0.67 PbMg1/3Nb2/3O3-0.33 PbTiO3单晶中软模模式指认

应用显微拉曼技术对弛豫型铁电体0.67PbMg1/3Nb2/3O3-0.33PbTiO3(0.67PMN-0.33PT)的偏振拉曼光谱随温度变化的研究表明,在-196到600°C温度范围内0.67PMN-0.33PT存在两次相变:三方到四方(R-T)相变和四方到立方(T-C)相变。R-T相变的特征是106cm-1软模(-196°C时)随温度的升高而湮没到80cm-1"静态"模式中。依照群论分析,0.67PMN-0.33PT的80cm-1和106cm-1(-196℃时)两个模式分别为E(1TO)和A1(1TO)模。文章对三方相的对称结构(C3v点群)在背向散射配置下不同偏振方向的拉曼散射效率进行了计算。计算结果表明晶体中的A1(1TO)和E(1TO)模式能够通过使用不同的散射配置进行识别。理论计算和实验结果相比较得到了很好的吻合。     

弛豫型铁电单晶0.67Pb(Mg_(1/3)Nb_(2/3))O_3-0.33PbTiO_3的拉曼散射研究

本文采用拉曼散射技术在温度从374到-196℃的范围内,研究了弛豫型铁电单晶0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMNT)。观察了在不同温度下拉曼光谱的变化,经分析这些变化反映了该晶体经历了两个相变:第一个相变温度发生在120℃,从顺电立方相到铁电四方相的相变,780 cm-1处模式在VH偏振下的改变标志了这一相变;第二个相变温度发生在34℃,是从铁电四方相到铁电三方相的相变,软模的出现代表了这一相变。     

A polarized micro-Raman study of a 0.65PbMg1/3Nb2/303-0.35PbTi03 single crystal

Polarized micro-Raman spectra of a 0.65PbMg_1/3Nb_2/3O₃-0.35PbTiO₃ （0.65PMN-0.35PT） single crystal poled in the [001] direction are obtained in a wide frequency range （50-2000 cm 1） at different temperatures.The best fit to the Raman spectrum at 77 K is achieved using 17 Lorenzians to convolute into it,and this is proved to be a reasonable fit.According to the group theory and selection rules of overtone and combinational modes,apart from the seven Raman modes that are from first-order Raman scattering,the remaining ones are attributed to being from second-order Raman scattering.A comparison between the experimental results and theoretical predictions shows that they are in satisfactory agreement with each other.Our results indicate that at 77 K the sample belongs to the rhombohedral symmetry with the C 5 3v （R3m） space group （Z=1）.In our study,on heating,the 0.65PMN-0.35PT single crystal undergoes a rhombohedral → tetragonal → cubic phase transition sequence.The two phase transitions occur at 340 and 440 K,which correspond to the disappearance of the soft mode near 106 cm 1 recorded in VV polarization and the vanishing of the band around 780 cm 1 in VH polarization,respectively.     

Al‐for‐Fe substitution in hematite: the effect of low Al concentrations in the Raman spectrum of Fe2O3

Five different mixed Al‐hematites with an aluminium molar content varying from 0 to 10% were investigated by micro‐Raman spectroscopy to study the effect of Al‐for‐Fe substitution on the hematite lattice. A red shift of hematite vibrational wavenumbers and a line broadening were observed; also a shoulder located near 430 cm⁻¹ and a broad band at 670 cm⁻¹ developed. The variation of the spectral features is discussed in terms of a local disorder correlated to the insertion of Al³⁺ ions into the Fe(O)₆ octahedra constituting hematite structure. A multivariate analysis was also carried out on the spectral data to distinguish between the doped samples analysed. Copyright © 2007 John Wiley & Sons, Ltd.     

Ferroelectric Q and antiferroelectric P phases' coexistence and local phase transitions in oxygen‐deficient NaNbO3 single crystal: micro‐Raman,dielectric and dilatometric studies

Micro‐Raman studies of oxygen‐deficient gray‐colored NaNbO₃ single crystals have shown that at room temperature both antiferroelectric P and ferroelectric Q phases are present simultaneously as separate regions tens of micrometers in size. Phase transitions in P and Q regions have been elucidated by dielectric, dilatometric and micro‐Raman studies. For the first time, the sequence of phase transitions between antiferroelectric phase P and ferroelectric Q and N phases has been revealed. Copyright © 2012 John Wiley & Sons, Ltd.     

Disorder‐induced symmetry lowering in Ba(Y1/2Nb1/2)O3 ceramics probed by Raman spectroscopy

This work investigates the evolution of the crystal structure of microwave‐hydrothermal synthesized Ba(Y_1/2Nb_1/2)O₃ powders as a function of firing temperature by Raman spectroscopy. The samples were produced at 200 °C and fired at temperatures ranging from 600 to 1600 °C. Raman spectra were obtained at room temperature for all samples and the results showed that materials fired at 1600 °C exhibited tetragonal (I4/m or ) structure, whereas those fired at lower temperatures exhibited the triclinic (P1 or C_i¹) structure. The results were compared with those observed for ceramics obtained by conventional solid‐state methods. It is believed that the lowering of the symmetry verified in materials fired below 1600 °C is a consequence of the local disorder of Y⁺³ and Nb⁺⁵ ions in octahedral sites. Copyright © 2008 John Wiley & Sons, Ltd.     

Polarized Raman scattering in helimagnetic β‐MnO2

A rutile β‐MnO₂ film was grown on MgO substrate using plasma‐assisted molecular beam epitaxy (PAMBE) monitored by reflection high‐energy electron diffraction (RHEED). Polarized Raman spectra at various temperatures were obtained to investigate the influence of the helimagnetic structure on the vibrational modes of β‐MnO₂. A red shift of E_g modes indicates a gradual formation of spin angles between neighboring Mn⁴⁺ ions. The intensities of the E_g and A_1g modes with y‐polarized incidence increase remarkably below the Néel temperature. A new view as vibrational mode projection (VMP) indicates the interactions between the magnetic component of incident light and the helimagnetic structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Polarized Raman spectra of brushite (CaHPO4.2H2O) crystal. Investigation of the phosphate stretching modes,study of the LOTO splitting

Polarized Raman measurements were recorded on a monoclinic brushite (CaHPO₄.2H₂O) crystal in the 800–1200 cm⁻¹ spectral range, corresponding to the P O stretching modes. This study is a continuation of the investigation of the phosphate stretching modes observed in polarized infrared reflectance spectra of brushite crystal. In such ionic non‐centrosymmetric crystals, the splitting between the transverse and longitudinal components of the optic vibrations was observed in the polarized Raman spectra recorded at several scattering geometries. A″ symmetry modes of the brushite crystal were measured. Using a simple model based on the symmetry of the PO₄ group, the Raman intensities of the stretching modes are calculated and compared with experimental bands. Copyright © 2016 John Wiley & Sons, Ltd.     

New evidences of in situ laser irradiation effects on γ‐Fe2O3 nanoparticles: a Raman spectroscopic study

The nature of the physical mechanisms responsible for the structural modification of the γ‐Fe₂O₃ nanoparticles under laser irradiation has been investigated by Raman spectroscopy. In situ micro‐Raman measurements were carried out on as‐prepared γ‐Fe₂O₃ nanoparticles about 4 nm in size as a function of laser power and on annealed γ‐Fe₂O₃ particles. A baseline profile analysis clearly evidenced that the phase transition from maghemite into hematite is caused by local heating due to laser irradiation with an increase of grain size of nanoparticles. This increasing was clearly determined by X‐ray diffraction from 4 nm in nanoparticles up to more than 177 nm beyond 900 °C in a polycrystalline state. Copyright © 2010 John Wiley & Sons, Ltd.     

Micro‐Raman study of orbiton–phonon coupling in YbVO3

First‐order and multiphonon Raman active excitations are studied in YbVO₃ as a function of temperature in the orthorhombic and monoclinic phases. Below T ≃ 170 K, a G‐type orbital ordering with a concomitant monoclinic transition occurs. They enhance the phonon polarizabilities, allowing the resolution of room‐temperature bands, and activate new excitations around 700 cm⁻¹. Below T ∼ 65 K, the 700 cm⁻¹ excitations disappear, indicating a C‐type orbital ordering and a return to the orthorhombic structure. The observed phonon combinations around 1400 cm⁻¹ with a dominant Jahn‐Teller vibration at ∼690 cm⁻¹ reflect a possible orbiton‐phonon coupling. Copyright © 2011 John Wiley & Sons, Ltd.     

Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In_1/2Nb_1/2)O₃-35PbMg_1/3Nb_2/3O₃-32PbTiO₃ existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.     

Nanomechanics of single keratin fibres: A Raman study of the α‐helix →β‐sheet transition and the effect of water

The use of micro‐Raman spectroscopy, through chemical‐bond, nano‐scale probes, allows the changes in conformations (α‐helix →β‐sheet), chain orientation, breakage of disulfide bonds (20%) and the increase of intra‐ and inter‐chain distances during the application of stress to be distinguished. The combination of micro‐Raman spectroscopy and a Universal Fibre Tester allows a quantitative measurement of the extension of chemical bonds in the peptide chain during loading. The nano‐structural transformations of keratin during strain of human hair in a dry environment (40–60% relative humidity) and saturated with water have been studied. Water permits the sliding of the chains and decreases the bond energy of the hair. Spectral analyses and 2D correlation are two coherent and independent methods to follow the structural nano‐mechanical (Raman) and micro‐mechanical (strain/stress) analyses, and confirm the validity of the experimental results, tools and principles used, as well as the agreement with the structural model of keratin fibres described by Chapman and Hearle. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopic study of phase transitions in undoped morphotropic PbZr1−xTixO3

Several PbZr_1−xTi_xO₃ (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15–800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long‐range or short‐range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral–monoclinic–tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high‐T and low‐T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low‐T and high‐T Raman scattering spectra were collected on undoped PbZr_1−xTi_xO₃ with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long‐range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low‐T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Bi2ZnOB2O6单晶偏振拉曼光谱

本文通过分析不同几何配置下的偏振拉曼光谱对非线性光学晶体的晶格振动模式进行了研究. 首先根据因子群分析,将晶体的振动模按晶体对称群的不可约表示进行分类,其次测量了晶体在10–1600 cm^-1范围内,不同几何配置下的偏振拉曼光谱,并在此基础上指认了晶体的晶格振动模式. 300 cm^-1以下的振动峰,归结为晶体的外振动,来自[BiO₆],[ZnO₄],[BO₄]和[BO₃]原子基团的平动和转动;300cm^-1以上为晶体的内振动,主要与Bi-O,和Zn-O键振动有关. 晶体拉曼光谱中最高振动频率达到1407 cm^-1,被指认为[BO₃]三角形中B-O键的伸缩振动,体现了[BO₃]基团中高的电子非局域化程度. 关键词： 2ZnOB₂O₆单晶')" href="#">Bi₂ZnOB₂O₆单晶 偏振拉曼光谱 振动模式     

In vivo study on the protection of indole‐3‐carbinol (I3C) against the mouse acute alcoholic liver injury by micro‐Raman spectroscopy

Micro‐Raman spectroscopy (MRS) was utilized for the first time to evaluate the effect of indole‐3‐carbinol (I3C) on acute alcoholic liver injury in vivo. In situ Raman analysis of tissue sections provided distinct spectra that can be used to distinguish alcoholic liver injury as well as ethanol‐induced liver fibrosis from the normal state. Sixteen mice with liver diseases including acute liver injury and chronic liver fibrosis, and eight mice with normal liver tissues, and eight remedial mice were studied employing the Raman spectroscopic technique in conjunction with biomedical assays. The biochemical changes in mouse liver tissue when liver injury/fibrosis occurs such as the loss of reduced glutathione (GSH), and the increase of collagen (α‐helix protein) were observed by MRS. The intensity ratio of two Raman peaks (I₁₄₅₀/I₆₆₆) and in combination with statistical analysis of the entire Raman spectrum was found capable of classifying liver tissues with different pathological features. Raman spectroscopy therefore is an important candidate for a nondestructive in vivo screening of the effect of drug treatment on liver disease, which potentially decreases the time‐consuming clinical trials. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1, 2ν1–ν1, ν2, 2ν2, and 3ν2–ν2 bands of CF4

The spectra of the ν₁, 2ν₁–ν₁, ν₂, 2ν₂, and 3ν₂–ν₂ bands of CF₄ were obtained with a quasi‐continuous wave stimulated Raman spectrometer. These five bands were studied at a temperature of 135 and 300 K (for the hot bands). The spectrum of ν₁ was obtained at a sample pressure of 2 mbar. For the spectra of the other regions, which are much weaker, higher pressures were used. The analysis has been performed thanks to the xtds and spview softwares developed in Dijon for such highly symmetric molecules. Combining the present results with a previous infrared study, we could determine a very accurate value for the C–F equilibrium bond length, i.e. r_e = 1.31588(6) Å. Copyright © 2013 John Wiley & Sons, Ltd.     

Piezoelectric properties of PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics

(1 – x)Pb(Hf_1–yTi_y)O₃–x Pb(Mg_1/3Nb_2/3)O₃ (x = 0.1 ～ 0.25, y = 0.555) ternary piezoelectric ceramics were prepared using the two‐step precursor method. Morphotropic phase boundary (MPB) compositions, located at x = 0.18 ～ 0.22, were confirmed using X‐ray diffraction and by their dielectric, piezoelectric and ferroelectric properties. The optimum dielectric and piezoelectric properties were achieved for the MPB composition 0.8Pb(Hf_0.445Ti_0.555)O₃–0.2Pb(Mg_1/3Nb_2/3)O₃, with dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p and Curie temperature T_C being on the order of 2800, 680 pC/N, 70% and 276 °C, respectively. Of particular significance is that the new ternary ceramics exhibit comparable piezoelectric and electromechanical properties to commercial PZT5H ceramics, but with much improved T_C, showing a potential for applications at elevated temperature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)