Mn2+、N2-共掺杂Zn2GeO4晶体电子结构和光学性质的研究

采用基于密度泛函理论的平面波超软赝势方法对本征Zn2GeO4，Mn2+掺杂Zn2GeO4，Mn2+/N2-共掺杂Zn2GeO4超晶胞进行了几何结构优化，计算了掺杂前后体系的晶格常数、能带结构、态密度和光学性质。结果表明，Mn离子掺入后，Mn离子3d轨道与O离子2p轨道之间有强烈的轨道杂化效应，掺杂系统不稳定，而Mn/N离子共掺后，Mn离子和N离子之间的吸引作用克服了Mn离子之间的排斥作用，能够明显地提高掺杂浓度和体系的稳定性。光学性质计算结果表明，Mn离子与N离子共掺杂能改善Zn2GeO4电子在低能区的光学跃迁特性，增强电子在可见光区的光学跃迁；吸收谱计算结果显示，Mn离子与N离子掺入后体系对低频电磁波吸收增加。     

高温无铅BaTiO_3-(Bi_(1/2)Na_(1/2))TiO_3正温度系数电阻陶瓷阻抗和介电谱分析

采用固相反应法制备了Y2O3施主掺杂的92 mol%BaTiO3-8 mol%(Bi1/2Na1/2)TiO3(BBNT8)高温无铅正温度系数电阻(positive temperature coe?cient resistivity,PTCR)陶瓷.利用透射电镜观察材料的显微结构,发现陶瓷的显微结构主要包括晶粒和晶界两部分,观察不到明显的壳层结构.进一步利用交流阻抗谱研究了陶瓷的宏观电学性能,发现陶瓷的总电阻是晶粒和晶界两部分的贡献,而晶粒电阻很小,在居里温度以上变化不大,材料的PTCR效应主要是晶界部分的贡献.当温度高于居里温度时,随着温度的升高,晶界介电常数逐渐减小,导致势垒增加,晶界电阻增大,从而产生正温度系数效应.最后,通过测试材料的介电频谱特性,研究计算了陶瓷的室温电阻率.     

(La1-xCex)2/3Ca1/3MnO3体系的输运性质和反常磁特性研究

本文报告了对Ce掺杂锰氧化物(La1-xCex)2/3Ca1/3MnO3 (x=0～1.0)系列样品的输运特性和反常磁特性的研究结果.实验表明,Ce掺杂对Tc有明显的抑制作用,整体上电阻率随Ce掺杂含量增加而上升,在外加磁场时表现出极大的磁电阻效应.磁化强度随温度变化的曲线出现了两个转变,高温处对应于Mn离子磁矩的铁磁金属转变,低温处的转变则对应于Ce离子磁矩自旋有序排列的形成.表明Ce掺杂引起样品中铁磁双交换作用和反铁磁超交换作用之间的竞争,Ce离子与Mn离子有很强的相互作用.随Ce掺杂含量的增加,铁磁有序转变温度下降,而反铁磁有序转变温度则向高温处移动,铁磁区域明显减小.     

Ca掺杂对CuCrO_2薄膜形成和电学特性的影响

采用溶胶凝胶法制备CuCrCaO2薄膜,研究不同气氛、退火温度下,Ca掺杂量对薄膜的形成和电学特性的影响.在N2环境中1 100℃退火,制得CuCr1-xCaxO2(x=0、0.01、0.03、0.05、0.07)薄膜.测量CuCrCaO2薄膜的X射线衍射,在低浓度Ca掺杂时,薄膜结晶良好,晶格常数a、c和平均晶粒尺寸n随掺杂浓度上升而上升;高浓度Ca掺杂时,有杂相生成,a、c、n重新变小,和X射线衍射分析结果相吻合.另将3%Ca掺杂量,分层旋涂后的薄膜分别在空气和N2中以不同温度快速退火,X射线衍射表明在N2条件下,分层次的掺杂使CuCrCaO2结晶取向趋于单一,并且退火温度越高,择优取向越明显.用霍尔仪测量不同Ca掺杂量薄膜的电学特性,x=0.03时薄膜有最佳电导率1.22×10-1S/cm,比未掺杂的薄膜提高了三个数量级,说明适量Ca掺杂有助于提高薄膜电导率,对应的薄膜载流子迁移率为1.77×1018cm-3,正的霍尔系数表明该材料是P型结构.     

微波法制备Mn2+掺杂ZnSe纳米材料及谱学性能研究

过渡金属掺杂的Ⅱ-Ⅳ族纳米材料有望替代CdSe类量子点作为新型的荧光标记物而受到广泛关注.利用微波加热法的体加热特点,以不同有机胺为配体溶剂,控制反应条件,制备了Mn2+掺杂的ZnSe纳米材料,并分别利用TEM、EDS、荧光光谱等手段对其形貌、结构和性能的关系进行了探索.Mn2+掺杂的纳米ZnSe粒子为200～500 nm的球形粒子,表面平整,为单晶的纤锌矿结构.掺杂后纳米粒子的发射峰显示Mn2+的跃迁发射,但不同的配体溶剂和掺杂量对产物的发光性能有明显影响.     

(La_(1-x)Ce_x)_(2/3)Ca_(1/3)MnO_3体系的结构和输运性质研究

对Ce掺杂锰氧化物 (La1 -xCex) 2 3Ca1 3MnO3(x =0— 1.0 )多晶样品的结构和输运性质系统研究的结果 .实验表明 ,在低掺杂浓度下 ,样品呈现完整的正交钙钛矿结构 ;随掺杂浓度的增加 ,有少量CeO2 杂相出现 ,同时伴随有Ce3 和Ce4 离子两种价态的涨落和Mn2 Mn3 Mn4 混合价态的共存 ,Ce掺杂导致的体系无序度增加 ,使得绝缘体 -金属 (I M)和顺磁 -铁磁 (PM FM)转变温度向低温方向移动 .有趣的是 ,Ce掺杂样品的电阻率测量I M转变峰值温度TIM 较PM FM转变温度Tc 为高 ,其差值ΔT(=TIM -Tc)随Ce掺杂含量的增加而增加 ,最大差值ΔT达 5 0K .各样品的磁电阻则随温度的降低而增加 ,在Tc 附近MR达到最大值 ,且随Ce掺杂含量增加Tc 附近的MR最大值迅速增加 ,达到 10 4 %以上 ,表现出很强的庞磁电阻效应 .在x≥ 0 .7时 ,磁电阻效应则表现出反常减小 .整体上而言 ,各样品的磁特性与输运行为间有较强的关联 ,电输运特性可用双交换作用模型进行很好的解释 ,在高温区满足热激活模型 .最后 ,在Ce掺杂对Tc 和MR的影响机理方面进行了初步讨论 .     

一维Mn2+掺杂CdS纳米晶体的水热合成及其发光性能

用水热方法合成了一维Mn2 掺杂CdS纳米晶体.产品分别用SEM,EDS,XRD,TEM,HRTEM和PL等技术进行了表征.结果表明,掺杂Mn2 完全替代了CdS晶格中Cd2 的位置,产品具有较好的结晶性.荧光光谱中,CdS纳米晶体表面缺陷态的发射峰被完全抑制,只能观察到单一的Mn2 的发射峰.     

退火对Mn和N共掺杂的Zn0.88Mn0.12O:N薄膜特性的影响

以NH₃为掺N源,采用电子束反应蒸发技术生长了Mn和N共掺杂的Zn_1-xMn_xO:N薄膜,生长温度为300℃,然后在O₂气氛中400℃退火0.5 h.X射线衍射测量表明,Zn_0.88Mn_0.12O(Mn掺杂)薄膜或Zn_0.88Mn_0.12O:N(Mn和N共掺杂)薄膜仍具有单一晶相纤锌矿结构,未检测到杂质相 关键词： ZnO薄膜 Mn和N共掺杂 电学特性 磁特性     

La_(2/3)Ca_(1/3)Mn_(1-x)Fe_xO_3电磁输运性质和电子自旋共振谱的研究

用固相合成法制备了La2/3Ca1/3Mn1-xFexO3(x=0、0.1、0.2)材料,通过X射线衍射、磁化强度-温度曲线、电子自旋共振谱线,研究了Fe替代部分的Mn对La2/3Ca1/3Mn1-xFexO3电磁性质的影响.结果表明:Fe离子掺杂对晶体结构影响较小;对电磁输运性质和磁结构影响较大,体系在低温区域较宽的温度范围内显示出巨磁电阻效应;ESR的测量结果也表明Fe离子掺杂形成反铁磁的交换作用,阻塞了铁磁Mn3+-O-Mn4+双交换通道,降低了体系的铁磁性.     

ZnS:Mn纳米晶的制备及其发光性能研究

以C19H42BrN为表面活性剂,采用水热法合成了ZnS:Mn纳米晶,分别利用XRD、TEM、荧光光谱仪对其物相、形貌及光学性能进行了研究。结果表明:ZnS:Mn纳米晶为闪锌矿ZnS结构,颗粒近似球形,平均粒径为4～8 nm。荧光光谱显示,ZnS:Mn纳米晶的荧光发射峰强度随着Mn2+掺杂浓度和表面活性剂含量的增加而逐渐增强。     

Tunable Ba_0.5 Sr_0.5 TiO₃ film bulk acoustic resonators using SiO₂ /Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias(< 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum(Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

Structural and microwave properties of (Ba,Sr)TiO3 films grown by pulsed laser deposition

The relationship between the structure and the microwave dielectric properties of epitaxial Ba_0.5Sr_0.5TiO₃ (BST) films has been investigated. Single-phase BST films (40-160 nm) have been deposited onto (100) MgO substrates by pulsed laser deposition. As-deposited films show a significant tetragonal distortion. The in-plane lattice parameters (a) are always larger than the surface normal lattice parameters (c). The tetragonal distortion depends on the thickness of the films and the post-deposition annealing conditions. Films annealed at 900 °C show less tetragonal distortion than the as-deposited film and the films annealed at higher temperatures. The distortion in the film is due to stress caused by the lattice mismatch and thermal expansion coefficient differences between the film and the substrate. The dielectric constant and its change with dc bias voltage of BST films on MgO at microwave frequencies increase with increasing annealing temperature from 900 °C to 1200 °C, which corresponds to an increase in the tetragonal distortion.     

The electronic and magnetic properties of （Mn,C）-codoped ZnO diluted magnetic semiconductor

The electronic and magnetic properties of (Mn,C)-codoped ZnO are studied in the Perdew-Burke-Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic (FM) interaction without acceptor co-doping. We observe that the FM interaction for (Mn,C)-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, we demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the (Mn,C)-codoped ZnO is FM semiconductor with super-high Curie temperature (T C = 5475 K). These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.     

纳米BST薄膜的制备及其折射率特性.

" 采用射频磁控溅射法在石英衬底上沉积了纳米BST(Ba0:65Sr0:35TiO3)薄膜．为了制备优质的BST薄膜,借助X射线衍射仪、场发射扫描电镜和原子力显微镜研究了BST薄膜的晶化行为和显微结构．结果显示在衬底温度600 ℃下制备的BST薄膜经700 ℃退火处理后,具有较强的特征衍射峰和极好的晶化．同时还研究了纳米BST薄膜的制备参数和特性,BST薄膜的折射率是由测量的透射谱中获得的．实验结果表明：纳米BST薄膜的沉积参数对其折射率特性的影响是不尽相同的．折射率随着衬底温度的上升而增加;在较低的溅射     

Emergence of the sub‐THz central peak at phase transitions in artificial BaTiO3/(Ba,Sr)TiO3 superlattices

A prominent central peak in the sub‐THz frequency range was observed in the Raman spectra of BaTiO₃/(Ba,Sr)TiO₃ (BT/BST) superlattice grown on (001)MgO substrate. Both soft and central mode show an anomaly around 200 K and 280 K, which can be correlated with orthorhombic to monoclinic phase transition of BST and BT, respectively. The observed temperature dependence of the central mode enabled us to explain rather broad temperature dependence of the dielectric permittivity previously observed in BT/BST superlattices. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Co和Mn共掺杂ZnO铁磁性的第一性原理

基于密度泛函理论(DFT)的总体能量平面波超软赝势方法,结合广义梯度近似(GGA),对Co单独掺杂ZnO和(Co,Mn)共掺杂ZnO的32原子超原胞体系进行了几何结构优化,计算了纤锌矿结构ZnO、Co-ZnO及(Co,Mn)共掺杂ZnO的能带结构、电子态密度,并对此进行了详细的分析。计算结果表明,ZnO中单独掺杂Co元素显示出铁磁性行为,Mn的引入减弱了Co-ZnO的铁磁性。     

Radiation trapping effects in Cu, Mn, Ca, Sr, and Ba vapor lasers

The radiation trapping effect was investigated in Cu, Mn, Ca, Sr, and Ba vapor lasers with a cylinder discharge tube. Compared with the negligible impact induced by the gas temperature, the lower level population density of radiation trapping was found to dominate the effective spontaneous emission probability. Meanwhile a tube radius scanning from 1 mm to 20 mm revealed that the threshold parameters of radiation trapping effect were affected little by the tube radius when the radius changed from 20 mm to 5 mm, but they varied visibly when the tube radius decreased from 5 mm to 1 mm. Furthermore, the threshold temperature and the lower level population density of the radiation trapping effect in six resonant lines in Cu, Mn, Ca, Sr and Ba vapor lasers were calculated, and the threshold temperature was found to be close to the initial lasing temperature of the corresponding resonance level to metastable level transition.     

X射线荧光光谱法测定花草茶中22种元素

采用粉末压片法制样,应用X射线荧光光谱法对花草茶中N,Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Cr,Mn,Fe,Ni,Cu,Zn,Br,Rb,Sr,Ba,Pb共22种元素进行了分析。讨论了测量条件的选择,对于22种目标元素的分析线,除Ba,Pb采用L线外,其余都选择K_α线,在对Rh靶K_α线的康普顿散射进行测量时,应适当降低管电压,选择合适的管电流。采用经验系数法和3条散射谱线(Rh靶L_α线的瑞利散射、0.1876nm处的散射线、Rh靶K_α线的康普顿散射)作内标进行基体效应校正,并对N,Na,Ca,Ti,Mn,Sr,Ba等部分元素进行了谱线重叠干扰校正。实验结果表明,该方法对N,Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Cr,Mn,Fe,Ni,Cu,Zn,Br,Rb,Sr,Ba,Pb各目标元素的检出限较低,且准确度较好,精密度较高。采用该方法对花草茶中元素的种类和含量信息进行分析发现,花草茶元素组成较为丰富,不同种类花草茶元素种类和含量有差异,且同一种类不同来源花草茶略有差异,但元素组成含量特征大体相似。综上可知,该方法操作简单,能够实现花草茶的低成本、快速、准确、多元素测定。     

Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

非晶钛酸锶钡薄膜的金属有机分解法制备及其光学性能

本文采用2-辛酸钡(Ba(C₈H₁₅O₂)₂)和3-甲基丁基醋酸盐(CH₃COOC₂H₄CH(CH₃)₂-)为基的特殊前驱体溶液,在硅和石英基片上低温制备Ba_0.7Sr_0.3TiO₃ (BST0.7)薄膜.性能测试结果表明,厚度约为214 nm的非晶BST0.7薄膜的光学带隙能和折射率分别为4.27 eV和n=1.94.薄膜在可见光和近红外区域的消光系数远远低于多晶BST薄膜,约为10^-3数量级.激发波长为450 nm时,在室温环境下非晶BST0.7薄膜在波长520—610 nm处发出强烈的可见光,峰值为540—570 nm,而结晶态的BST0.7薄膜则无发光现象. 关键词： 钛酸锶钡 非晶薄膜 金属有机分解法 光学性能