掺Fe和掺Cr的LiNbO3单晶的全部弹性和压电参数的布里渊散射测量

本文测量了抛光球形单晶样品某一晶面内的布里渊散射。从得到的声速各向异性求出Fe:LiNbO₃和Cr:LiNbO₃晶体的全部弹性和压电参数,同纯LiNbO₃进行了比较,讨论指出:若干弹性张量组元的正、负号不确定是由坐标系的选择造成的。 关键词：     

理论研究B2分子X3Σg-和A3Πu态的光谱性质

采用Davidson修正的内收缩多参考组态相互作用方法及Dunning等的相关一致基aug-cc-pV6Z计算了B₂分子X³∑_g^-和A³Π_u电子态的势能曲线.利用总能量外推公式,将两个电子态的总能量分别外推至完全基组极限.对势能曲线进行核价相关修正及相对论修正计算,得到了同时考虑两种效应修正的外推势能曲线.通过同位素质量识别,得到了主要的同位素分子¹¹B¹¹B和¹⁰B¹¹B的X³Σ_g^-和A³Ⅱ_u电子态的光谱常数T_e,R_e,ω_e,ω_ex_e,ω_ey_e,B_e,β_e和γ_e.求解双原子分子核运动的径向Schr（o|¨）dinger方程,找到了无转动的同位素分子¹¹B₂（X³Σ_g^-,A³Π_u）和¹⁰B¹¹B（X³∑_g^-,A³Π_u）的全部振动态.针对每一同位素分子的每一振动态,分别计算了其振动能级和惯性转动常数等分子常数,它们均与已有的实验结果较为一致.其中,¹⁰B¹¹B（A^Π_u）分子的光谱常数和分子常数属首次报道.     

OH-吸收带作为铌酸锂晶体缺陷结构的探针

本文报道了一组不同Li/Nb比和另一组不同掺Mg浓度的LiNbO₃晶体室温OH^-吸收带的实验结果,观察到OH^-吸收带的三峰结构及其随Li/Nb比的变化,以及重掺Mg晶体中(6mol％MgO)OH^-吸收带转变为双峰结构,并向高能端移动54cm^-1。根据LiNbO₃的晶体结构以及Abrahams和Smyth的缺陷结构模型,对化学计量晶体、一致熔化晶体和掺Mg晶体分别进行讨论。并提出重掺Mg晶体中OH^-吸收带向高能端的移动可能是由于当掺Mg浓度超过阈值后Mg²⁺离子开始进入Nb位而引起的。 关键词：     

利用Townsend放电测定N2(A3∑u+)亚稳态分子的扩散系数和猝灭速率常数

在纯N₂气体中,利用Townsend放电方法,对N₂(A³∑_u⁺)亚稳态分子的扩散系数D_m和猝灭速率常数K_q的测定进行了研究。分别得到:D_m=128cm²/s,K_q=8.1×10^-19cm³/s。 关键词：     

SrNb2O6-NaNbO3-LiNbO3赝三元系相图的研究

本文用X射线衍射、热处理及差热分析等方法测定了SrNb₂O₆-NaNbO₃-LiNbO₃赝三元系的室温截面及相应的SrNb₂O₆-NaNbO₃,SrNb₂O₆-LiNbO₃和NaNbO₃-LiNbO₃等三个赝二元系相图;粗略地研究了Sr_0.42Na_0.16NbO₃-LiNbO₃系的纵截面;含5mol％LiNbO₃及10mol％LiNbO₃的SrNb₂O₆-NaNbO₃的纵截面。确定了室温Sr₂Na(NbO₃)₅(以下略为S₂N)相为四方钨青铜结构。其点阵常数为a=12.36?,c=3.906?.LiNbO₃在S₂N相内的溶解度可达～10mol％,当LiNbO₃含量超过5mol％时,S₂N相畸变为S₂N′相。S₂N′相为正交晶系。实验确定室温S₂N(S₂N′)相系亚稳相。在900-1100℃长时间退火即分解为SrNb₂O₆和以NaNbO₃为基的固溶体的混合物。 关键词：     

Eu3+掺杂的铌酸钠钾陶瓷的制备及性能研究

采用固相烧结法制备了Eu³⁺掺杂的铌酸钠钾（KNN）陶瓷。用X射线粉末衍射仪、荧光光谱测试仪和LCR精确阻抗测试仪等对其结构、发光性能和介电性能进行表征。XRD结果显示样品为钙钛矿结构。荧光分析结果表明,致密度对KNN陶瓷材料发光性能有一定的影响,Eu³⁺掺杂量是影响其发光性能的重要因素。其中掺杂Eu摩尔分数为4%的样品在930℃焙烧后其发光最强,在396 nm紫外光激发下,发射光谱最强峰在614 nm,对应于Eu³⁺的⁵D₀-⁷F₂电偶极跃迁。样品经3 kV/cm、110℃极化30 min后进行压电性能检测,结果表明提高Eu³⁺掺杂量以及陶瓷的致密度,可改善压电性能。其中掺杂4%Eu的KNN压电常数D₃₃最大为98 pC/N,在1 kHz、100℃时,介电常数最小为217,介电损耗tanθ=0.199,且仍然保持较高的居里温度T_c=426℃。     

S2分子B″3Πu态的势能函数和光谱常数的理论研究

推导了S₂分子B″³Π_u态的合理离解极限.用Gaussian 94 QCISD(T)方法和6-311++G^**基组计算了S₂分子B″³Π_u以及X³Σ^-_g态的势能曲线.给出了S₂分子B″³Π_u态的Murrell-Sorbie势能函数和光谱常数.B″³Π_u与B³Σ^-_u态在排斥支重叠范围大；同时，B″³Π_u与X³Σ^-_g态有相同离解极限，因而，在吸引支有重叠.讨论了B″³Π_u与B³Σ^-_u和X³Σ^-_g态相互作用的特征. 关键词：     

75As32S+和75As34S+离子的光谱常数与分子常数

采用内收缩多参考组态相互作用(MRCI)方法, 结合Dunning系列相关一致基, 分别对⁷⁵As³²S⁺和⁷⁵As³⁴S⁺离子的X³Σ^-和A¹Π电子态的势能曲线进行了计算, 进一步拟合势能曲线, 得到各电子态的光谱常数与分子常数. 首先, 采用MRCI方法结合相关一致基, aug-cc-pV5Z, 对AsS⁺离子的X³Σ^-和A¹Π 电子态进行了计算, 获得相应的势能曲线; 然后, 为进一步提高势能曲线的精度, 对其进行了三种修正计算. 采用Davidson(+Q)方法修正MRCI 方法计算过程中存在的基组大小不一致缺陷; 利用二阶Douglas-Kroll哈密顿近似, 在cc-pVQZ基组水平, 修正了相对论效应对势能曲线的影响; 利用两点能量外推法, 在aug-cc-pVQZ和aug-cc-pV5Z基组水平对各能量点的势能值进行了外推, 得到完全基组极限处的势能曲线. 最后, 利用修正(包括Davidson修正、相对论修正和基组外推)后的势能曲线, 通过Vibrot程序, 求解双原子分子核运动的径向Schrödinger方程, 并进行同位素质量识别, 得到⁷⁵As³²S⁺和⁷⁵As³⁴S⁺离子两个电子态的光谱常数(T_e, R_e, ω_e, ω_ex_e, α_e 和B_e)和分子常数(G(ϒ), B_v, D_v).     

不同组分的LiNbO3晶体的吸收边研究

本文通过对不同组分LiNbO₃晶体的α^1/2-hν曲线的研究,肯定了3.8eV以下的吸收边的间接跃迁性质,并给出了三段直线的合理归属。根据LiNbO₃的晶格常数随组分变化的情况,提出了能带结构随组分变化的设想,它解释了我们和Redfield等人有关吸收边的实验结果。 关键词：     

高温条件下Ga3PO7晶体热学及声表面波性质的理论研究

高温压电晶体是许多机电器件必需的一种多功能材料, Ga₃PO₇晶体的居里温度高达1364 ℃, 可应用于高温极限条件. 但是预测高温极限条件下晶体的结构以及物理性质的问题采用实验研究的手段非常困难, 而理论上的预测未见研究. 本文采用密度泛函-准谐振近似理论计算了温度在0-1200 ℃范围内Ga₃PO₇ 晶体的结构常数和热学性质, 结果表明Ga₃PO₇晶体的晶格常数a和c随温度的升高呈线性增大, 且c方向受温度影响更为显著; 晶体的密度随温度的升高而减小, 计算的a 和c方向平均热膨胀系数分别为1.67×10^-6 K^-1和3.58×10^-6 K^-1, 高温区定压热容为2.067 J/g·K, 与实验值一致. 计算了从常温到高温下该晶体的弹性常数以及体弹性模量的变化, 研究了高温条件下的声表面波特性, 发现随着温度的升高, 声表面波速度浮动较小, 而机电耦合系数略有增大; 在传播角为151° 时该晶体具有较好的温度稳定性且机电耦合系数达到最大值, 这表明Ga₃PO₇ 晶体是一种有望应用于高温环境下的压电晶体.     

Low-temperature elastic constants and piezoelectric coefficients of langasite (La3Ga5SiO14)

A complete set of elastic constants C _ij and piezoelectric coefficients e _ij of a La₃Ga₅SiO₁₄ (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C _ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C ₄₄ and C ₁₄); (ii) monotonic elastic softening (C ₆₆); and (iii) a stiffening-to-softening transition below 150?K (C ₁₁, C ₁₂, C ₁₃ and C ₃₃). In addition, a strong correlation between C ₆₆ and the piezoelectric coefficient e ₁₁ was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A ₁ and doubly degenerated E symmetries in the point group D ₃.     

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     

Elastic constants of galena down to liquid helium temperatures

The elastic constants of single crystal galena have been determined from the measured ultrasonic velocities down to liquid helium temperature. A cryostat incorporating an arrangement to inject the liquid bonding material at low temperature is described. At 5 K, the values of elastic constants are C₁₁=14.9₀, C₁₂=3.5₁ and C₄₄=2.9₂×10¹⁰ N/m².     

Stiffness matrix and debye temperature of ReO3 from ultrasonic measurements

We have measured the propagation velocities of bulk acoustic waves in the simple cubic transition-metal oxide ReO₃ by ultrasonic pulse propagation. The elastic stiffness constants at 300 K are: C₁₁ = (47.9 ± 1.4) × 10¹¹ dyne/cm²; C₄₄ = (6.1 ± 0.2) × 10¹¹ dyne/cm²; C₁₂ = (?0.7 ± 2.8) × 10¹¹ dyne/cm². These elastic constants indicate a crystal with highly anisotropic shear propagation. The Debye temperature of the compound from these measurements is 528 K. This value is somewhat higher than previous results from specific heat and resistivity determinations.     

Elastic constants of sodium chlorate from 77 K to 350 K

The elastic constantsC ₁₁,C ₁₂ andC ₄₄ of sodium chlorate single crystal have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC ₁₁=4.90,C ₁₂=1.39,C ₄₄=1.17 (× 10¹⁰ N/m ²) at 298 K and 6.15, 2.16, 1.32 (×10¹⁰ N/m ²) at 77 K. The data agree well with the values measured earlier up to 223 K. Brief mention is also made of the low temperature bonding problems in these soft crystals.     

A note on the elastic constants of sodium bromate from 350 K to 77 K

The elastic constantsC ₁₁,C ₁₂ andC ₄₄ of sodium bromate single crystals have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC ₁₁=5.57₈,C ₁₂=1.07₅,C ₄₄=1.51₀ (×10¹⁰ N/m²) at 290 K and 6.35, 1.98 and 1.65 (×10¹⁰ N/m²) at 77 K. The present room temperature values agree closely with the recent values of Gluyaset al. but the other earlier measurements show some scatter. A comparison between the elastic constants of sodium bromate and sodium chlorate is also made.     

Anharmonic force constants of GaSb from the measured third order elastic constants at 300°K

The third-order elastic constants of single crystal GaSb are determined using ultrasonic pulse interferometer at 10 MHz. The constants at 300°K, in units of 10¹¹ N.m.⁻², are C_l11 = ™ 4 ·75 ± 0·06 C₁₄₄ = + 0·50 ± 0·25 C₁₁₃ = ™ 3 ·08 ± 0·02 C₁₆₆ = ™ 2·16 ± 0·13 C₁₂₃ = ™ 0 ·44 ± 0·29 C₄₅₆ = ™ 0·25 ± 0·15 These constants are used to evaluate the three anharmonic first and second neighbour force constants based on modified Keating’s model. The constants are (in units of 10¹¹ N.m⁻²)γ=− 2·406;δ=0·407;ε=−0·222.     

The elastic constants for single-crystal bismuth and tin from room temperature to the melting point

The six adiabatic elastic stiffness constants of bismuth and tin have been determined over a range of temperatures extending from room temperature to the melting point. These constants were computed from measurements of the ultrasonic wave velocity in high-purity, single crystal specimens. The constants for bismuth at the melting point are C₁₁ = 56·l C₁₃ = 24·2 C₁₄ = 60 C₃₃ = 34·9 C₄₄ = 90 C₆₆= 16·1 in units of 10¹⁰ dynes/cm². The constants for tin at the melting point (in the same units) are C₁₁ = 61·3 C₁₂ = 38·5 C₁₃ = 38·0 C₃₃ = 75·6 C₄₄ = 16·9 C₆₆ = 19·0.     

碘酸锂晶体全部电弹常数的测量

本文探讨了碘酸锂晶体(α-LiIO₃,简称LI)全部电弹常数的测试方法。以压电板厚度振动模理论,推导出LI晶体独立电弹常数计算公式。对无压电耦合的弹性常数C₁₁^E和C₆₆^E,采用了声光同步测速法进行测量。最后,测量给出了LI晶体全部电弹常数和一些机电耦合系数共52个数据。     

NH4IO3晶体的压电性能

用干涉法测量了NH₄IO₃晶体的全部压电系数。结果为: d₃₁=35.2, d₃₂=23.4, d₃₃=55.9, d₂₄=-2.4, d₁₅=-9.5×10^-8 CGSE/DYN。 关键词：