六方晶型MgTiO3温致微结构变化及其原位拉曼光谱研究

采用固相烧结法制备了六方晶型结构的MgTiO₃粉体. 经高温原位X射线衍射分析(293-1473 K)进行了表征与确认,获得了晶胞参数及其随温度的变化,测量了高温原位拉曼光谱(273-1623 K),并运用第一性原理理论计算方法对应核实了拉曼谱峰的归属. 结果表明,随着温度升高,MgTiO₃晶面间距和晶格常数增大,从而反映对于拉曼光谱较为敏感的键长和键角的变化;温致拉曼位移可以反映Ti-O,Mg-O等键长以及Ti-O-Ti,Ti-O-Mg与Mg-O-Mg等键角随温度的细微变化,相关关系则独立于温度,有效提升了原位拉曼光谱微探针诊断技术的分析能力;拉曼谱峰随温度升高而展宽,表明原子瞬间运动振幅加剧,弥散性增加,稳定性有所下降,但仍维持六方晶型. 关键词： 3')" href="#">MgTiO₃ 微结构 拉曼光谱 高温     

Raman scattering study of GeTe and Ge2Sb2Te5 phase-change materials

Structural details of the amorphous binary GeTe and ternary Ge₂Sb₂Te₅ (GST) phase-change materials are investigated with the aid of Raman scattering. In the case of the a-GeTe, a plethora of Raman bands have been recorded and assigned on the basis of a network structure consisting of corner- and edge-sharing tetrahedra of the type GeTe_4−nGe_n (n=0, 1, 2, 3, 4). Significant temperature-induced structural changes take place in this material even at temperatures well below the crystallization temperature. These changes tend to organize the local structure, in particular the coordination number of Ge atoms, so as to facilitate the amorphous-to-crystal transformation. The much simpler Raman spectrum of GST, characterized by one vibrational band, is accounted for by the dominance of the Sb₂T₃ component in Raman scattering; reasons about this explanation, as well as for the lack of any Te–Te bonds are briefly described.     

Fine band structure of the vibrational spectra of fullerite C<Subscript>60</Subscript> and enhancement of intermolecular interaction in high-temperature phase

The fine structure of the fundamental vibrational bands and some combination tones of fullerite C₆₀ in its IR absorption and reflection spectra, as well as in Raman spectra, has been studied. This structure is due to the overlapping components of Davydov and isotopic splittings and the removal of vibrational degeneracy with symmetry lowering. It is shown that for IR F _u (i) bands (i = 1–4) and low-frequency H _g (1) and A _g (1) bands in the Raman spectrum the splittings at room temperature exceed those for the low-temperature phase. The enhancement of intermolecular interaction at elevated temperatures is explained by the nonequilibrium vibrational excitation of the medium as a result of nonlinear interaction of vibrational modes and by the change in the electronic states.     

Vibrational spectroscopic studies,conformations and ab initio calculations of 1,2‐bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3)

Infrared spectra of 1,2‐bis(trifluorosilyl)ethane (SiF₃CH₂CH₂SiF₃) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers (anti and gauche) in the vapour, liquid and in the matrix. When the vapour was chock‐frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C_2h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave ΔH(gauche—anti) = 5.6 ± 0.5 kJ mol⁻¹ in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low‐energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS‐QB3 and in G3 calculations was 5 kJ mol⁻¹. Copyright © 2009 John Wiley & Sons, Ltd.     

Cr3+−Cr3+ excited state Raman scattering from molecular vibrations in binuclear Cs3Cr2Cl9 induced by exchange striction

On increasing the temperature, several new bands appear at higher energy from their parent vibrational modes in the Raman spectrum of the molecular complex Cr₂Cl^3?₉. The parent and new bands have intensities that follow the thermal population factors of various ⁴A_2g⁴A_2g Cr³⁺ pair states. This behaviour is attributed to exchange striction which produces a change in vibrational energy with excited state for those normal modes with large net axial Cr³⁺?Cr³⁺ displacements.     

Raman spectroscopy of RuSr2(Eu1.5Ce0.5)Cu2O10 magneto-superconductor

Raman spectroscopy studies are reported for the RuSr₂Eu_1.5Ce_0.5Cu₂O₁₀ (Ru-1222) compound at various temperatures of 300, 250, 200 and 90 K. Three distinct vibrational bands: the first at 110, 140, and 160 cm⁻¹, the second at 295 and 347 cm⁻¹, and third one at 651 cm⁻¹ are seen in Raman spectra of the compound at room temperature. These bands are attached to the Cu atoms’ c-direction, the Ru atoms’ ab-plane stretching and Ru atoms’ c-direction anti-stretching modes. Below 200 K, an extra vibrational mode is also seen at 260 cm⁻¹. Also, with a decrease in temperature, though the Cu vibrational modes remain intact, the Ru atoms’ ab-plane stretching (295 cm⁻¹) and c-direction anti-stretching (651 cm⁻¹) modes shift gradually to higher wave number positions. The frequencies of modes at 260 and 651 cm⁻¹ showed anomalous softening and line-width broadening below 100 K that corroborates well with the spin ordering seen in susceptibility studies. The studied compound is a ferromagnetic superconductor with magnetic ordering of the Ru spins at 200 K and superconductivity below 30 K. A magnetic and electrical transport characterization of the compound is also presented briefly.     

Phonon spectrum and interaction between nanotubes in single-walled carbon nanotube bundles at high pressures and temperatures

The Raman spectra of single-walled carbon nanotubes at temperatures up to 730 K and pressures up to 7 GPa have been measured. The behavior of phonon modes and the interaction between nanotubes in bundles have been studied. It has been found that the temperature shift of the vibrational G mode is completely reversible, whereas the temperature shift of radial breathing modes is partially irreversible and the softening of the modes and narrowing of phonon bands are observed. The temperature shift and softening of radial breathing modes are also observed when samples are irradiated by laser radiation with a power density of 6.5 kW/mm². The dependence of the relative frequency Ω/Ω₀ for G ⁺ and G ^? phonon modes on the relative change A ₀/A in the triangular lattice constant of bundles of nanotubes calculated using the thermal expansion coefficient and compressibility coefficient of nanotube bundles shows that the temperature shift of the G mode is determined by the softening of the C-C bond in nanotubes. An increase in the equilibrium distances between nanotubes at the breaking of random covalent C-C bonds between nanotubes in bundles of nanotubes is in my opinion the main reason for the softening of the radial breathing modes.     

First principles study of structural, electronic and vibrational properties of heavily boron-doped diamond

The structural, electronic and vibrational properties of a series of heavily B-doped diamond models have been investigated using the density functional theory within a local density approximation. The doped models C_64 − nB_n (n=1-3) were constructed using supercell techniques. The structural and electronic calculations confirmed that the B dimers are always energetically stable and electrical inactive. The superconducting transition temperature TC is not only decided by the B concentration, but also by the lattice configurations of boron atoms. The vibrational frequencies and eigenmodes were determined using the linear response approach, while Raman intensities were obtained by the second response method. The Raman analysis in terms of atomic vibrations found that the “500 cm⁻¹” and “1230 cm⁻¹” bands are both superposed bands including not only C vibrations but also B-B vibrations and B-C vibrations, respectively. The calculated Raman spectra with isotopic substitutions are in excellent agreement with corresponding experimental results. The reasonable explanation was provided for no obvious Raman shift of main bands from ¹⁰B¹²C to ¹¹B¹²C model.     

Raman diagnostics of CVD systems: Determination of local temperatures

The suitability of local temperature measurements by cw Raman spectroscopy for the CH₄/H₂ CVD system has been established. The temperature profiles in a model reactor were derived from H₂ pure rotational lines and from hot bands of thev ₁ vibrational band of CH₄. Experimental results are presented for substrate temperatures of 773 K and of 1473 K. High accuracy of measurement and excellent agreement with theoretical solutions for the temperature field within the reactor were found.     

Diode-laser spectroscopy of supersonic free jets

A supersonic-free-jet infrared spectrometer has been constructed for investigation of molecular vibrational spectra at low rotational and vibrational temperatures. The sensitivity of measurement in a pulsed jet is increased by employing a phase-sensitive detection method synchronized with the pulse frequency. The performance of the spectrometer is examined for the absorption lines of the NH₃ v ₂ band. A rotational temperature as low as 16K is attained when seeded in He. Cold-jet spectra are demonstrated for thev ₃ bands of PF₅,³⁴SF₆, and¹⁸²WF₆.     

Vibrational modes of acid hydrogen in CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> and NaH<Subscript>5</Subscript>P<Subscript>2</Subscript>O<Subscript>6</Subscript>: inelastic neutron scattering

The vibrational modes of hydrogen bonds in CsH₅(PO₄)₂ and NaH₅P₂O₆ compounds are analyzed via inelastic incoherent neutron scattering in a wide range of temperatures and Raman light scattering at room temperature. The energy ranges have been determined for the γ, jg, and ? bands of the vibrational modes of acid hydrogens of these compounds. The dependences of the energy on the length of hydrogen bonds in CsH₅(PO₄)₂ have been revealed.     

Rotational and vibrational temperatures of electronically excited BiN radicals in a chemiluminescent flame

Rotational and vibrational temperatures of electronically excited BiN radicals in a low-pressure Bi_x+N/N₂*/N₂+Ar chemiluminescent flame have been deduced from high-resolution Fourier-transform emission spectra. Bands of three electronic transitions, a³Σ⁺(a₁1)→X¹Σ⁺(X0⁺), b⁵Σ⁺(b₁0⁺)→X¹Σ⁺(X0⁺), and b⁵Σ⁺(b₁0⁺)→a ³Σ⁺(a₁1), were analysed to determine the optical temperatures in the a³Σ⁺(a₁1) and b⁵Σ⁺(b₁0⁺) states. The rotational temperatures characterising the rotational populations in the a₁1, v=0 and 1 states were determined from the a₁→X, 0-2, 0-3, 0-4, 1-1, and 1-2 bands. The b₁→X, 0-8 and 0-11 bands, and the b₁→a₁, 0-0 bands served to determine the rotational temperature of the radicals in the b₁0⁺, v=0 state. The temperatures derived from the various bands and transitions were well consistent and the mean rotational temperature was determined to be 353±18 K, which is close to the translational temperature of the gas.Vibrational temperatures of the radicals in the a₁1 and b₁0⁺ states were derived from band intensities of the a₁→X and from the b₁→X as well as b₁→a₁ systems, respectively. The Franck-Condon factors needed were calculated with RKR potentials deduced from literature values of the rotational and vibrational constants in the three states involved. The a₁1 vibrational temperature (336±21 K) was close to the rotational temperature, while the b₁0⁺ vibrational temperature (438±36 K) differed, likely due to the previously observed perturbation of the b₁0⁺ state.     

High-Resolution Stimulated Raman Spectroscopy of Cl2, Cl2, and ClCl

A high-resolution rovibrational Raman spectrum of a sample of Cl₂ has been recorded at room temperature using a quasi-cw stimulated Raman technique. Three Q-branch structures belonging to the fundamental vibrations of the three chlorine isotopomers present in the sample in natural abundances and two weaker Q branches belonging to the first hot bands of the two more abundant isotopomers, ³⁵Cl₂ and ³⁵Cl³⁷Cl, have been observed. Lines with values of J up to 60 for the fundamentals and 50 for the hot bands have been measured in these fully resolved structures. Some additional lines belonging to O and S branches of the fundamentals and hot bands have also been recorded. The analysis of these data has rendered a new and more precise set of rotational molecular constants and band origins for the first three vibrational states of the chlorine isotopomers.     

Matrix isolation studies and potential function for perfluorocyclobutane

The infrared and Raman spectra of perfluorocyclobutane isolated in argon matrices at 1:100 and 1:200 mole ratios have been measured between 200 and 2000 cm^?1. Although the ring-puckering fundamental (ν₁₆) was not observed directly, an assignment for the 2 ← 1 (30 cm^?1) transition of ν₁₆ has been deduced from sum and difference bands resolved in the infrared spectrum. Potential functions based upon valence force models are considered in detail and correlated with those of similar ring systems. By using the frequency of the 2 ← 1 transition for ν₁₆ and a vibrational reduced mass of 1501 amu, an approximate model potential function calculation yields a slightly puckered equilibrium conformation with a barrier on the order of 124 cm^?1. The vibrational assignment for perfluorocyclobutane is discussed in terms of the new matrix isolation spectra.     

High temperature O2-CARS thermometry

O₂ temperature measurements at T=1910K have been performed by coherent anti-Stokes Raman scattering (CARS) inside a homogeneously heated gas volume of a tube furnace. The oxygen CARS spectrum can now be modeled accurately within the higher vibrational levels of the Q-branch manifold populated at flame temperatures using recently available spectroscopic data and collisional broadening coefficients.     

Spectroscopy of phonon and vibronic states of YbAl3(BO3)4 single crystal

The polarized Raman and reflection spectra of a single crystal YbAl₃(BO₃)₄ at room temperature were studied. Raman active vibrational modes A ₁, E _TO, and E _LO are identified. In the Raman spectrum, we detected an intense line at a frequency of 1018 cm⁻¹, which refers to internal vibrations of the BO₃ group and is known to be promising for use in amplifiers based on stimulated Raman scattering. From the simulation of reflection spectra by the method of dispersion analysis the frequencies of A ₂ vibrational modes were determined. Intense bands observed in the low-temperature transmission spectra in the range of f-f transitions in the Yb³⁺ ion are attributed to electron-phonon transitions. The Raman lines are compared with electron-phonon lines in the transmission spectrum.     

A non-equilibrium atmospheric pressure Capacitively-Coupled-Plasma (CCP) driven at VHF (162 MHz) for plasma catalysis of CO2 into CO

The design of a Very-High-Frequency (VHF) 162 MHz driven atmospheric-pressure Capacitively-Coupled-Plasma (CCP), with top and bottom electrodes operated in push-pull configuration, powered via a Power-Splitting-Transmission-Line-Driver (PSTLD), is presented. Application to the reprocessing of carbon dioxide into carbon-monoxide in this "high” VHF atmospheric plasma is presented, demonstrating some behaviour of the plasma source. rf power in the system is characterized using measured current (~ 1′s Amps peak) and voltage (~ 10′s Volts peak) waveforms at the electrode; Both are sinusoidal confirming a glow-discharge operational condition. Analysis of Optical Emission Spectra results find a highly non-equilibrium plasma, with high vibrational temperatures (from N₂) in the range ~4000 K, while gas temperature, monitored by a thermocouple at the gas outlet, remains low ~300 K, and confirmed by analysis of the N₂ rotational bands. The relative density of CO produced, as a by-product of CO₂ dissociation, is measured optically using N₂ as an actinometer. The CO density increases with rf power and longer gas residence times in the plasma volume. The high VHF atmospheric plasma is found to operate in pure CO₂ flows (no helium) with minimal gas heating for the full range of power densities (specific energy input of 0.4–2 eV per molecule) investigated.     

Theory of intercollisional interference effects: V. Pressure shift of the interference minimum in the Q branch of H2-rare gas mixtures

We extend our previous kinetic theory of intercollisional interference effects to include vibrational perturbations in collisions, and so obtain expressions for the pressure shifts of the interference minima in H₂-rare gas mixtures. These shifts are found to be different from those of the isotropic Raman Q lines in the same systems. The use of phase space averages for the analysis of Raman line shifting is discussed.     

Atypical intensity distribution in the Raman spectrum of 9,10-anthraquinone

The structure, the frequencies of the normal vibrations, and the absolute intensities of the bands in the IR and Raman spectra of 9,10-anthraquinone and its four symmetrical isotopomers are calculated in terms of the DFT/B3LYP method with the 6-31G(d) basis set. The effective harmonic force field of 9,10-anthraquinone is found by the Pulay method. A technique for directly obtaining the effective force fields without using experimental data on the frequencies of fundamental vibrations is proposed. An atypical intensity distribution in the Raman spectrum of 9,10-anthraquinone between two totally symmetric A _g and two nontotally symmetric B _3g vibrations is found. A new interpretation of these four experimentally observed vibrational Raman bands is proposed.     

Light scattering from soft modes in ferroelectric BaZnF4 and BaMgF4

Crystals of the BaM²⁺F₄ family are known to be ferroelectric with extra-polated Curie temperatures lying 100 K or less above their melting points. In the present Raman study the anomalous temperature dependences of frequency and intensity for one vibrational mode in BaZnF₄ and BaMgF₄ are correlated with dielectric properties.