Increase In Number Of Defects Research Articles

Zn-doped MnO2 ultrathin nanosheets with rich defects for high performance aqueous supercapacitors

A one-pot and energy-saving method was developed to manufacture defective manganese oxide materials. The insertion of zinc ions improves manganese oxide conductivity results in a significant increase in number of defects in the lattice to provide abundant active sites for energy storage. The synthesized zinc doped manganese oxide achieved a maximum capacity of 392 F g−1 in the three-electrode system, the corresponding supercapacitor reached an outstanding energy density of 55.28 Wh kg−1 at a power density of 555.6 W kg−1, while maintaining 95.2% of the initial capacity after 10,000 cycles. This research sheds new insights to the preparation of defective materials by a simple one-step method for energy storage applications.

Study of microstructure, electronic structure and thermal properties of Al2O3-doped tetragonal YSZ coatings

Al2O3-doped tetragonal yttria-stabilized zirconia (t-YSZ) coatings were prepared by plasma spraying under various spraying parameters. The analysis of variance reveals that only Al2O3 addition significantly affects thermal properties of coatings. The electronic structures and microstructures results show that the increase in number of defects and boundary density with the increasing addition of Al2O3 enhances phonon scattering resulting in a decrease in the thermal conductivity, which suggests that the Al2O3 addition can improve the insulation performance of the YSZ coating. The increase in boundary density with the increase in Al2O3 addition is due to recrystallization resulting from the decreasing melting point of Al2O3–YSZ composites, lattice distortion, and the presence of amorphous structure and monoclinic Al2O3 pinning at grain boundaries. The change in the coefficient of thermal expansion with Al2O3 addition is attributable to the variation in the bonding strength of the Al2O3-doped t-YSZ caused by the change in lattice constants.

Effect of tungsten doping on structural and optical properties of rutile TiO2 and band gap narrowing

Pure and W doped nanocrystalline rutile TiO2 samples were synthesized using high energy ball milling process. Rietveld refinement results of X-ray diffraction data confirmed that pure sample exhibited rutile TiO2 phase whereas doped samples contained both rutile TiO2 and a secondary Ti0.54W0.46O2 phase. Different models of Williamson–Hall method were employed to evaluate crystallite size and strain in the samples. The crystallite size was found to decrease from 50 to 47 nm with increase in the dopant concentration. The pure TiO2 exhibited tensile microstrain which became compressive and increased upon doping. A blue shift in A1g Raman mode with doping of W also indicated the increase in the compressive strain. The HR-TEM images also confirmed the presence of higher strain in doped samples compared to un-doped sample. The observed decrease in band gap from 3 to 2.83 eV with dopant concentration, as calculated from UV–vis spectroscopy data, may be attributed to the increased strain. The decrease in the intensity of photoluminescence emission indicated the increase in number of defects and oxygen vacancies with increasing dopant concentration. This is further, supported by the rise in Urbach energy, a signature of increased number of defects in doped samples. This study shows that the dopant induced strain plays significant role in band gap narrowing.

Processing and characterization of spark plasma sintered copper/carbon nanotube composites

A Copper (Cu) matrix composites reinforced with 0.2, 5 and 10vol% single walled carbon nanotubes (SWCNT) and 5 and 10vol% multi-wall carbon nanotubes (MWCNT) was processed by high energy attritor milling of pure copper powder with carbon nanotubes (CNT) and subsequently consolidated by spark plasma sintering (SPS). Microstructural characterization shows a network of CNT along the grain boundaries and the presence of porosities at grain boundaries as well as triple junctions. By covering the particle boundaries, the higher volume fraction of CNT makes the sintering difficult as compared to single phase copper or low volume fraction CNT composites. Raman spectroscopy indicates that there is an increase in number of defects in the nanotube after milling and sintering of the composite. Mechanical properties evaluation shows that SWCNT composites results in higher strength and deformability compared to MWCNT. The failure strain decreases with increase in volume percent of CNT due to clustering of CNTs.

EFFECT OF REPETITIVE PULSED LASER IRRADIATION ON PLASMA PLUME EMISSION INTENSITY AND SURFACE MORPHOLOGY OF 15 MeV ELECTRON-DEFECTED SILICON

In this work, laser induced plasma plume intensity and surface morphology of electron-defected silicon have been studied. For this purpose, the silicon (1 1 1) was irradiated with 15 MeV electrons at different doses (2000–10,000 cGy). The electron-defected silicon samples were analyzed by XRD and SEM, showing increase in number of defects (incubation or absorption centers) by increasing electron dose. Afterward, repetitive Nd:YAG laser pulses were applied to electron-defected silicon. The plasma plume due to each laser pulse was photographed by computer controlled image capture system. From the images, the integrated intensity of plasma plume was calculated by image processing software and plotted as a function of number of laser pulses. The plasma plume intensity was found to increase linearly with increasing pulse number for all silicon samples. The integrated intensity of plasma plume also increases for those silicon samples which were irradiated at higher electron doses. The surface morphology of laser-ablated electron-defected samples was examined through SEM showing different phenomena, like thermal, electronic and hydrodynamic sputtering processes along with the formation of cone, craters, re-deposition of material, heat affected zone (HAZ) and debris formation.

Ab initiomodels of amorphousSi1−xGex:H

We study the structural, dynamical, and electronic properties of amorphous ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}:\mathrm{H}$ alloys using first-principles local basis molecular dynamics techniques. The network topology and defects in the amorphous network have been analyzed. Structural changes, particularly an increase in number of defects and strained bond angles, have been found as the Ge content increases from $x=0.1$ to 0.5. The electronic density of states exhibits a decreasing band gap and additional midgap and band-tail defect states as Ge concentration increases. We report the network structures which are responsible for midgap and band-tail states. The band tails show an exponential (Urbach) behavior. The mobility gap is coarsely estimated as a function of Ge concentration.