We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact stru...We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.展开更多
The laser ablation technique was employed to prepare TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in the poly-(vinylpyrrolidone) solution using wavelength of 1 064 nm. The as-prepared prod...The laser ablation technique was employed to prepare TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in the poly-(vinylpyrrolidone) solution using wavelength of 1 064 nm. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the rutile TiO2 nanoparticles are synthesized at room temperature and the average size is about 35 nm with narrow size distribution. A possible formation mechanism was discussed and the UV-vis absorption and photoluminescence were measured. The optical study shows that rutile nanoparticle possesses direct optical transition with band gap of 3.15 eV.展开更多
The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method ...The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method within the generalised gradient approximation （GGA） for the exchange-correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on elec- tronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent, ionic and metallic bonds. Based on a Kramers Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant （~1 and z2, respectively） and the refractive index （n）; and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO2 for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.展开更多
In this work, structural and optical properties of the TiO2 films deposited on unheated substrates by dual cathode dc unbalanced magnetron sputtering at long substrate-target distance (ds-t) were studied. Titanium dio...In this work, structural and optical properties of the TiO2 films deposited on unheated substrates by dual cathode dc unbalanced magnetron sputtering at long substrate-target distance (ds-t) were studied. Titanium dioxide (TiO2) thin films were deposited on unheated Si (110) wafers, glass slides and carbon coated copper grids at different substrate to target (ds-t) distances. The structural properties of TiO2 thin films were characterized by X-ray diffraction (XRD) and transmission electron microcopy (TEM) with selected-area electron diffraction (SAED), surface morphology using atomic force microscopy (AFM) and optical transmission spectra using a spectrophotometer. XRD results show that TiO2 films deposited at various ds-t distances have only rutile crystal structure. The crystallinity and thickness of the films increased while the roughness decreased with decreasing ds-t distance. The refractive indices of the deposited films were found to be in the range of 2.51 - 2.82 and increased with decreasing ds-t distance.展开更多
Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and...Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and the magnetic moment mainly comes from p orbitals of O atoms around the Ti vacancy. However, the Ti vacancy under normal conditions is very difficult to form due to its high formation energy. Our calculations indicate that Li-doped TiO2 can reduce the formation energy while keeping the magnetism. The large magnetization energy indicates that Li-doped TiO2 is a promising room-temperature diluted magnetic semiconductor.展开更多
文摘We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.
基金Project(09R23) supported by the Scientific Research Starting Foundation of Nantong UniversityProjects(50671100, 10604055) supported by the National Natural Science Foundation of China
文摘The laser ablation technique was employed to prepare TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in the poly-(vinylpyrrolidone) solution using wavelength of 1 064 nm. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the rutile TiO2 nanoparticles are synthesized at room temperature and the average size is about 35 nm with narrow size distribution. A possible formation mechanism was discussed and the UV-vis absorption and photoluminescence were measured. The optical study shows that rutile nanoparticle possesses direct optical transition with band gap of 3.15 eV.
基金supported by the China Scholarship Council (CSC) and the National Natural Science Foundation of China (Grant Nos. 10676025 and 10574096)the Science-Technology Foundation for Young Scientist of Sichuan Province,China (Grant No. 09ZQ026-049)
文摘The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method within the generalised gradient approximation （GGA） for the exchange-correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on elec- tronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent, ionic and metallic bonds. Based on a Kramers Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant （~1 and z2, respectively） and the refractive index （n）; and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO2 for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.
文摘In this work, structural and optical properties of the TiO2 films deposited on unheated substrates by dual cathode dc unbalanced magnetron sputtering at long substrate-target distance (ds-t) were studied. Titanium dioxide (TiO2) thin films were deposited on unheated Si (110) wafers, glass slides and carbon coated copper grids at different substrate to target (ds-t) distances. The structural properties of TiO2 thin films were characterized by X-ray diffraction (XRD) and transmission electron microcopy (TEM) with selected-area electron diffraction (SAED), surface morphology using atomic force microscopy (AFM) and optical transmission spectra using a spectrophotometer. XRD results show that TiO2 films deposited at various ds-t distances have only rutile crystal structure. The crystallinity and thickness of the films increased while the roughness decreased with decreasing ds-t distance. The refractive indices of the deposited films were found to be in the range of 2.51 - 2.82 and increased with decreasing ds-t distance.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11005049 and 61006051)
文摘Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and the magnetic moment mainly comes from p orbitals of O atoms around the Ti vacancy. However, the Ti vacancy under normal conditions is very difficult to form due to its high formation energy. Our calculations indicate that Li-doped TiO2 can reduce the formation energy while keeping the magnetism. The large magnetization energy indicates that Li-doped TiO2 is a promising room-temperature diluted magnetic semiconductor.
