Surface structure of TiO2(011)-(2x1)

A combined experimental and first principles study of the (2x1)-reconstructed rutile TiO2(011) surface is presented. Our results provide evidence that the surface structure is described by a model that includes onefold coordinated (titanyl) oxygen atoms giving rise to double bonded Ti=O species. These species should play a special role in the enhanced photocatalytic activity of the TiO2(011) surface.     

(Ta_2O_5)_(1-x)(TiO_2)_x陶瓷结构相变研究

采用固相反应技术制备了x分别为 0 0 5、0 0 8和 0 1 1的 (Ta2 O5) 1-x(TiO2 ) x 陶瓷 ;在室温至 6 0 0℃范围内 ,测量了这些陶瓷样品的拉曼光谱随温度的变化。随着温度的升高 ,拉曼光谱中位于 35～38cm- 1的最低频移的声子模发生软化 ,并随之发生结构相变。拉曼光谱和实验结果都表明 :组分x分别为0 0 5、0 0 8和 0 1 1的 (Ta2 O5) 1-x(TiO2 ) x 陶瓷分别在 36 0、4 5 0和 5 4 0℃发生了由三斜至单斜相的结构相变。上述结论得到了 (Ta2 O5) 0 92 (TiO2 ) 0 0 8单晶热膨胀系数测量数据的支持。     

Revised superconducting phase diagram of hole-doped Na(x)(H3O)(z)CoO2 x yH(2)O

We have studied the superconducting phase diagram of NaxCoO2.yH(2)O as a function of electronic doping, characterizing our samples both in terms of Na content x and the Co valence state. Our findings are consistent with a recent report that intercalation of H3O+ ions into NaxCoO2, together with water, acts as an additional dopant, indicating that Na substoichiometry alone does not control the electronic doping of these materials. We find a superconducting phase diagram where optimal T(C) is achieved through a Co valence range of 3.24-3.35, while T(C) decreases for materials with a higher Co valence. The critical role of dimensionality in achieving superconductivity is highlighted by similarly doped nonsuperconducting anhydrous samples, differing from the superconducting hydrate only in interlayer spacing.     

Structure of the rutile TiO2(011) surface in an aqueous environment

First principles simulations are carried out to investigate the structure and stability of the rutile TiO2(011) surface in contact with liquid water. Whereas this surface exhibits a (2×1) reconstruction in vacuo, our results show that the interaction with water leads to an inversion of the stabilities of the reconstructed and unreconstructed surfaces. This indicates that surface structures determined in vacuo or at low water coverages are not generally representative of those occurring in the aqueous environments typical of most photocatalytic applications of TiO2.     

Electrical second harmonic generation by (Pb x -Ba1−x )TiO3 and (Pb x -Sr1−x )TiO3 in the autostabilized state

The temperature autostabilizing nonlinear dielectric element (TANDEL) effect and second harmonic generation have been studied in the ferroelectric solid solutions of (Pb _x -Ba_1−x )TiO₃ and (Pb _x -Sr_1−x )TiO₃ near the Curie temperature used as TANDEL. The generated second harmonics are linear for low d.c. biasing fields with zero off-set while they decrease sharply at higher d.c. biasing fields. The results show that these solid solutions might be used as TANDEL elements.     

Structure determination of the two-domain ( 1x4) anatase TiO2(001) surface

The reconstructed anatase TiO2(001) surface has been investigated by low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and angle-resolved mass spectroscopy of recoiled ions (AR-MSRI). Prior investigations have observed or considered only a (1x1) unreconstructed termination for this surface with no detailed structural analysis. Our LEED results indicate a previously unobserved two-domain (1x4) reconstruction after sputtering and annealing the (1x1) surface. The XPS data for this reconstruction indicate the presence of only Ti4+. Simulations of the AR-MSRI experimental data indicate a best fit for a microfaceted surface, revealing both (103) and (1;03) surface planes.     

Evolution of the electronic structure of 1T-Cu(x)TiSe(2)

The electronic structure of a new charge-density-wave system or superconductor, 1T-Cu(x)TiSe(2), has been studied by photoemission spectroscopy. A correlated semiconductor band structure is revealed for the undoped case, which resolves a long-standing controversy in the system. With Cu doping, the charge-density wave is suppressed by the raising of the chemical potential, while the superconductivity is enhanced by the enhancement of the density of states, and possibly suppressed at higher doping by the strong scattering.     

Optical Properties of the (CuInSe2) x ·(2ZnSe)1−x and (CuInTe2) x (·2ZnTe)1−x Solid Solutions

Crystals of the compounds CuInSe₂, CuInTe₂, ZnSe, and ZnTe, and the solid solutions (CuInSe₂) _x ·(2ZnSe)_1–x and (CuInTe₂) _x ·(2ZnTe)_1–x were grown by the Bridgman and chemical transport reactions methods. Their transmission and reflection spectra in the region of the main absorption line edge were studied. The forbidden band gap of the indicated materials was determined and its concentration dependences were built for the solid solutions. It is established that the forbidden band gap changes linearly with the x composition and is satisfactorily described by the square-law dependence.     

激光烧结(Ta_2O_5)_(1-x)(TiO_2)_x陶瓷的拉曼光谱研究

简介了激光快速烧结陶瓷技术;测量了采用激光快速烧结技术和传统电炉烧结技术制备的(Ta2O5)1-x(TiO2)x陶瓷的相对介电常数和介电损耗;分析了这两类试样的激光拉曼光谱和粉末XRD谱;发现:(Ta2O5)1-x(TiO2)x陶瓷经激光快速烧结后产生了新相,从而导致相对介电常数大幅度提高。     

Atomic structure of a (2 x 1) reconstructed NiSi2/Si(001) interface

Nickel disilicide/silicon (001) interfaces were investigated by aberration corrected scanning transmission electron microscopy (STEM). The atomic structure was derived directly from the high spatial resolution high angle annular dark field STEM images without recourse to image simulation. It comprises fivefold coordinated silicon and sevenfold coordinated nickel sites at the interface and shows a 2 x 1 reconstruction. The proposed structure has not been experimentally observed before but has been recently predicted theoretically by others to be energetically favored.