اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدCotunnite-structured titanium dioxide: the hardest known oxide
109
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Despite great technological importance and many investigations, a material with measured hardness comparable to that of diamond or cubic boron nitride has yet to be identified. Combined theoretical and experimental investigations led to the discovery of a new polymorph of titanium dioxide with titanium nine-coordinated to oxygen in the cotunnite (PbCl2) structure. Hardness measurements on the cotunnite-structured TiO2 synthesized at pressures above 60 GPa and temperatures above 1000 K reveal that this material is the hardest oxide yet discovered. Furthermore, it is one of the least compressible (with a measured bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa) polycrystalline materials studied thus far.
قيم البحث
اقرأ أيضاً
This study reports on the properties of nitrogen doped titanium dioxide $TiO_2$ thin films considering the application as transparent conducting oxide (TCO). Sets of thin films were prepared by sputtering a titanium target under oxygen atmosphere on
a quartz substrate at 400 or 500{deg}C. Films were then doped at the same temperature by 150 eV nitrogen ions. The films were prepared in Anatase phase which was maintained after doping. Up to 30at% nitrogen concentration was obtained at the surface, as determined by in situ x-ray photoelectron spectroscopy (XPS). Such high nitrogen concentration at the surface lead to nitrogen diffusion into the bulk which reached about 25 nm. Hall measurements indicate that average carrier density reached over $10^{19} cm^{-3}$ with mobility in the range of $0.1$ to $1 cm^2V^{-1}s^{-1}$. Resistivity about $3.10^{-1} Omega cm$ could be obtained with 85% light transmission at 550 nm. These results indicate that low energy implantation is an effective technique for $TiO_2$ doping that allows an accurate control of the doping process independently from the TiO2 preparation. Moreover, this doping route seems promising to attain high doping levels without significantly affecting the film structure. Such approach could be relevant for preparation of $N:TiO_2$ transparent conduction electrodes (TCE).
It is shown that in nanoporous titanium dioxide films, sensitivity to atmospheric hydrogen exposure and electroforming can coexist and are interdependent. The devices work as conventional hydrogen sensors below a threshold electric field while above
it, the well-known electroforming is observed. Offering hydrogen in this regime accelerates the electroforming process, and in addition to the usual reversible increase of the conductance in response to the hydrogen gas, an irreversible conductance decrease is superimposed. The behavior is interpreted in terms of a phenomenological model where current carrying, oxygen-deficient filaments with hydrogen-dependent conductivities form inside the titanium dioxide matrix.
The wealth of properties of titanium dioxide relies on its various polymorphs and on their mixtures coupled with a sensitivity to crystallographic orientations. It is therefore pivotal to set out methods that allow surface structural identification.
We demonstrate herein the ability of photoemission spectroscopy to provide Ti LMV (V = valence) Auger templates to quantitatively analyze TiO$_2$ polymorphs. The Ti LMV decay reflects Ti 4sp-O 2p hybridizations that are intrinsic properties of TiO$_2$ phases and orientations. Ti LMV templates collected on rutile (110), anatase (101), and (100) single crystals allow for the quantitative analysis of mixed nanosized powders, which bridges the gap between surfaces of reference and complex materials. As a test bed, the anatase/rutile P25 is studied both as received and during the anatase-to-rutile transformation upon annealing. The agreement with X-ray diffraction measurements proves the reliability of the Auger analysis and highlights its ability to detect surface orientations.
In this work, we have developed economic process to elaborate scalable titanium dioxide nanotube layers which show a tunable functionality. The titanium dioxide nanotube layers was prepared by electrochemical anodization of Ti foil in 0.4 wt% hydrofl
uoric acid solution. The nanotube layers structure and morphology were characterized using x-ray diffraction and scanning electron microscopy. The surface topography and wettability was studied according to the anodization time. The sample synthesized while the current density reached a local minimum displayed higher contact angle. Beyond this point, the contact angles decrease with the anodization time. Photo-degradation of acid orange 7 in aqueous solution was used as a probe to assess the photo-catalytic activity of titanium dioxide nanotube layers under UV irradiation. We obtained better photocatalitic activity for the sample elaborate at higher current density. Finally we use the Ciliated Protozoan T. pyriformis, an alternative cell model used for in vitro toxicity studies, to predict the toxicity of titanium dioxide nanotube layers in biological system. We did not observe any characteristic effect in the presence of the titanium dioxide nanotube layers on two physiological parameters related to this organism, non-specific esterases activity and population growth rate.
Based on first-principles calculations, we predict that the magnetic anisotropy energy (MAE) of Co-doped TiO$_2$ sensitively depends on carrier accumulation. This magnetoelectric phenomenon provides a promising route to directly manipulate the magnet
ization direction of diluted magnetic semiconductor by external electric-fields. We calculate the band structures and reveal the origin of carrier-dependent MAE in k-space. In fact, the carrier accumulation shifts the Fermi energy and regulates the competing contributions to MAE. The first-principles calculations provide a straightforward way to design spintronics materials with electrically controllable spin direction.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
