Defects in scandium doped barium zirconate studied by Sc-45 NMR

Local structure around Sc in BaZr_1 − xSc_xO_3 − δ protonic conductor has been investigated by ⁴⁵Sc MAS-NMR. The MAS-NMR spectra were consisted of several peaks, which can be assigned to Sc in different coordination environment. Compositional dependence of the spectrum was observed. The coordination environment of Sc is determined from the peak deconvolution, and the oxygen vacancy concentration and the protonic defect concentration around Sc were obtained. The present investigation suggests that oxygen vacancies preferentially located around Sc and the concentration of oxygen vacancies in the vicinity of Sc increases with increasing the Sc content. Protonic defects were found to be preferentially located around Sc at lower Sc content.     

Preparation, characterization and study of optical properties of ZnS nanophosphor

In this work the preparation, characterization and photoluminescence studies of pure and copper-doped ZnS nanophosphors are reported, which are prepared by using solid-state reaction technique at a temperature of 100 °C. The as-obtained samples were characterized by X-ray diffraction (XRD) and UV-VIS Reflectance spectroscopy. The XRD analysis confirms the formation of cubic phase of undoped as well as Cu²⁺-doped ZnS nanoparticles. Furthermore it shows that the average size of pure as well as copper-doped samples ranges from 15 to 50 nm. The room-temperature PL spectra of the undoped ZnS sample showed two main peaks centered at around 421 and 450 nm, which are the characteristic emissions of interstitial zinc and sulfur vacancies, respectively. The PL of the doped sample showed a broad-band emission spectrum centered at 465 nm accompanied with shoulders at around 425, 450 and 510 nm, which are the characteristic emission peaks of interstitial zinc, sulfur vacancies and Cu²⁺ ions, respectively. Our experimental results indicate that the PL spectrum confirms the presence of Cu²⁺ ions in the ZnS nanoparticles as expected.     

Local structure analysis of YSZ by Y-89 MAS-NMR

The local coordination structure around Yttrium ions in yttria stabilized zirconia (YSZ) has been investigated by ⁸⁹Y MAS-NMR. The NMR spectrum showed multiple peaks corresponding to yttrium ions in different coordination numbers. The compositional dependence of spectra was observed. Yttrium ions of different oxygen coordination number were quantified. The oxygen vacancy concentration around the cations was determined. It was found that the vacancies were distributed around Zirconium ions in lower Y₂O₃ concentrations, and the vacancy concentration located to Yttrium began increasing at concentrations above 10 mol% Y₂O₃. The local structure change was able to be directly observed by ⁸⁹Y NMR measurements.     

Intrinsic defect related luminescence in ZrO2

The studies of ZrO₂ and yttrium stabilized ZrO₂ nanocrystals luminescence as well as yttrium stabilized single crystal luminescence and induced absorption showed that the intrinsic defects are responsible for luminescence at room temperature. These defects form a quasi-continuum of states in ZrO₂ band gap and are the origin of the luminescence spectrum dependence on the excitation energy. Luminescence centers are oxygen vacancies related but not the vacancies themselves. At room temperature, in ZrO₂, deep traps for electrons and holes exist. The oxygen vacancies are proposed to be the traps for electrons.     

单相钇钡铜氧高温超导体的超导转变与内耗原位研究

在80至300K温度范围内对YBa₂Cu₃O_7-δ高温超导体的电阻、内耗和弹性模量随温度的变化进行了原位测量。在T_c附近观察到两个明显的内耗峰。从峰的特征推断,这两个内耗峰可能与电子在Cu³⁺与Cu²⁺之间的弛豫过程有关。而在160K到280K温度范围内所观察到的内耗峰及杨氏模量反常效应,可能与试样中氧空位的调整有关。 关键词：     

Synthesis of In-doped Ga2O3 zigzag-shaped nanowires and optical properties

In-doped Ga₂O₃ zigzag-shaped nanowires and undoped Ga₂O₃ nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In₂O₃ and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

Oxygen vacancy in LiTiPO5 and LiTi2(PO4)3: A first-principles study

The structures of LiTiPO₅ and LiTi₂(PO₄)₃, as well as the possibility of oxygen vacancies formation in the systems are studied by first-principles calculations. It is found that oxygen vacancies can be formed in LiTiPO₅ and LiTi₂(PO₄)₃ under oxygen poor condition. The formation of oxygen vacancies introduce a defect band within their band gaps, which is expected to improve the electronic conductivity of LiTiPO₅ and LiTi₂(PO₄)₃ significantly. Meanwhile, a great concentration of oxygen vacancies may increase the discharge voltage of LiTiPO₅ and LiTi₂(PO₄)₃.     

Electronic Structure of Oxygen Vacancies in the Orthorhombic Noncentrosymmetric Phase Hf<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript>

The electronic structure of stoichiometric and oxygen-depleted Hf_0.5Zr_0.5O₂ in the orthorhombic noncentrosymmetric phase has been studied by X-ray photoelectron spectroscopy and quantum-chemical simulation based on the density functional theory. It has been established that the ion-etching-induced peak in the photoelectron emission spectrum with the energy above the top of the o-Hf_0.5Zr_0.5O₂ valence band is due to oxygen vacancies. A method of estimating the density of oxygen vacancies from the comparison of the experimental and theoretical photoelectron spectra of the valence band has been proposed. It has been established that oxygen polyvacancies in o-Hf_0.5Zr_0.5O₂ are not formed: the energetically favorable spatial arrangement of oxygen vacancies in a crystal corresponds to noninteracting oxygen vacancies distant from each other.     

Preparation and structural characterization of nanocrystalline SnO2 powders

Nanocrystalline SnO₂ powders have been prepared by solid–liquid reaction and solid-state thermal oxidizing techniques. The microstructures and phase compositions of the product were characterized by thermogravimetry analysis, X-ray diffraction, and the Raman spectrum. It is shown that at least two phases, SnO₂ and SnO_x, coexist at 450 °C. However, only the tetragonal rutile structure SnO₂ phase is detected after the Sn powders were annealed at 550 °C. The Raman peaks of the nanocrystalline SnO₂ powders reveal remarkable red shift and broadening, which could be attributed to the phonon confinement effect, oxygen vacancies, and the stress effect. PACS 81.07.Wx; 81.10.Jt; 78.30.-j     

双模腔场中两偶极相互作用原子的辐射谱

研究了双模腔场中两个偶极相互作用原子的辐射谱，详细讨论了双模腔场分别处于不同数态时的情形，发现其辐射谱具有如下特点：当两模腔场均处于真空态时，随着δ＝ｇ_a／ｇ的增加，辐射谱交替出现六峰、五峰结构，且在δ（＝３^－１／２）很小时就出现了非对称五峰结构，与单模双原子情形相比较，更为灵敏地反映出原子间的偶极相互作用；当一腔场为真空场，另一腔场为强场时，辐射谱显示出对称的六峰结构，任意两对称峰的间距与(2ｎ₂)^１／２ｇ成正比；当 关键词：     

Experimental investigation of angular dependence of photon induced L-shell X-ray emission intensity

The angular dependence of emission intensity of L shell X-rays induced by 59.57 keV photons in Pb and U is investigated by measuring the normalized intensities of the resolved L X-ray peaks at different angles varying from 40° to 120°. It is observed that while L _l and L_α X-ray peaks (originating fromJ = 3/2 state) show some anisotropic angular distribution, the emission of L_β and L_γ X-ray peaks is isotropic. The present results contradict the calculations of Co-oper and Zare (1969) that after photoionization of inner shell, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic but confirm the predictions of Fluggeet al (1972) that the atomic inner shell vacancies produced after photoionization are aligned and the x-ray emission from the filling of vacancies in state withJ ⩾ 3/2 is anisotropic.     

Vacancy induced changes in the electronic structure of titanium carbide—I. Band structure and density of states

Results of a self-consistent “Augmented Plane Wave” (APW) band-structure calculation are presented for substoichiometric titanium carbide with 25% vacancies on the carbon sublattice sites (TiC_{0 75}) assuming a model structure with ordered vacancies Comparison with an earlier APW study on stoichiometric TiC reveals that the carbon vacancies induce two pronounced peaks in the density of states (DOS), 0.4 eV below and 0.8 eV above the Fermi energy E_γ, thus forming electronic states in a region where the DOS for stoichiometric TiC exhibits a minimum So-called “vacancy states” with an important amount of charge on the vacancy site are found to be derived from Ti 3d states extending into the vacancy muffin tin sphere An angular momentum decomposition with respect to the center of the vacancy muffin tin sphere shows that the s character predominates for the occupied and the p character for the unoccupied “vacancy states” The theoretical findings explain features near E_γ, observed in recently published X-ray emission spectra Furthermore, we find a slight increase of electronic charge in the carbon muffin tin spheres as compared with stoichiometnc TiC.     

Deep levels of intrinsic point defects and the nature of “anomalous” optical absorption in ZnGeP2

Deep levels of single vacancies and antisite defects in the structure of the ZnGeP₂ compound are investigated using the pseudopotential method and an extended unit cell. The data obtained are compared with those for the GaP isoelectronic analog. It is demonstrated that, in the case of the ZnGeP₂ crystal, deep levels (degenerate in the GaP structure) are substantially split as a result of lowering the lattice symmetry and anisotropy of the chemical bonding. In particular, the splitting of the V _P ⁰ (t ₂) level is equal to 1.58 eV. The averaged levels of defects in the ZnGeP₂ compound are in close agreement with the levels of defects in the GaP compound. The absorption coefficients for polarized light are calculated with allowance made for the neutral and charged states of the defects. The optical transitions responsible for the absorption peaks in the IR range of the spectrum of the ZnGeP₂ compound are revealed. It is shown that the first peaks are associated with the transitions of electrons from the valence band states located deep in the Brillouin zone to the V _Zn ^?1 and V _P ⁰ deep levels. This leads to a considerable shift (by ～0.3 eV) of these peaks toward the high-energy range as compared to the energy positions of the deep levels in the band gap with respect to the top of the valence band. The experimental data on the photoinduced EPR spectra of postgrowth and electron-irradiated ZnGeP₂ crystals are consistently interpreted by analyzing the electron density.     

LOW-FREQUENCY INTERNAL FRICTION STUDY ON MODIFIED LEAD METANIOBATE CERAMICS

Six Q^-1 peaks in freshly-worked PbNb₂O₆ ceramics are observed by low-frequency internal friction measurement so far as we know for the first time. P₁, P₂, and P₄ appear at the first heating process with remarkable shear modulus anomalies. But they are not observed during the cooling process or in the well-annealed samples. Those peaks are considered to be related with the working processes. P₃ is a widened Debye relaxation peak in nature. The activation energy and pre-exponential factor are about 1.01 eV and 2.5×10^-12 s, respectively. This peak is attributed to the interaction of domain walls and oxygen vacancies. P₆ is corresponded with the paraelectric and ferroelectric phase transition. P₅, appearing near T_c, is thought to be caused by the viscous movement of the domain walls.     

衬底温度对PLD法生长的Mg0.05Zn0.95O薄膜结构和发光特性的影响

用脉冲激光沉积(PLD)法在不同温度的Si(111)衬底上成功制备了c轴择优取向的Mg_005Zn_095O薄膜.通过X射线衍射(XRD)和光致发光谱(PL)研究了衬底温度对Mg_005Zn_095O薄膜结构和发光特性的影响,探讨了薄膜的结晶质量与发光特性之间的关系.结果表明,在衬底温度为450℃时生长的Mg_005Zn_095O薄膜具有很好的c轴取向和较强的光致发光峰.室温下分别用激发波长为240,300和325nm的氙灯作为激发光源得到不同样品的PL谱,分析表明紫外发光峰和紫峰来源于自由激子的复合辐射且发光强度与薄膜的结晶质量密切相关,蓝绿发光峰与氧空位有关.此外,探讨了衬底温度影响紫外光致发光峰红移和蓝移的可能机理. 关键词： 005Zn_095O薄膜')" href="#">Mg_005Zn_095O薄膜 PLD 衬底温度 光致发光     

The Auger electron spectrum of carbon suboxide (C3O2)

The high resolution KLL Auger electron spectrum of carbon suboxide (C₃O₂) in gas form, has been recorded. Assignments, assisted by intensity and energy calculations, are proposed for the peaks in the spectrum. A comparison is made with the oxygen Auger spectrum of CO. The ground state energy of the doubly charged C₃O₂ ion is found to be 29.7 eV.     

China rose petal as biotemplate to produce two-dimensional ceria nanosheets

China rose petal was used as robust biotemplate for the facile fabrication of novel ceria nanosheet with a thickness of about 7 nm via a continuous infiltration process. The presence of well-resolved peaks ([111], [200], [220], and [311]) for the products revealed the formation of the fluorite-structured CeO₂. The detailed characterization by field-emission scanning electron microscope (FESEM), field-emission transmission electron microscope (FETEM), and atomic force microscopy (AFM) exhibited the biomorphic structure of polycrystalline ceria film with the nanoparticle size of ca. 6.98 nm. Based on the surface chemistry and biochemistry processes, a possible mechanism for the formation of CeO₂ nanosheets is proposed. Furthermore, nitrogen adsorption–desorption measurement and photoluminescence spectrum (PL) were employed to characterize the samples. The ceria nanosheet showed the existence of mesopores (pores 2–4 nm diameter) on its surface and a broad emission ranging from 350 to 500 nm in photoluminescence spectrum. X-ray photoelectron spectroscopy analysis (XPS) confirmed that the mesoporous nanosheets possessed more surface vacancies than the bulk CeO₂; hence these hierarchical CeO₂ layers appear to be potential candidates for catalytic applications.     

Properties of Ga2-X-Te3 investigated by129I Mössbauer spectroscopy

¹²⁹I Mössbauer spectroscopy was used to study the properties of^129mTe labeled Ga₂Te₃. and alloyed (Ga₂Te₃)_xAu_y and (Ga₂Te₃)_xAs_y, sources. A satisfactory fit to the Ga₂Te₃ spectrum could only be obtained by introducing a distribution in the hyperfine interaction parameters. This is interpreted in favor of the hypothesis of a random distribution of the structural vacancies in the deficit cubic Ga₂Te₃. The addition of atomic percents of As to the compound did not change significantly the pure Ga₂Te₃ spectrum. The spectrum of Ga₂Te₃ alloyed with atomic percents of Au, on the contrary, could be fitted with only one component with a satisfactory narrow linewidth, suggesting that due to Au doping ordering is induced in the stoichiometric vacancies of the Ga₂Te₃ lattice structure.     

快冷Fe-Al合金中的原子缺陷弛豫

在多功能内耗仪上用自由衰减和强迫振动方法研究了不同Al含量淬火Fe-Al合金中的两个弛豫型内耗峰.结果显示：P1(180℃)和P2(340℃)两个内耗峰只出现在淬火样品的加热过程中,而在随后的冷却过程中不出现.P1峰是由在α和β(或γ)点阵上的空位组成的最近邻双空位偶极子在应力诱导下的重新取向产生的,其弛豫强度随Al含量非单调地变化,在大约25% Al(原子百分比,以下同)处出现最大值.Al含量较低的Fe-Al合金无 关键词： 空位 弛豫 Al含量     

Optical characteristics of amorphous V2O5 thin films colored by an excimer laser

The V₂O₅ films were prepared by an RF sputtering method, and the amorphous films were colored by an UV excimer laser. The crystallinity of the as-grown V₂O₅ film was degenerated greatly by laser irradiation, as determined by X-ray diffraction (XRD) and Raman studies. The transmission and complex refractive index spectra of the V₂O₅ film were affected by variations in the microstructure, including the surface morphology, crystalline structure, and substoichiometry with an oxygen deficiency. Considerable emissions due to oxygen vacancies and band transition of photoluminescence (PL) peaks were observed, and the peaks were significantly changed after laser irradiation. The variations in the optical properties in both films may be attributed to oxygen deficiency induced by laser irradiation.