Raman spectroscopy of SrB<Subscript>4</Subscript>O<Subscript>7</Subscript> single crystals in the temperature range 300–1273 K

The polarized Raman spectra of SrB₄O₇ (SBO) single crystals are studied in detail in the temperature range of 300–1273 K. The TO, LO, and IO phonon lines of A₁, A₂, B₁, and B₂ symmetries of rhombic SBO at 300 K are identified. The behavior of the Raman spectra of SBO crystals is studied upon heating up to their melting. The relation of Raman spectra with the structure of boron–oxygen fragments, as well as the transformation of spectra in the process of melting of SBO crystals, is discussed.     

Raman spectroscopy of crystalline,glassy, and molten states of lead diborate

Polarized Raman spectra of single crystals of lead diborate, PbB₄O₇ (PBO), are studied in detail at 300 K. The TO-, LO-, and IO-phonon lines of the A ₁, A ₂, B ₁, and B ₂ symmetries in the Raman spectra of this compound are assigned. Changes in the Raman spectra of the internal vibrations of boron–oxygen complexes upon transition from the crystalline to the glassy and the molten states of PBO are observed. On the basis of the obtained results, the regularities in the formation of boron–oxygen complexes in glasses, melts, and crystals of the PbO · 2B₂O₃, SrO · 2B₂O₃, and Li₂O · 2B₂O₃. diborate compositions are analyzed.     

Polarized IR and Raman spectra,temperature dependence of phonons and lattice dynamic calculations for M′2M″Ge2O7 pyrogermanates (M′ = Sr,Ba; M″ = Mg,Zn)

Infrared and Raman spectra of the polycrystalline samples and single crystals of Sr₂ZnGe₂O₇, Ba₂ZnGe₂O₇, Ba₂MgGe₂O₇ and Sr₂MgGe₂O₇ were measured. The temperature dependence of phonons was studied in the range 4–295 K. The discussion of the results is based on the factor group approach for the tetragonal space group with Z = 2. The discussion of the internal vibrations of the Ge₂O₇ unit and external modes is made on the basis of the literature data and phonon calculations. The results obtained for the spontaneous Raman scattering were used in the discussion of the stimulated Raman spectra of the studied materials. Copyright © 2010 John Wiley & Sons, Ltd.     

PbB_4O_7晶体的太赫兹光谱和软光学声子

对实验测量的PbB4O7晶体样品的太赫兹(1012Hz)光谱、拉曼光谱以及红外—可见—紫外光谱进行了分析.在0.25—2.5THz波段介电函数随频率变化曲线ε(ν)出现共振型尖峰.四方面的分析表明PbB4O7晶体中存在软光学声子:1)介电函数随频率的变化曲线ε(ν)满足LST(Lyddane-Sachs-Teller)关系;2)在共振峰的频率附近(3.10THz)有很强的拉曼散射峰;3)吸收系数随频率的变化曲线α(ν)满足极化激元的特征;4)透过晶体的光子的色散关系ν(k)发生断开的畸变.PbB4O7晶体中存在软光学声子的意义在于,在满足产生极化激元的条件下,透过晶体的光子的频率会发生劈裂,分为升高和降低的两支,有可能利用这种原理来改变光子的频率.     

Polarized Raman and IR spectra of non‐centrosymmetric PbB4O7 single crystal

Polarized Raman and IR spectra of a PbB₄O₇ single crystal were measured. The obtained spectra are discussed within the factor group approach for the orthorhombic P2₁nm(C_2v⁷) space group with Z = 2 assuming that the crystal structure is built up of the (B₄O₇)_∞²⁻ framework and Pb²⁺ ions. It has been shown that vibrations of borate and Pb²⁺ units are observed above 240 and below 160 cm⁻¹, respectively. The results obtained for the spontaneous Raman scattering have also been used in the discussion of the stimulated Raman spectra of the material studied—a new Raman‐laser crystal. The obtained results revealed that mainly translational motions of Pb²⁺ ions participate efficiently in the SRS effect. Copyright © 2008 John Wiley & Sons, Ltd.     

Study of A-site doping of SrBi4Ti4O15 Bi-layered compounds using micro-Raman spectroscopy

The temperature-dependent Raman spectra of Mg- and La-doped SrBi₄Ti₄O₁₅ (SBT) were studied in the range 40–590 °C. A quantum chemistry calculation was employed to estimate these two substitution states. It was found that A-site doping in this study not only caused multiplicative substitution states, but also the Raman spectra changed with the substitution amount. In a La-doped perovskite-like layer, La would occupy the Bi site when x>0.10 and the 314 and 550 cm^-1 modes related to the rotating and tilting of the TiO₆ octahedron firstly became wide and then became sharp. With the increase of the substitution amount, both substitution states of Mg-doped SBT lead to the widening of 270 and 520 cm^-1 peaks. PACS 78.30.-J; 77.84.-s     

Birth of room‐temperature magnons and Raman line enhancement in ZnO nanostructures containing cobalt oxide

Cobalt (Co) addition and thermal annealing induced structural and vibrational properties of ZnO nanostructures were analysed. X‐ray diffraction pattern reveals that the nanostructures are in hexagonal wurtzite type and the formation of Co₃O₄. The Co ion induced morphology changes have been studied by high‐resolution scanning electron microscope images and energy dispersive spectroscopy measurements confirm the presence of Co ions. CoO‐related magnon excitation bands are emerged at room temperature for the Co‐added samples. There are no changes in the band positions of the Raman spectra of pure and Co‐added materials. Annealed sample exhibits the suppression of magnon bands and formation of Co₃O₄: ZnO composites. Raman line width and the electron phonon coupling constant are decreased with respect to the annealing temperature. The formation of Co₃O₄ : ZnO composite phases have further confirmed by infrared spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and characterization of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by high-energy milling and hydrothermal method

Spinel LiMn₂O₄ has been known to be a technologically important, environmental-friendly, and low-cost cathode material used in Li-based rechargeable batteries, and it is also widely available. Nanoparticle spinel LiMn₂O₄ has been synthesized by the top-down, high-energy milling, and hydrothermal methods. SEM images, X-ray diffraction patterns, and neutron high-resolution powder diffraction patterns have confirmed the nanocrystalline nature of the spinel LiMn₂O₄ samples. Raman and Fourier transform infrared (FTIR) measurements show typical absorption and vibration spectra typical for the spinel LiMn₂O₄ showing the formation of various metallic bonds in the sample. The strongest Raman and FTIR signals come from the higher frequency region, with weaker signals appearing in the lower frequency range.     

Characterization of partially inverse spinel ZnFe2O4 with high saturation magnetization synthesized via soft mechanochemically assisted route

ZnFe₂O₄ was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)₂/α-Fe₂O₃ and (2) Zn(OH)₂/Fe(OH)₃ mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe₂O₄ spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4 h of milling and its formation was completed after 18 h in both the cases of starting precursors. The synthesized ZnFe₂O₄ has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6 nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe₂O₄ powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion.     

The two-dimensional anharmonic oscillator: The CCC bending mode of C3O2

Newly observed data on the rotational constants of carbon su?ide in excited vibrational states of the low-wavenumber bending vibration ν₇ have been successfully interpreted in terms of the two-dimensional anharmonic oscillator wavefunctions associated with this vibration. By combining these results with published infrared and Raman spectra the vibrational assignment has been extended and a refined bending potential for ν₇ has been derived: this has a minimum at a bending angle of about 24° at the central C atom, with an energy maximum at the linear configuration some 23 cm^?1 above the minimum. From similar data on the combination and hot bands of ν₇ with ν₄ (1587 cm^?1) and ν₂ (786 cm^?1) the effective ν₇ bending potential has also been determined in the one-quantum excited states of ν₄ and ν₂. The effective ν₇ potential shows significant changes from the ground vibrational state; the central hump in the ν₇ potential surface is increased to about 50 cm^?1 in the v₄ = 1 state, and decreased to about 1 cm^?1 in the v₂ = 1 state. In the light of these results vibrational assignments are suggested for most of the observed bands in the infrared and Raman spectra of C₃O₂.     

Vibrational spectrum of Li2B4O7 crystals

The polarized infrared reflection spectra of Li₂B₄O₇ were studied in the spectral range 80–1600 cm^?1 and compared with Raman spectra. From the spectrum dispersion analysis, the frequencies, damping, and dielectric oscillator strengths were determined for all vibrational modes observed. A calculation of the effective charges and an analysis of the chemical-bond types of the Li₂B₄O₇ crystal structural units were carried out on the basis of the obtained data.     

Neutron Spectroscopy of the Atomic Dynamics of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> at Fluorite–Pyrochlore Structural Transformations

The formation of the structural and dynamic properties of La₂Zr₂O₇ in the process of crystallization at the isothermal annealing of initially amorphous precursors obtained by the coprecipitation of corresponding salts has been studied by neutron spectroscopy. The existence of vibrational states characteristic of hydrogen, which is in one or another of the possible chemical states and is incorporated into a solid matrix, has been detected in the spectra of amorphous and fluorite phases. The DFT calculation of the phonon density of states has been performed to analyze the energy structure of experimental phonon spectra for various phases of the La₂Zr₂O₇ compound. The amount of hydrogen in the fluorite phase has been estimated.     

Electron energy loss spectra and X-ray photoelectron spectra of Ca2V2O7

We have measured the electron energy loss spectra of Ca₂V₂O₇ in the reflexion mode, at incident energies between 200 and 2400 eV, and the X-ray photoelectron spectra excited by Al K α radiation. The abundant loss structures observed can be correlated with the possible interband transitions, collective oscillations, and excitation of O2s and V3p electrons within the V₂O₇^4- ion. The gap width and molecular orbital (MO) spread (or splitting) is about l eV larger in the V₂O₇^4- ion than in its component VO₄^3- ion. Excitation of O2s states, which may occur together with some MO over-gap transitions, displaces the collective oscillations about 7 eV towards lower energies. Deeper V3p electrons are excited with a maximum energy loss some 7 eV above their binding energy. Cross transitions from Ca3p levels into some empty states of the V₂O₇^4- ion, or direct transitions to available states of the Ca²⁺ ion could not be unambiguously identified. The energy dependence of the excitation cross section and of the electron penetration depth results in a significant variation of the relative intensity of various losses over the investigated energy range.     

Raman spectra of polycrystalline bismuth titanate nanotubes

The Raman spectra of bismuth titanate Bi₄Ti₃O₁₂ nanotubes synthesized by the template method on an Al₂O₃ membrane have been studied. The samples prepared represent an array of oriented ∼50-μm-long nanotubes with coalescing smooth walls. The nanotube wall thickness is varied from 20 to 50 nm, and the nanotube inside diameter is about 200 nm. The Raman spectra of the nanotubes demonstrate a broadening of the lines corresponding to the stretching and bending vibrations of TiO₆ octahedra. In the low-frequency spectral range corresponding to vibrations of Bi ions with respect to the oxygen octahedra, a transformation due to strong mechanical stresses generated during the formation of the nanotubes has been observed.     

Preparation of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowires by calcining the precursor powders synthesized in a novel inverse microemulsion

Manganese oxide (hausmannite) nanowires were prepared by annealing precursor powders at a temperature of 800 °C for 3 h, which were produced in a novel inverse microemulsion (IμE) system. The microstructures of the as-prepared Mn₃O₄ nanowires were investigated by means of X-ray diffraction, transmission electron microscopy, and Raman spectra. It has been found that the Mn₃O₄ nanowires were relatively straight and their surfaces were smooth with a typical diameter of 75–150 nm. The formation mechanism of the Mn₃O₄ nanowires is discussed. Received: 30 May 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn     

Temperature‐dependent Raman scattering studies of the geometrically frustrated pyrochlores Dy2Ti2O7, Gd2Ti2O7 and Er2Ti2O7

The temperature‐dependent Raman studies of A₂Ti₂O₇(A = Dy, Er, Gd) were performed on single crystals and polycrystalline samples in the 4.2–295 K temperature range. The Raman spectra showed softening of the majority of phonon modes upon cooling in the whole temperature range studied and large decrease of linewidths. These changes have been analyzed in terms of strong third‐order phonon–phonon anharmonic interactions. Moreover, the 312 and 330 cm⁻¹ modes of Er₂Ti₂O₇(Gd₂Ti₂O₇) showed hardening upon cooling down to about 130 K (100 K) and then anomalous softening below this temperature. The observed anomalous behavior of the Raman modes indicates that some important changes occur in these materials at low temperatures. However, the origin of this behavior is still not clear. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectrum of Li2B4O7 crystals

Polarized IR reflection spectra of Li₂B₄O₇ crystals are studied in a spectral range of 80–1600 cm^?1 and compared with their Raman spectra. Based on the results of the dispersion analysis of the spectra, the frequencies, damping constants, and oscillator strengths of all vibrations are determined. The inversion of frequencies of the longitudinal and transverse vibrations of the A ₁ and E symmetry in a range of 900–1150 cm^?1 is found. Based on the data thus obtained, the effective charges are calculated and the types of chemical bonds are analyzed for structural groups of the Li₂B₄O₇ crystal.     

Surface‐enhanced Raman scattering of 4‐mercaptopyridine on sub‐monolayers of α‐Fe2O3 nanocrystals (sphere,spindle, cube)

We report surface‐enhanced Raman scattering (SERS) spectra from 4‐mercaptopyridine (4‐Mpy) adsorbed on sub‐monolayers of α‐Fe₂O₃ nanocrystals (sphere, spindle, cube). The maximum enhancement factor has been estimated to be about 10⁴ compared to that of 4‐Mpy in solution. A possible mechanism has been proposed that the charge transfer between the α‐Fe₂O₃ nanocrystals and the 4‐Mpy molecules is most likely responsible for the observed enhancement of Raman intensity of adsorbed 4‐Mpy molecules as surface plasmon resonances have not occurred. Copyright © 2009 John Wiley & Sons, Ltd.     

Observation of resonance electronic and non‐resonance‐enhanced vibrational natural Raman optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low‐lying electronic transition is reported. These new phenomena were measured using the rare‐earth complex Eu(tfc)₃ (+)‐tris[3‐trifluoroacetyl‐D ‐camphorato]europium(III), where electronic resonance occurs between the 532‐nm laser excitation and the ⁷F₁ → ⁵D₁ transition of the Eu³⁺ metal center. Electronic Raman spectra involve the Raman transitions terminating on the low‐lying electronic states of Eu(tfc)₃. The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)₃ to its low‐lying electronic states with significant magnetic‐dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance‐enhanced since the 532‐nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064‐nm laser excitation. Copyright © 2010 John Wiley & Sons, Ltd.     

A temperature dependence Raman study of the 0.1Nb2O5-0.9TeO2 glass-forming system

Raman spectra of the 0.1Nb₂O₅-0.9TeO₂ binary glass-forming oxide system were measured over a temperature range including the glassy, supercooled and crystalline state to reveal the structural changes caused by temperature variation. The analysis of the reduced Raman spectra made it possible to quantitatively follow the transformation of the TeO₄ trigonal bipyramids—that dominate in the low temperature glass—into TeO₃ trigonal pyramids with temperature rise. Based on the predictions of existing structural models, we estimated with the aid of the Raman data the number of terminal oxygen atoms that inevitably accompany this structural change. The various crystal phases of the system studied in this work and the routes for converting one crystal phase into another were also examined. Finally, the low-energy excitations of the non-crystalline states of 0.1Nb₂O₅-0.9TeO₂ were studied by following the temperature dependence of the Boson peak.