电光效应的自相似性

通过对KNbO₃,LiNbO₃,BaTiO₃及几种半导体晶体的电光系数进行数值分析，发现电光系数在自由状态和受夹状态下对应的Miller-δ系数相同，与外加电场频率无关，进而提出用Miller-δ系数表征晶体非线性光学性质.在此基础上，提出一种全新的电光效应产生机制，认为电光效应源于非线性系统的自相似性，表现为对线性性质的一种“自我复制”，而Miller-δ系数是“自我复制”的比例因子. 关键词： 电光效应 非线性光学 自相似性     

Fluctuations and Landau-Devonshire expansion for barium titanate

The experimentally observed temperature dependence of the quartic coefficients in the Landau-Devonshire expansion for BaTiO₃ is naturally accounted for within a proper fluctuation model. It is explained, in particular, why one of the quartic coefficients varies with temperature above T _c , while the second is constant. It is argued that the tetragonal phase in BaTiO₃ exists essentially due to thermal fluctuations, while the true Landau-Devonshire expansion with temperature-independent coefficients favors the rhombohedral ferroelectric phase.     

晶体电光和非线性光学效应的离子基团理论(Ⅲ)——利用畸变氧八面体的离子基团模型计算LiNbO3,LiTaO3,KNbO3,BNN晶体的电光和倍频系数

本文用文献[1]中所提出的(MO₆)离子基团模型,计算LiNbO₃,LiTaO₃,KNbO₃,BNN等晶体的电光和倍频系数。假设在O_h对称时,这些晶体中的氧八面体具有相同的能级和对称波函数,则通过群表示理论就可得到在C_3ν,C_2ν对称性时氧八面体的能级和对称波函数,并进而用ABDP理论计算它们的电光和倍频系数。计算结果和实验符合得相当好。本文并从理论上解释了这些晶体的倍频系数大小、符号和氧八面体畸变间的关系,由此可以得到以下两个结论:(1)畸变氧八面体的离子基团模型不但适用于钙钛矿型材料,同时也适用于钨青铜型、LiNbO₃型材料。(2)在钨青铜型、LiNbO₃型的材料中,仍是“离子键”对电光和倍频效应作出主要贡献,同时由于LiTaO₃的共价键成份比LiNbO₃大,因而LiTaO₃的非线性光学效应比LiNbO₃小。     

Temperature dependence of linear electrooptic coefficients r 113 and r 333 in lithium niobate

A new method of determination of individual linear electrooptic coefficients is proposed. The technique is based on the dynamic polarimetric measurements and takes into consideration the temperature dependences of ordinary and extraordinary refractive indices. Results obtained for the electrooptic coefficients r₁₁₃ and r₃₃₃ in LiNbO₃ are presented. The coefficients are found to increase significantly within the considered temperature range 25-200°C. The temperature dependences of the intrinsic coefficients m₁₁₃ and m₃₃₃, defined in terms of the induced polarisation, are considered as well.     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.     

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF₆, CF₄, SiF₄, NF₃, CHF₃, CC1F₃, CBrF₃, OCS, N₂O, and CO₂ molecules in the liquid state and in solutions in liquefied Xe, Kr, and O₂ are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.     

光折变晶体Ce:BaTiO3电光和压电系数的测量

用干涉仪的方法测量了Ce:BaTiO₃晶体的低频电光系数和压电系数．排除压电效应对光通过晶体引起相位的变化，得到低频下经极化的Ce:BaTiO₃单晶的电光系数r₄₂=1945±220pm/V和r₁₃=11.8±1pm/V．从而，为研究Ce:BaTiO₃晶体的光折变效应和理论计算提供了精确的线性电光系数 关键词：     

Raman scattering,luminescence, and absorption edge under hydrostatic pressures of layered BiI3 and SbI3

Raman scattering from BiI₃ and SbI₃ crystals has been studied at hydrostatic pressures up to 2 GPa. The wavenumbers monotonically increased with pressure for all modes in BiI₃. Although both crystals belong to the same space group, the pressure coefficients of SbI₃ were significantly different from those of BiI₃. At pressure P₀ = 0.92 ± 0.01 GPa, the pressure coefficients of all modes changed. Above P₀, all modes in SbI₃ had positive pressure coefficients as they have in BiI₃. By comparing this unusual behavior of the Raman lines in SbI₃ around P₀ with the results in BiI₃ and comparing the two lattice structures, we suggest that the type of bonding of SbI₃ changes to become more ionic and hence more similar to the bonding of BiI₃. This change in structure is supported by changes in the bandwidth of the self‐trapped exciton (STE) luminescence and the slope of the absorption edge photon energy versus pressure. Copyright © 2007 John Wiley & Sons, Ltd.     

Measured and predicted band model parameters of BF3(v3) at high temperatures

Two experimental techniques were used to determine the high temperature infrared absorption coefficients of the v₃ band of BF₃. A high temperature flow tube fitted with a multipass infrared absorption cell was used to determine the BF₃ absorption coefficients at 295, 585, 870, 1150, and 1440K. BF₃ was also used in a flame emission-absorption apparatus to determine the BF₃ absorption coefficients at 2400 K.A generalized formulation for predicting the S/d and 1/d band model parameters of symmetric top perpendicular bands of MX₃ molecules is presented. The effect of including nuclear spin statistics in computing the S/d and 1/d band model parameters is considered. It is shown that nuclear spin statistic?s effect only the 1/d parameter and are significant only for the case of zero nuclear spin. A number of practical considerations, which arise in designing a computer algorithm to calculate the S/d and 1/d parameters, are discussed.Comparisons of the theoretical and experimental BF₃ absorption coefficients are made. Good agreement between theory and experiment at all temperatures was obtained by adjusting only two vibrational energy coupling constants, _χ23 and _χ34. Predicted S/d and 1/d band model parameters at 300, 600, 900, 1200, 1500, 2000, 2500, and 3000 K are presented.     

ABSORPTION INTENSITIES, PRESSURE-BROADENING AND LINE MIXING PARAMETERS OF SOME LINES OF NH3 IN THE ν4 BAND

The intensities and foreign gas broadening coefficients of 57 selected lines of the ν₄ band of NH₃ have been measured in the region of 1550 cm^-1 using a high resolution Brucker Fourier transform spectrometer. The line intensities were obtained by using the methods of absorbance at the line center and by fitting Voigt profiles to the measured shapes of the lines. The latter method also provides the collisional widths of the lines. In addition, collision cross relaxation coefficients of O₂ and air foreign gases were measured for 9 doublets of NH₃ in the ν₄ band. The J and K quantum numbers dependencies of pressure-broadening coefficients and line intensities are discussed. The observed air broadening and cross relaxation coefficients were found to be in reasonable quantitative agreement with the concentration-weighted average of the N₂ and O₂ broadening coefficients. The comparison of our present and previous results obtained for the NH₃–H₂, NH₃–air, NH₃–N₂ and NH₃–CO₂ collisions shows an increase of the pressure broadening and cross relaxation coefficients with quadrupole moment of the foreign gas. The analysis of the line intensities was based on the third-order theory of line strengths and yields effective transition moments, vibrational band strengths and correction parameters of the symmetric and antisymmetric partial bands of the fundamental ν₄ band.     

低温相偏硼酸钡(β-BaB2O4)晶体倍频系数的计算

本文从“离子基团理论”出发,并考虑A位离子晶格电场对(B₃O₆)^3-环的影响,采用CNDO/S近似计算了(B₃O₆)^3-基团的分子轨道,进而求得低温相偏硼酸钡(β-BaB₂O₄)晶体的倍频系数。计算结果与实验值符合,由此进一步证实了这一论点:β-BaB₂O₄晶体的倍频系数主要来自(B关键词：     

Coefficients of interest for molecular spectroscopy

Some basic considerations on the coupling coefficients for a chain of molecular groups starting from the natural universal covering SU₂ of the proper rotation group SO₃ are reviewed. Special emphasis is placed on the so-called f coefficients. Similar coefficients introduced by various people working in the field of molecular physics are related to the f and associated coefficients. The f coefficients are useful in different branches of molecular spectroscopy. Some specific applications to the ligand field theory are discussed in detail.     

Piezooptical effects in the tellurite glasses doped by europium and gold

We present the temperature dependence of piezooptical coefficients for three samples of TeO₂-GeO₂-PbO glasses doped with 0.5% of Eu₂O₃, 0.5% and 1% of Au₂O₃, after different thermoannealing times. We have established that there exist two temperatures singularities - minima in the range 655-695 K and maxima - at 850 K. It is crucial that for the glasses annealed during 61 h, at temperatures about 850 K, the anomaly of piezooptical coefficient disappears. Simultaneously the minima within the range 655-695 K changed depending on the duration of the thermoannealing which leads to low temperature shift of the minima. Towards lower temperature the piezooptical maxima occurs around 850 K and disappears after the increase of the annealing time. It is also crucial that the values of the piezooptical coefficients decrease with the enhancement of the thermoannealing. The observed temperature dependence with the piezooptical coefficients has a good correlation with the temperature dependences of the DSC. We have found that the pure glasses and glasses doped only by Au₂O₃ and Eu₂O₃ possess the piezooptical coefficients one order less with respect to the samples possessing simultaneously Au₂O₃ and Eu₂O₃.     

Growth mechanism of tantalum silicides by interdiffusion

Interdiffusion studies were conducted to understand the atomic mechanism of the diffusing species and the growth mechanism of the phases. Integrated diffusion coefficients and the ratio of tracer diffusion coefficients were estimated for these analyses. The activation energies for the integrated diffusion coefficients were calculated as 550?±?70 and 410?±?39?kJ/mol in the TaSi₂ and Ta₅Si₃ phases, respectively. In the TaSi₂ phase, Ta has a slightly lower but comparable diffusion rate with respect to Si, although no Ta–Ta bonds are present in the crystal. In the Ta₅Si₃ phase, Si has a higher diffusion rate, which is rather unusual, if we consider the atoms in the nearest-neighbour positions for both the elements. The ratio of Si to Ta tracer diffusion coefficients is found to be lower in the Si-rich phase, TaSi₂, compared to the Si-lean phase, Ta₅Si₃, which is also unusual. This indicates the type of structural defects present. An analysis on the growth mechanism of the phases indicates that duplex morphology and the Kirkendall marker plane should only be present in the TaSi₂ phase. This is not present in the Ta₅Si₃ phase due to the very high growth rate of the TaSi₂ phase, which consumes most of the Ta₅Si₃ phase layer. The problems in the calculation method used previously by others in this system are also explained.     

Calculation of the relaxation parameters of overlapping lines of the ammonia molecule pressure broadened by argon and helium

Broadening coefficients γ and interference coefficients ξ are calculated for different bands of the ammonia molecule in the case of line broadening by the pressure of argon and helium. A model intermolecular potential is used. It is shown that taking into account the interference effect changes the calculated values of γ, which suggests that the model potential parameters should be redetermined. The vibrational dependence of coefficients ξ is analyzed, and they are compared to coefficients ξ calculated for the same lines of the ammonia molecule pressure broadened by H₂, O₂, N₂, and NH₃.     

Measurement of the vibrational energy-transfer rates in mixtures of polyatomic molecules

The pressure coefficient of the vibrational deexcitation of methanol molecules caused by collisions with NH₃, CO₂, SF₆ molecules and He atoms is measured by infrared-far-infrared double-resonance spectroscopy. Large coefficients are measured for those buffer gases which increase the output power of far-infrared lasers. For other buffer gases such as NH₃ and CO₂ the measured coefficients are zero within the limits of experimental error. The relevance to measurements on the photoacoustic trace-gas analysis is discussed.     

Thermoelectric transport coefficients of n-doped CaTiO3, SrTiO3 and BaTiO3: A theoretical study

Boltzmann transport equations and density functional theory calculations were employed to calculate the thermoelectric transport coefficients of CaTiO₃, SrTiO₃ and BaTiO₃. It was found that BaTiO₃ has the largest Seebeck coefficient and power factor. Then the transport coefficients were analyzed using the ‘Tight Binding Model’. The band narrowing, caused by the increasing lattice constants from CaTiO₃ to BaTiO₃, was the main reason for the increasing Seebeck coefficients and the decreasing electrical conductivity. The calculated electrical conductivity and electronic thermal conductivity were in line with the Wiedemann-Franz law and the Lorenz factor was determined to be 2.45 for these oxides as degenerate semiconductors. Our theoretical results are helpful for seeking high performance thermoelectric oxides.     

Cation inter-diffusion between LaMnO3 and LaCoO3 materials

Cation inter-diffusion between polycrystalline LaMnO₃ and LaCoO₃ pellets has been studied at 1373-1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman-Matano method from Mn³⁺ to Co³⁺ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O₃ solid solution suggested. Cation diffusion coefficients in the end members LaMnO₃ and LaCoO₃ were estimated. Cation mobility in LaMnO₃ is higher than in LaCoO₃. It is suggested that higher cation diffusion in LaMnO₃ is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn⁴⁺). The results are compared to previous reports on cation diffusion in perovskite oxides.     

Microwave absorption coefficients of atmospheric pollutants and constituents

Calculations of the transition frequencies and absorption coefficients of microwave rotational transitions are given for a number of atmospheric pollutants and constituents. New measurements of the absorption coefficients are made in the vicinity of 70 GHz. The apparatus used in these measurements is briefly described. The calculated absorption coefficients are compared with these measurements and with existing measurements at other frequencies where available. Transitions with frequencies up to about 200 GHz are considered for the molecules and radicals SO₂, O₃, H₂O, NO₂, H₂S, H₂CO, NH₃, CO, OCS, N₂O, NO, OH, O₂, SO. Also discussed are criteria for the selection of appropriate transitions for the development of high sensitivity monitors to be used in air pollution and combustion research.     

Material tensor parameters of LiNbO3 relevant for electro- and elasto-optics

The complete set of self-consistent parameters of nominally undoped LiNbO₃ crystals of congruent composition that describe the electro-optic, piezoelectric, elasto-optic, elastic, and dielectric response has been determined by numerically evaluating available measurements. The parameters were determined at room temperature and consist of the low-frequency clamped dielectric constants ε^S _ij, elastic stiffness constants at constant electric field C^E _ijkl, piezoelectric stress coefficients e_ijk, elasto-optic constants at constant electric field p^E _ijkl, and clamped electro-optic coefficients r^S _ijk. It is shown that the complete set is required for calculating the effective electro-optic coefficients and dielectric constants in photorefractive applications of LiNbO₃. Received: 4 January 2002 / Revised version: 1 February 2002 / Published online: 14 March 2002