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1.
We present here a study of the electronic and optical properties of rutile (TiO2). An investigation into the energy, pressure and temperature dependence of neff and ε∞ eff is presented. Using the calculated values of neff and ε∞ effs, we evaluate the Penn gap. The Penn gap thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from band structure. In addition, we also show that essentially the Varshni formula explains the temperature dependence of the energy gap for rutile fairly well. 相似文献
2.
D. Zwingel 《Solid State Communications》1978,26(11):775-777
The EPR spectrum of a trapped hole center in Ga-doped TiO2 is reported. The electronic structure of the center is discussed in view of the electron configuration of the Ga3+ ion. 相似文献
3.
Paraelectric resonance experiments on slightly reduced, aluminium doped rutile single crystals are reported. In the region 32–37 GHz at reduced He-temperatures a single resonance line is observed which is ascribed to an orientable electric dipole constituted of a multiply localized electron and an interstitial Ti3+ ion. 相似文献
4.
Haowei Peng 《Physics letters. A》2008,372(9):1527-1530
Native point defects in the rutile TiO2 are studied via first-principles pseudopotential calculations. Except for the two antisite defects, all the native point defects have low formation energies. Under the Ti-rich growth condition, high concentrations of titanium interstitials and oxygen vacancies would form spontaneously in p-type samples; whereas high concentrations of titanium vacancies would form spontaneously in n-type samples regardless of the oxygen partial pressure. 相似文献
5.
Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO2, GeO2 and SnO2 are described. At room temperature, the TiO2 II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO2-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO2 phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO2 are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO2, where p-electron bonding is involved, is much less Enharmonic. 相似文献
6.
L.E. Firment 《Surface science》1982,116(2):205-216
Temperature dependent faceting of rutile TiO2 surfaces cut to the (001) plane has been reported [Tait and Kasowski, Phys. Rev. B20 (1979) 5178]. By comparing LEED data to beam positions calculated for various sets of facet planes, the facet planes have been identified. The first ordered structure observed on annealing ion bombarded surfaces is composed of {011} facets with the facet planes in a (2 × 1) reconstruction. The high temperature structure produced on annealing above 1300K is best described as {114} facets; however, there are deviations of the observed LEED pattern from that calculated for {114} facets, possibly because of the presence of related planes. LEED data have now been obtained on the behavior of (110), (100), (011), (114), and (001) surfaces in UHV. The observed stability of TiO2 surfaces can be related to the Ti ion coordination numbers in the surface plane as derived from stoichiometric terminations of the rutile lattice. 相似文献
7.
H. Sawatari E. Iguchi R.J.D. Tilley 《Journal of Physics and Chemistry of Solids》1982,43(12):1147-1155
The formation energies for the point defect species Ti4+ interstitials, Tii4+, and oxygen vacancies with an effective charge of + 2e, Vo2+, have been calculated using the polarisable point ion shell model. The formation energy of Tii4+ was found to be a 10.8 eV for occupation of the (0, , ) site. The energy of Tii4+ at other sites is somewhat higher than this figure, and allowed the migration energy of Tii4+ parallel to the c axis to be estimated as 2.9 eV. The formation energy of Vo2+ was found to be 10.1eV. The variation of these formation energies with dielectric constant was also calculated. It was found that the energy of formation of Tii4+ varied considerably with dielectric constant, while the formation energy of Vo2+ was almost independent of dielectric constant. The relevance of these results to the presence of crystallographic shear planes in reduced rutile is considered. 相似文献
8.
This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO 2,HfO 2 and rutile TiO 2 (001) by using classical molecular dynamics.It is found that these three surfaces relax instead of reconstruction at 0 K,and have little possibility to reconstruct below 40 K.Above 40 K,surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain.Several reconstruction patterns with approximate surface energies are found,and electrostatic potentials on them are also provided in comparison with possible microscopic results. 相似文献
9.
We report the first Raman investigation of the rutile material RuO2. The four allowed first-order Raman-active phonon modes have been observed and classified. Comparison is made with other rutile materials. 相似文献
10.
Titanium dioxide (TiO2) rutile single crystal was irradiated by infrared femtosecond (fs) laser pulses with repetition rate of 250 kHz and phase transformation of rutile TiO2 was observed. Micro-Raman spectra show that the intensity of Eg Raman vibrating mode of rutile phase increases and that of A1g Raman vibrating mode decreases apparently within the ablation crater after fs laser irradiation. With increasing of irradiation time, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO2 single crystal is partly transformed into anatase phase. The anatase phase content transformed from rutile phase increased to a constant with increasing of fs pulse laser irradiation time. The study indicates the more stable rutile phase is transformed into anatase phase by the high pressure produced by fs pulse laser irradiation. 相似文献
11.
利用基于密度泛函理论的第一性原理研究了I掺杂金红石TiO2(110)表面的形成能和电子结构,分析了不同掺杂位置的结构对TiO2光催化性能的影响. 计算表明,氧化环境下I最容易替代掺杂表面五配位的Ti,而还原环境下最容易替代掺杂表面的桥位氧. I替位Ti或I替位O都能降低禁带宽度,可能使TiO2吸收带出现红移现象或产生在可见光区的吸收,其中I替位桥位氧的禁带宽度最小. 吸收光谱表明,I掺杂不仅能提高TiO2可见光响应,同时可增加紫外光的吸收能量,提高其可见光及紫外光下的光催化性能.
关键词:
第一性原理
I掺杂
2(110)')" href="#">金红石相TiO2(110)
光催化 相似文献
12.
S. Güler B. Rameev R.I. Khaibullin B. Akta? 《Journal of magnetism and magnetic materials》2010,322(8):L13
Single crystals of Mn-implanted TiO2 rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. We have observed an EPR signal on Mn4+ ions (S=) in the manganese-implanted single crystal TiO2 plates. Besides, weaker EPR signals due to Fe3+(S=, L=0) and Cr3+(S=) ions have also been observed. Characteristic six-line splitting of the manganese EPR lines due to hyper-fine interaction with 55Mn nuclei (spin I=) has also been observed. Analysis of the EPR spectra shows that the manganese, iron and chromium ions substitute for Ti4+ ions in the TiO2 rutile host. Two structurally equivalent groups of the centers have been observed in the EPR spectra in correspondence with two octahedral positions of the Ti ions in the rutile structure. Spin Hamiltonian parameters for the crystal field of orthorhombic symmetry on the Mn4+, Fe3+ and Cr3+ centers have been obtained as result of computer modelling. 相似文献
13.
The analysis of the infrared reflectivity spectrum of partially reduced rutile TiO1.96 reveals a plasmon-LO phonon coupling. Pure-phonon and plasmon frequencies and life times are determined by fit with an appropriate model using the factorized form of the dielectric function for the phonon modes added to a plasmon contribution also derived from the factorized form. Results are compared with data obtained in the insulating stoichiometric rutile. 相似文献
14.
Roman Sikora 《Journal of Physics and Chemistry of Solids》2005,66(6):1069-1073
The local-density approximation is used to find the phonon dispersion relations, total and partial phonon density of states for TiO2 crystal of rutile structure. For that the Hellmann-Feynman forces were computed and direct method applied. Some thermodynamic quantities are also presented. Calculated results are analyzed and compared with the experimental neutron scattering and optic data. Good agreement has been achieved. A giant LO/TO splitting is observed for A2u and Eu modes. 相似文献
15.
C. Vettier 《Journal of Physics and Chemistry of Solids》1975,36(5):401-405
A full three-dimensional structure determination of FeCl2 has been performed at hydrostatic pressures up to 6.4 kbar at room temperature. These studies demonstrate the feasibility of four-circle neutron diffraction studies under pressure, and show that above 5.8 kbar FeCl2 has a structure isomorphous to FeBr2. The pressure dependence of chlorine position parameter and lattice parameters has been studied over the entire pressure range. 相似文献
16.
The electronic, structural properties and optical properties of the rutile TiO2 have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. Our results including lattice parameter, bulk modulus, density of states, the reflectivity spectra, the refractive index and band gap are compared with the experimental data. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε1(0). 相似文献
17.
A combined study of IR absorption, photoconductivity, photoluminescence and Raman measurements in ZnO samples supports the theoretical suggestions of a shallow bond-centered hydrogen donor and a shallow hydrogen donor within the oxygen vacancy. In rutile TiO2 we also identify a shallow hydrogen donor in contrast to recent theoretical predictions. A possible solution to this obvious discrepancy is proposed. 相似文献
18.
Wen-Jin Yin Bo Wen Chuanyao Zhou Annabella Selloni Li-Min Liu 《Surface Science Reports》2018,73(2):58-82
As a prototypical photocatalyst, TiO2 is a material of scientific and technological interest. In photocatalysis and other applications, TiO2 is often reduced, behaving as an n-type semiconductor with unique physico-chemical properties. In this review, we summarize recent advances in the understanding of the fundamental properties and applications of excess electrons in reduced, undoped TiO2. We discuss the characteristics of excess electrons in the bulk and at the surface of rutile and anatase TiO2 focusing on their localization, spatial distribution, energy levels, and dynamical properties. We examine specific features of the electronic states for photoexcited TiO2, for intrinsic oxygen vacancy and Ti interstitial defects, and for surface hydroxyls. We discuss similarities and differences in the behaviors of excess electrons in the rutile and anatase phases. Finally, we consider the effect of excess electrons on the reactivity, focusing on the interaction between excess electrons and adsorbates. 相似文献
19.
E. Iguchi K. Ogino H. Sawatari R.J.D. Tilley 《Journal of Physics and Chemistry of Solids》1981,42(9):813-819
Dielectric constants and a.c. resistivities of rutile (TiO2) doped with gallia (Ga2O3) have been measured as a function of frequency in the range 30–60 kHz at 20°C. The specimens were prepared by heating rutile single crystals on Ga2O3 pellets, at 1300°C, in air for various times. The dielectric constants depend on the frequency of measurement. In the c axis, the dielectric constant at low frequencies (30–100 Hz) increases as the sample heating time is extended to 1 week, but it decreases rapidly when the heating time is prolonged over 1 week. However, in the a axis, the dielectric constant does not change from the value of the starting material, being independent of the heating time. Besides dielectric measurements, the defect structures were determined using transmission electron microscopy, which showed that low concentrations of planar faults on {120} planes occur. The changes in dielectric constant are interpreted as being due to space change effects associated with Ga3+ ions located in the tunnels which lie parallel to the rutile c axis. Calculations are also included which show why other defects in the crystals have no effect on the value of the dielectric constant compared to pure rutile. 相似文献
20.
R.A. Secco H. LiuN. Imanaka G. AdachiM.D. Rutter 《Journal of Physics and Chemistry of Solids》2002,63(3):425-431
Impedance spectroscopy measurements and synchrotron X-ray diffraction studies of Sc2(WO4)3 at 400°C have been carried out as a function of pressure up to 4.4 GPa. Ionic conductivity shows normal decrease with increase in pressure up to 2.9 GPa, but then increases at higher pressures. The XRD results show that Sc2(WO4)3 undergoes pressure-induced amorphization at pressures coincident with the reversal in conductivity behavior. The loss of crystal structure at high pressure is consistent with growing evidence of pressure-induced amorphization in negative thermal expansion materials, such as Sc2(WO4)3. The increase in conductivity in the amorphized state is interpreted as the result of an increase in structural entropy and a concomitant reduction of energy barriers for ionic transport. 相似文献