使用基团理论计算KB5O8·4H2O晶体的倍频系数

本文使用基团理论计算KB₅O₈·4HO₂O(简称KB5)晶体的倍频系数,得到d₃₁=2.61×10^-10esu,d₃₂=007×10^-10esu,d₃₃=3.26×10^-10esu,与实验值符合较好。计算结果表明:氢键对KB5晶体的倍频系数有影响。本文还分析了KB5晶体倍频系数小的起因,除去[B₅O₆(OH)₄]^-1基团的微观倍频系数小外,还在于基团的空间排列方式不利,导至最大的微观倍频系数X₁₂₃相互抵消。最后,本文提出了在含四配位硼原子的硼氧化合物中寻找倍频新材料的结构判据。 关键词：     

NaNO2晶体线性和非线性光学系数的计算

使用从头计算平面波赝势方法,计算了NaNO₂晶体电子能带结构,并使用改进的倍频公式计算了它的线性折射率和静态二级非线性系数,所得到的结果和实验值相符.采用实空间原子切割方法分析了阳离子和阴离子基团对光学性质的贡献.计算表明(NO₂)-基团对双折射率和倍频系数的贡献占主要地位,从而进一步验证了阴离子基团理论的正确性 关键词： 电子结构 非线性光学系数 从头计算方法     

使用CNDO/S型近似方法计算NaNO2晶体的倍频系数

本文使用CNDO/S型近似方法,计算(NO₂)^-1的单电子分子轨道,然后按基团理论的通用计算程序计算NaNO₂晶体的倍频系数,计算值和实验值符合得较好,计算结果明确指出:NaNO₂晶体倍频系数各向异性的原因来自基团的共轭π轨道,另外,本文的计算表明,有可能对非线性光学新材料探索提供计算机的预测。本文还就非线性光学效应的双能级模型作了讨论,并指出了它的局限性。 关键词：     

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：     

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：     

使用基团理论计算KB_5O_8·4H_2O晶体的倍频系数

本文使用基团理论计算KB_5O_8·4HO_2O(简称KB5)晶体的倍频系数,得到d_(31)=2.61×10~(-10)esu,d_(32)=007×10~(-10)esu,d_(33)=3.26×10~(-10)esu,与实验值符合较好。计算结果表明:氢键对KB5晶体的倍频系数有影响。本文还分析了KB5晶体倍频系数小的起因,除去[B_5O_6(OH)_4]~(-1)基团的微观倍频系数小外,还在于基团的空间排列方式不利,导至最大的微观倍频系数X_(123)相互抵消。最后,本文提出了在含四配位硼原子的硼氧化合物中寻找倍频新材料的结构判据。     

Na2O-Al2O3-P2O5系统玻璃中的[Al-O-P]-基团

本文报道Na₂O-Al₂O₃-P₇O₅系统玻璃中[Al-O-P]^-基团的Raman谱。我们把高频峰有规律地移向低波数归结为由[Al-O-P]^-基团构成的玻璃网络聚合度下降造成。 关键词：     

使用等价轨道法计算AB型晶体的倍频系数

在忽略电子-声子相互作用的基础上,本文探讨了从能带波函数出发计算AB型晶体倍频系数的可能性。采用计算AB型晶体能带的近似方法——等价轨道法。计算了k=0点的倍频系数,然后通过带宽的修正,使k=0点的倍频系数近似地表为不同k点倍频系数的平均,这一平均值乘以第一布里渊区内k点的总数就是晶体的宏观倍频系数。计算了十七种闪锌矿型和纤维锌矿型晶体的倍频系数,计算值和实验值的吻合相当满意。从中得出几点有用的结论:(1)倍频系数的双能级跃迁模型对闪锌矿型结构是适用的;但对纤维锌矿型结构并不适用。(2)纤维锌矿型晶体的X₃₃₃^2ω系数可表示成两项之和:单重态(Γ₁,Γ₃)的贡献和双重态(Γ₅,Γ₆)的贡献。其中单重态对倍频系数贡献正值,双重态贡献负值。(3)使用Pauling的离子性标度f_i来表征A—B键的离子性是适宜的。 关键词：     

铁电晶体PbxBa1-xNb2O6和掺Li,Na的PbxBa1-xNb2O6的结构和电弹张量的测定

用提拉法从熔体中生长出Pb_0.37Ba_0.63Nb₂O₆和Pb_0.30Ba_0.533Na_0.306Li_0.028Nb₂O₆两种铁电单晶。用X射线衍射方法分析了两种单晶的结构,结果表明,室温时两种晶体都属于四方晶系点群4mm。测定晶格参数得PBN晶体的a=12.493?和c=3.98?;掺Li,Na的PBN晶体的a=12.493?和c=3.970?。测定了两种晶体全部各52个电弹张量的分量,结果表明PBN晶体具有优良的压电性,其中压电系数d₁₅=108×10^-12C/N。这种晶体很有希望用作与厚度切变模式有关的压电换能器材料。掺Li,Na的PBN晶体的介电常数显著降低,而铁电居里点有明显的提高。 关键词：     

晶体电光和非线性光学效应的离子基团理论(Ⅱ)——利用(IO3)-1离子基团的分子轨道计算α-LiIO3晶体的倍频系数

本文对碘酸盐晶体的倍频效应提出了一个(IO₃)^-1离子基团模型,并用(IO₃)^-1离子基团的分子轨道计算了α-LiIO₃的倍频系数,计算值和实验值符合得很好。由此得出以下结论:碘酸盐晶体的倍频效应主要由(IO₃)^-1离子基团和它的共价键轨道所决定。而在(IO₃)^-1离子基团中,对倍频效应作出主要贡献的是碘的孤对电子轨道和氧的|2σ>,|2P_y>轨道。     

Growth, microhardness, dielectric and photoconductivity characterization of a highly polarizable NLO material: Sodium p-nitrophenolate dihydrate (NO2-C6H4-ONa.2H2O)

Sodium p-nitrophenolate dihydrate (NPNa.2H₂O) is a highly polarisable non linear optical material. It has a d_eff about 1.45 times than that of potassium titanyl phosphate. Single crystals of (NPNa.2H₂O) have been grown successfully by slow solvent evaporation having water and methanol as solvent. The structure of the crystal is verified by single X-ray analysis. Optical absorption shows that the crystal is highly transparent between 1500 and 300 nm. Microhardness of the crystal is found to increases with increase in load and the hardness number is found to be high for methanol grown crystal as compared to the water grown crystal. Electrical conductivity as evaluated from the cole-cole plot is found to be 1.26 × 10⁻⁵ mho m⁻¹. The dielectric constant of the crystal is low and independent at higher frequencies. The crystal has prominent photoconduction in the presence of trap energy levels formed by the Na⁺ ions. The SHG efficiency of the crystal is studied by performing Kurtz powder test and the results of scanning electron microscope analysis indicate that the major part of the crystal surface is free from inclusion and dislocation.     

低温高压下的Na5Eu(WO4)4的发光和晶体场参数

用低温金刚石对顶砧高压显微光谱系统在20—300K低温和0—10GPa高压范围内研究了白钨矿型化学计量的基质发光晶体四钨酸铕钠Na₅Eu(WO₄)₄中Eu³⁺的发光.确定了Eu³⁺荧光谱线和能级在低温下的压力移动率.它随温度变化,表明温度和压力对Eu³⁺谱线作用不是独立无关的.按晶体场理论简化方法推导了能级的晶体场参数表达式,并按实验数据拟合出在不同低温下晶体场参数随压力的移     

Origin of the multiferroicity in BiMn2O5 from first-principles calculations

Electronic structure, Born effective charges, and spontaneous polarization of multiferroic single crystal BiMn₂O₅ have been investigated in the framework of density functional theory. The relative stability of the ground state and the origin of multiferroicity for magnetism and ferroelectricity are addressed. The results reveal that the stability of antiferromagnetic (AFM) state is better than the ferromagnetic (FM) and ferrimagnetic configurations. The Born effective charge tensors (Z^?) have been calculated for this compound using a Berry-phase approach, compared to their nominal ionic values, the Z^* of Mn atoms show anomalous difference. By investigating the electric structure of BiMn₂O₅, there exists obviously hybridization between Bi 6s and O 2p states, our calculations indicate that the 6s² lone pair on the formally trivalent Bi ion plays an important role in inducing the ferroelectric distortion.     

镱、钠共掺的氟化钙晶体在1050nm的可饱和吸收作用

通过在稳定连续波运转的Yb:YAG 激光器中插入不同掺杂浓度的新型钠、镱共掺的氟化钙晶体的对比性实验,证明了镱、钠共掺的氟化钙晶体在1050nm具有明显的可饱和吸收作用,从而解释了该晶体作为增益介质在该波段总是趋于自调Q运转的原因.Yb³⁺离子是该晶体可饱和吸收作用的主要因素,但是共掺入适当的Na离子可以明显改善晶体的调Q效果.优化共掺镱、钠离子的浓度和比例后的氟化钙晶体能够作为1050nm波段激光器的被动Q开关. 关键词： 镱、钠共掺氟化钙 可饱和吸收体 调Q     

V2Ga5的晶体结构

本文利用单晶与粉末衍射方法测定了V₂Ga₅的晶体结构。V₂Ga₅属四方晶系,其单相区约为VGa₂—V₂Ga₅。在18℃的点阵常数是a=8.9540?,c=2.6892?,每个晶胞含有二个化合式量,空间羣为D_4h⁵—P4/mbm。V原子与Ga原子分别占据在4(h)与8(i),2(d)的等效位置上。参数为:x相似文献   

Synthesis, crystal structure, thermal and dielectric properties of bis(p-phenylenediammonium) chloride hexachlorobismuthate(III) monohydrate [C6H4(NH3)2]2ClBiCl6.H2O

Synthesis, crystal structure, and dielectric properties of [C₆H₄(NH₃)₂]₂ClBiCl₆.H₂O are reported. The compound crystallizes in the monoclinic system with space group P2₁/n. The unit cell dimensions are a = 9.836(5), b = 19.582(5), c = 13.082(5) ?, β = 104.731(5)° with Z = 4. The atomic arrangement can be described by an alternation of organic and inorganic layers. The anionic layer is built up of octahedral of [BiCl₆]^3- arranged in sandwich between the organic layers. The crystal packing is governed by means of the ionic N–H···Cl hydrogen bonds, forming a three-dimensional network. The dielectric properties have been investigated at temperature range from 297 to 410 K at various frequencies (10 Hz–100 kHz). Dielectric studies were performed to confirm results obtained with thermal analysis. The evolution of dielectric constant as a function of temperature and frequency of single crystal has been investigated in order to determine some related parameters.