Ba0.5Sr0.5Co0.8Fe0.2O3-δ晶格缺陷、电性能与氧渗透研究

对新型氧渗透材料Ba0 .5 Sr0 .5 Co0 .8Fe0 .2 O3 -δ(BSCF)进行了O2 TPD表征、非化学计量 (δ)测定、电导率 (σ)测量和氧渗透性能测试的研究 .结果表明 ,经纯氧气氛处理后的BSCF ,其O2 TPD谱存在三个失氧峰 :低温峰对应于晶格中V O 位置上的吸附氧 ,高温区两个峰对应于晶格中两种不同位置的晶格氧 ;σ对温度的实验表明 ,不论在升温还是降温过程中 ,σ在 470℃左右均出现极大值 ,可能与BSCF体系的δ值随温度变化相关 ;氧渗透实验表明 ,850℃以上 ,BSCF的氧渗透率JO2 较大 ,达到 1μmol/cm2 s ,活化能较低 ,Ea =63 .1kJ/mol ,而低于 850℃时 ,存在相分解     

Ba2+掺杂对Sr3Al2O6:Eu2+红色荧光粉发光性能的影响

采用高温固相法合成了(Sr1-x-yBax)3Al2O6∶3yEu2+红色荧光材料,通过XRD、荧光光谱和热稳定性测试分析,分别研究了Eu2+、Ba2+掺杂对样品的晶体结构、发光性能和热稳定性的影响。XRD测试结果表明,在1 200℃保温3 h条件下合成了具有立方晶体结构、空间群为Pa3的Sr3Al2O6纯相样品,Eu2+、Ba2+的掺入并没有改变其基质晶格的结构类型。荧光光谱分析表明,Eu2+的摩尔分数为4%时,(Sr0.98-yBa0.02)3Al2O6∶3yEu2+样品的发射峰最强,Ba2+的掺入使样品的发射峰发生红移而发射强度降低,且随Ba2+浓度的增加红移越发明显。此外,Ba2+的掺杂提高了Sr3Al2O6∶Eu2+样品的热稳定性。     

薄膜光学 薄膜光学理论与膜系设计

O484.1 2005010406 R.F.溅射Ba0．5Se0．5TiO3／RuO2薄膜及其介电特性研究= Dielectric propertics of sputtered Ba0.5 Sr0.5 TiO3 thin film on RuO2 bottom electrode[刊,中]／张柏顺(湖北大学物理学与电子技术学院．湖北．武汉(430062)),章天金…∥光电子技术与信息,-2004,17(2).-19-22 用R.F．磁控溅射法在p-Si(100)衬底上沉积Ba0.5 Sr0.5TiO3／RuO2异质结,BST薄膜的晶相和表面形貌用 XRD和SEM分析,表明在衬底温度为550℃时。薄膜的结晶度高、表面粗糙、晶粒较大。电容器InGa／BST／RuO2的     

相场法模拟第二相颗粒对柱状晶形成的影响

基于定向退火条件下的移动热区模型,采用相场法研究第二相颗粒对多晶材料中柱状晶结构形成的影响.结果表明:第二相颗粒对柱状晶结构的形成具有抑制作用,其抑制作用随第二相颗粒体积分数的增加和第二相颗粒尺寸的减小而增强.定向退火条件下第二相颗粒对晶粒极限尺寸的影响遵循Zener关系.为了获得良好的柱状晶结构,应尽量减少材料中第二相颗粒的体积分数及其在晶界上的弥散分布.     

Ba2+取代及助熔剂对Sr3SiO5:Eu2+结构和发光性能的影响

采用还原气氛下的高温固相法制备了Sr3SiO5:Eu2+橙色荧光粉,利用X射线衍射、扫描电子显微镜和荧光分光光度计考察了Ba2+与Sr2+替换和助熔剂对Sr3SiO5:Eu2+晶体结构和发光性能的影响。结果表明:Ba2+取代Sr2+会使配位多面体膨胀,导致附近Eu2+占据的配位多面体压缩,晶体场强度增大。随着Ba2+取代量的增加,Eu2+逐渐占据Ba2+取代后的多面体中心,晶体场强度减弱,发射光谱峰值整体先由575 nm红移至592 nm后又蓝移回583 nm。Sr2+与Ba2+的量比n(Sr):n(Ba)=4时,发射光谱红移效果最佳。助熔剂H3BO3的掺入会使Sr3SiO5:Eu2+的发光强度急剧下降。而NH4F和NH4Cl掺入都能使Sr3SiO5:Eu2+的发射光谱强度增大,NH4F和NH4Cl单掺质量分数分别为2%和0.3%时增强效果最好,且NH4Cl的增强效果比NH4F要好很多。     

新型1223相高T_c超导层型铜氧化物(Tl,M)(Sr,Ba)_2Ca_2Cu_3O_z(M=Cr,V)

纯的TlSrCaCuO体系难以制备1223型超导铜氧化物,报道了合成和用粉末X射线衍射、电子衍射鉴定了一大类新型1223相高T_c超导层型铜氧化物(Tl_(1_x)M_s)(Sr_(2_y)Ba_y)Ca_2Cu_3O_x,其中M为Cr或V,包括(Tl_(0.75)Cr_(0.25)(Sr_(2_y)Ba_y)Ca_2Cu_3O_x,(Tl_(0.75)V_(0.25))(Sr_(2_y)Ba_y)Ca_2Cu_3O_x,(Tl_(1_x)Cr_x)Sr_2Ca_2Cu_3O_x和(Tl_(1_x)V_x)Sr_2Ca_2Cu_3O_5等4个系列1223相层型铜氧化物。在M存在的情况下,适量的Ba部分取代Sr,有利于(Tl,M)基1223相化合物的形成,然而,当y=0,即无Ba存在时,过量Tl对(Tl,M)基1223相化合物的形成十分必要。电阻和交流磁化率测量都显示,有Ba存在时的这些化合物超导电性T_c(ρ=0)均在100K以上,(Tl_(0.75)Cr_(0.25))(Sr_0.5Ba_1.50)Ca_2Cu_3O_x的T_c(ρ=0)可达113K,纯Sr系列掺V1223相化合物的超导电性略高于相应的掺Cr的化合物的超导电性,其中(Tl_0.75V_0.25)Sr_2Ca_2Cu_3O_x的T_c(ρ=0)可达105K。此外,作者还详细研究和讨论了M(Cr或V)量和Sr/Ba比对(Tl,M)基1223型铜氧化物形成和超导电性的影响。     

Co掺杂的YBa2Cu2O6+δ的氧非计量和氧渗透性能研究

研究钴离子部分取代铜离子对YBa2 Cu3 O6+δ的氧非计量值δ和氧渗透率的影响 .对于钴替代的样品 ,氧非计量的绝对值变大 ,且其数值不再随温度和氧分压的变化发生显著变化 .YBa2 Cu2 CoO6+δ样品在中、高温具有可观的氧渗透率 .对于厚度为 1.2mm的致密YBa2 Cu2 CoO6+δ样品 ,在 85 0℃时 ,只要在样品两端施加较小的氧分压差(PO2 =2 1.2kPa、PO2 =10 1Pa) ,其氧渗透率即可达 5 7μmol/cm2 s,明显高于YBa2 Cu3 O6+δ的氧渗透率 (31μmol/cm2s) .YBa2 Cu2 CoO6+δ的高氧渗透率在结构上可被归结为位于晶胞基面上的氧离子和氧空位的均匀分布     

Ho3+掺杂的Ba0.8Sr0.2TiO3厚膜的发光特性

用丝网印刷法在氧化铝衬底上制备了Ho3+掺杂的Ba0.8Sr0.2TiO3(BST)厚膜.XRD谱表明,随着Ho3+掺杂摩尔分数从0.5%增加到2.0%,BST厚膜的晶格尺寸先增大后减小.在514 nm的氩离子激光激发下,样品均出现了中心波长为549,650,753 nm的发光带,分别对应于Ho3+离子的(5F4,5S...     

Bax Sr1-x TiO3 精细结构的第一性原理研究

为了研究钛酸锶(SrTiO3,ST)中随Ba的掺入,其晶体从顺电相到铁电相的变化过程及四方相钛酸锶钡(BaxSr1-xTiO3,BST)的铁电性.在广义梯度近似下,利用超软赝势平面波方法计算了不同Ba/Sr摩尔比BST的总能量,确定了BST的精细结构.结果表明,在钛酸锶晶体中,随着Ba的掺入,晶胞体积膨胀, c/a比值增大,有利于晶体结构中正负离子的分离和自发极化的产生.在四方相Ba0. 8Sr0. 2TiO3 中, Ti离子沿[001]方向发生了8pm的偏心位移,从而表现出四方相BST的铁电性.     

BaF2替代BaO 对钡镓锗酸盐玻璃光学性质的影响

在摩尔分数组成x(BaO),r(Ga2O),r(GeO2)为0．20,0．15,0．65的玻璃中,分别以摩尔分数0．05,0．10．0．15和0．20的BaF2替代BaO,研究了氟化物对玻璃折射率和光吸收性质的影响。结果表明,在玻璃中加入氟化物．玻璃折射率和色散降低,玻璃的紫外吸收边向短波侧迁移,而红外吸收边无明显变化。不含氟化物的氧化物玻璃中含有大量的OH基．这些OH基在2．24μm、2．97μm和4．23μm附近引起光吸收．在含氟化物的玻璃中,2．24μm的吸收峰消失,而2．97μm和4．23μm附近的吸收大大减弱。讨论了各OH基吸收峰的起源,利用计算机技术对2．97μm附近的OH基吸收峰进行了高斯峰分离。玻璃在2．24μm的弱吸收可能来自H2O分子的一个伸缩模和两个振动模的结合(p 2ρ)．4．23μm吸收带是由与非桥O形成强氢键的OH基(T-OH…O^--T)伸缩振动引起,而中心位于2．7～3．2μm的OH吸收带为受不同程度氢键影响的OH基伸缩振动吸收．这些吸收带叠加导致OH吸收带出现非对称性加宽,吸收中心随玻璃中OH含量不同发生移动。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.