in thickness was deposited by magnetron sputtering•A maximum PF of 1.35 mW/K2m was obtained following annealing at 250 °C•Annealing treatment improved output power of Bi2Te3 thick film
High-performance ceramics with chemical formula (Ni1/3Ta2/3)xTi1−xO2 with excellent dielectric properties are demonstrated. The dopants of Ni2+ and Ta5+ in TiO2 caused the formation of oxygen ...vacancies and free electrons. The (Ni1/3Ta2/3)xTi1−xO2 exhibited low loss tangent of 0.046 and a high dielectric permittivity of 3.5–4.5 × 104 with a very weak dependence on temperature (−60 to 200 °C). Broadband dielectric spectroscopy shows at least four dominant sources in the dielectric relaxation response in the temperature range of − 253–210 °C. DFT calculations indicate the formation of defect clusters, which are the largest contributors to the dielectric response, and these are found to be dominant even at temperatures down to − 253 °C. Both grain boundary and surface layer mechanisms in the ceramics contribute to the dielectric response at the relatively high temperatures. The sample–electrode contact effect associated with oxygen vacancy diffusion is dominant at high temperatures above 150 °C.
Display omitted
•Co or Ni-N-MC is the first alternate design for CE electrocatalyst of DSCs.•An attempt to couple the CE electrocatalysts and the redox couples is considered.•Co or Ni-N-MC with high ...surface area shows excellent electrocatalytic activity.•DSC with Ni-N-MC CE shows a high efficiency of 8.42% in I−/I3− solution.•DSC with Ni-N-MC CE shows a high efficiency of 6.95% in T2/T− solution.
Nanocomposites of cobalt or nickel species and N-doped mesoporous carbon (Co-N-MC or Ni-N-MC) were prepared by in situ polymerized mesoporous silica-supported polyaniline (PANI) and then explored as the counter electrodes (CEs) in dye-sensitized solar cells (DSCs). It is shown that Co-N-MC and Ni-N-MC significantly improve the electrocatalytic activity toward the reduction of I3− compared to N-MC. These are attributed to combining high electrical conductivity of N-doped mesoporous carbon and high electrocatalytic activity of Co or Ni species into one material. The I−/I3−-based DSC using Ni-N-MC CE could reach a cell efficiency of 8.42%, which surpassed the efficiency of the DSC employing traditional platinized CE (8.22%). In addition, all N-doped mesoporous (N-MC (5.90%), Co-N-MC (6.80%), and Ni-N-MC (6.95%)) based DSCs showed higher performance than the cells with a platinized CE (5.25%) for the regeneration of organic redox couple, di-5-(1-methyltetrazole) disulfide/5-mercapto-1-methyltetrazole N–tetramethylammonium salt (T2/T−).
The effects of DC bias on the dielectric and electrical properties of co-doped (In
1/2
Nb
1/2
)
x
Ti
1−
x
O
2
(IN-T), where
x
= 0.05 and 0.1, and single-doped Ti
0.975
Nb
0.025
O
2
ceramics are ...investigated. The low-frequency dielectric permittivity (
′) and loss tangent of IN-T ceramics with
x
= 0.05 and 0.1 are greatly enhanced by applying a DC bias at 40 and 20 V, respectively, whereas the relatively high-frequency
′ remains unchanged. The induced low-frequency Maxwell-Wagner polarization completely vanishes by immediately applying no DC bias. After overload limited measurement, this polarization permanently emerges without DC bias, whereas the primary polarization remains unchanged. Using combined
Z
′′ and
M
′′ spectroscopic plots, it is found that the strongly induced-polarizations are contributed from the combination effects of the sample-electrode contact and resistive outer surface. Very high performance of the colossal permittivity in IN-T ceramics is attributed to the formation of a resistive outer-surface layer and insulating grain boundaries. These results not only provide important insights into the origins of the colossal dielectric response in the IN-T ceramic system, but are also important for deciding the doping conditions of TiO
2
-based materials for practical applications.
The effects of DC bias on the dielectric and electrical properties of co-doped (In
1/2
Nb
1/2
)
x
Ti
1−
x
O
2
(IN-T), where
x
= 0.05 and 0.1, and single-doped Ti
0.975
Nb
0.025
O
2
ceramics are investigated.
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