Defect-induced ferromagnetism in rutile TiO_2 : A first-principles study

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.     

A Three-dimensional Zinc 1,3,5-Benzenetricarboxylate with Rutile Topology Isolated in DMSO Solvothermal Reaction

A new zinc 1,3,5-benzenetricarboxylate Zn3(BTC)2(DMSO)4(BTC=1,3,5-benzenetricarboxylate) has been solvothermally synthesized in DMSO and structurally determined by X-ray single-crystal diffraction.It crystallizes in the monoclinic system,space group P21/c with a=10.0861(11),b=10.2527(11),c=16.4013(18),β=95.478(2)°,V=1688.3(3)3,Z=2,Zn3S4C26H30O16,Mr=922.85,Dc=1.815 g/cm3,F(000)=936,μ=2.434 mm-1,R=0.0319 and wR=0.0755.This compound consists of trimeric zinc clusters and BTC linkers.Alternate connection of these trimeric zinc clusters and BTC linkers results in a three-dimensional(3,6)-connected frame-work with rutile topology.     

Electronic structures and optical properties of TiO₂:Improved density-functional-theory investigation

TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha’s modified Becke-Johnson(TB-mBJ) exchange potential(plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation(LDA) and generalized gradient approximation(GGA),in contrast with substantially overestimated values from many-body perturbation(GW) calculations.As for optical dielectric functions(both real and imaginary parts),refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.     

Crystallography and crystallite morphology of rutile synthesized at low temperature

Rutile was prepared at low temperature with titanium trichloride in an acid- and oxygen-rich environment. Samples were characterized with X-ray powder diffraction, transmission electron microscopy, and thermogravimetry; rutile's crystalline structure was refined with the Rietveld method. Crystallites were needles with their largest dimension along c lattice parameter; they grew in bundles parallel to their length axis, and contained hydroxyls in their lattice and on their surface. When samples were annealed, dehydroxylation generated lattice defects that produced microstrains and created conditions for crystallite sintering at temperatures above 300°C. Titanium-oxygen interaction in rutile depended on the annealing temperature, which gave rise to changes in the symmetry of the representative rutile titanium-oxygen octahedron. The atomic bond length between the oxygen atoms shared by adjacent octahedra decreased with the temperature, contracting the lattice. All this was caused by the variation of the number of hydroxyls in the lattice.     

纳米化学复合镀Ni-P-TiO2(金红石型)及其耐蚀性能的研究

目前关于纳米化学复合镀Ni-P-TiO2,成为研究的热点,主要是研究TiO2具有光催化降解活性[1,2],以及通过对纳米TiO2进行掺杂能够增强它的光催化降解性能。本文以45#碳钢为基体,进行了纳米化学复合镀Ni-P-TiO2(金红石型),并对该镀层的耐腐蚀性能进行了研究。1实验部分1·1仪器及试剂LK98C(电化学综合测试系统,天津),磁力测厚仪(德国);试剂均为分析纯。纳米TiO2(金红石型)(上海正美亚公司);45#碳钢(圆柱形R5mm,矩形25·0×50·0×2·8mm)。1·2工艺流程45#铁基试样打磨→除油→水洗→除锈→水洗→活化→水洗→施镀。①除油配方工艺:20g/L…     

O deficiency in the rutile TiO2 (110) surface: Ab initio quantum chemical investigation of the electronic properties

The (110) surface of rutile TiO₂ (110) has been modeled using a density functional theory (DFT) plane‐wave pseudo‐potential method (CASTEP). In this study, 6 and 9 atomic‐layer slabs have been examined. The stoichiometric surface converges to a low‐spin solution in both cases with a density of states (DOS) similar to that for the bulk. O deficiencies are introduced by the removal of neutral O atoms thus leaving a neutral model with a surfeit of 2 e^? per vacancy. This results in the partial filling of the Ti t_2g conduction band orbitals and a compensatory shift in the Fermi level. The reduced surface converges to a high‐spin solution in all cases, with the excess spin located within the previously unoccupied Ti t_2g orbitals. Removal of the bridging surface O atoms results in an excess spin of 2 electrons per unit cell with approximately one‐half that for removal of in‐plane surface O atoms and subsurface O atoms. The removal of O atoms from the surface leads to an increase of the band gap, with the largest increase due to the removal of in‐plane 3‐fold coordinated surface O atoms, and the smallest one due to the removal of subsurface O atoms. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

95 ℃水溶液体系中TiCl4溶胶水解法制备纯金红石纳米粉体(英)

Titanium dioxide (TiO2) nanoparticles of rutile phase were synthesized by hydrolysis of TiCl₄ at 95 ℃ in aqueous solution. The samples as prepared and calcined at 500 ℃ were characterized by XRD, TG-DTA and TEM. The sample as prepared was of imperfect rutile structure, and its morphology was rod-like with a diameter of 10～20 nm, a length of 20～80 nm and an aspect ratio of 2～4. The structure of the sample calcined at 500 ℃ was a perfect rutile one, and its morphology was rod-like with a diameter of 15～25 nm, a length of 25～105 nm and an aspect ratio of 2～4. These results indicate that calcination temperature has a positive effect on the structure and the size of rutile nanocrystals, and has no effect on the aspect ratio of rutile nanocrystal. A model for the formation mechnism of rutile nanocrystal in aqueous solution under hydrolysis conditions has been proposed.     

Electron spin resonance investigation of the substitution of Fe3^＋ for Ti4^＋ ions in rutile TiO2 single crystal

A Fe doped rutile TiO 2 single crystal is grown in an O 2 atmosphere by the floating zone technique.Electron spin resonance (ESR) spectra clearly demonstrate that Fe 3+ ions are substituted for the Ti 4+ ions in the rutile TiO 2 matrix.Magnetization measurements reveal that the Fe:TiO 2 crystal shows paramagnetic behaviour in a temperature range from 5 K to 350 K.The Fe 3+ ions possess weak magnetic anisotropy with an easy axis along the c axis.The annealed Fe:TiO 2 crystal shows spin-glass-like behaviours due to the aggregation of the ferromagnetic clusters.     

Y掺杂纳米TiO2的合成及晶型转变过程

溶胶-凝胶;锐钛型;金红石型;Y掺杂纳米TiO2的合成及晶型转变过程