Influence of annealing treatment on structural and magnetic properties of double perovskite Sr2FeMoO6

The structure, magnetic and electric properties of Sr2FeMoO6 （the as-made sample） and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance（MR） elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance （TMR） can be realized by regulating the grain size at appropriate annealing temperature.     

Microwave synthesis and characterization of new red long afterglow phosphor Sr3Al2O6：Eu

Nanoparticles of red long afterglow phosphor Sr3Al2O6： Eu^2＋ were prepared by microwave irradiation method at a power of 680 W and a processing time of 15 min. The phosphors nanoparticles were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Fluorescence spectrophotometer techniques. The results reveal that the samples are composed of single Sr3Al2O6 phase. The resultant nanoparticles show small size （80-100 nm） and spherical shape. The excitation and emission spectra indicate that excitation broad band chiefly lies in visible range and the nanoparticles emit much strong light at 612 nm under around 473 nm excitation. And the long afterglow phosphorescence of Sr3Al2O6 doped with Eu^2＋ was observed in the dark with naked eye after the removal of the excitation light. The effect of Eu^2＋ doping concentrations of the samples on the emission intensity is studied systematically. Furthermore, the microwave method requires a very short heating-time and the energy consumption.     

La0．8Ca0．2CrO3钙钛矿复合氧化物的GNP法合成与表征

采用GNP（Glycine-Nitrate Process）法合成La0.8Ca0.2CrO3初级粉料，研究甘氨酸用量对产物的晶体结构和显微形貌的影响，并测试烧结体的相对密度和电导率。研究结果表明，甘氨酸与金属离子的摩尔比（G／M^n＋）控制在2．0～2．5时可得到颗粒尺寸细小、均匀（100nm～200nm）的单相钙钛矿粉体，烧结温度为1350℃时样品的相对密度达到91．0％，测试温度为800℃时样品的电导率达到30．5S.cm^-1。与常规固相法相比，GNP法制备的样品具有更好的烧结活性和导电性能。     

溶胶-凝胶法制备Eu掺杂Sr2 MgSi2O7光致发光性能

采用溶胶-凝胶(sol-gel)法制备稀土离子Eu掺杂的Sr2MgSi2O7硅酸盐基发光材料,通过X射线衍射仪(XRD)、透射电子显微镜(TEM)、荧光分光光度计(PL)对样品的晶体结构、形貌及光学性能进行测试。XRD测试结果表明,在较低的处理温度下可获得Sr2MgSi2O7,但样品中也存在其它的杂质相。荧光光谱测试结果表明,经空气中处理的Eu3+在395 nm光激发下产生590 nm、610 nm的发射峰,通过氢气还原处理后得到的Eu2+离子的发光从250到400 nm的紫外区可以激发峰值为460 nm左右的宽谱带,且随氢气还原温度的升高和Eu离子掺杂浓度的提高发光强度也增强。     

燃烧合成法制备LaB6超细粉末及表征

采用燃烧合成法制备高纯超细LaB6粉末。考察反应物配比和制样压力等条件对燃烧产物相组成和微观结构的影响,利用XRD、SEM和EDS等技术对燃烧产物和浸出产物进行表征。结果表明,燃烧产物由LaB6,MgO和少量Mg3B2O6组成。随着制样压力的增加,燃烧产物变得致密坚硬。LaB6的纯度高于99.0%,其粒度为1.92？3.0μm,晶格常数a=0.4148nm。     

微波合成无铅压电陶瓷粉体的研究

采用了微波新技术对NBT-BT(0.94 Na0.5Bi0.5TiO3-0.06BaTiO3)基陶瓷粉体进行了预合成,研究了制粉和预合成方法、预合成温度、保温时间对NBT基陶瓷粉末的粒径、组成和结构的影响.结果表明(1)在微波预合成NBT陶瓷粉料过程中,温度和保温时间的较佳条件是800℃保温40 min.(2)与常规的马弗炉预合成方法相比,微波预合成反应温度低(800℃)、保温时间短(40 min)、加热方式均匀、制得的陶瓷预烧料粒度小(50 nm)、均匀性好、相纯度高.     

Sb对Mg-5Al-2Sr合金耐腐蚀性能的影响

采用失重法、极化曲线、电化学阻抗谱和腐蚀形貌等方法研究了微量Sb对Mg-5Al-2Sr合金在3.5 mass% NaCl中性水溶液中耐腐蚀性能的影响。结果表明,Mg-5Al-2Sr-xSb(x=0,0.3,0.6,1.0)合金在3.5 mass% NaCl中性水溶液中初期的腐蚀类型为点蚀,点蚀源于块状三元τ相和颗粒状SbSr₂相。这些相的数量越多,尺寸越大,合金的腐蚀愈严重。网状分布的Al_4Sr相能够成为合金腐蚀的有效障碍。Mg-5Al-2Sr合金中加入0.3% Sb不仅能够有效地细化α-Mg基体组织,同时促进了Al₄Sr相的形成,使该相的分布更趋网状化,该合金的自腐蚀电位明显正移,腐蚀电流密度减小,腐蚀速率降低,合金的耐蚀性能提高。     

Fe2O3-MnO2-CuO-Co2O3体系红外辐射材料的微波合成与表征

采用微波合成法制备了Fe2O3-MnO2-CuO-Co2O3体系红外辐射材料, 测量了微波合成粉料的红外辐射性能, 运用XRD, IR, SEM和图像分析等测试方法研究了合成粉料的结构和颗粒形态. 结果表明, 采用微波加热在1000℃保温10min和在900℃保温30min, 均得到立方尖晶石结构的合成产物. 与常规固相合成法相比, 微波合成温度减低, 反应时间缩短. 合成粉料的颗粒细小均匀, 平均粒度分别为1.175μm和1.814μm. 微波合成粉料的红外辐射性能与采用常规固相合成法制备粉料的红外辐射率基本相当, 其法向全辐射率均达到0.84.     

Sr变质对AlSi6Mg2半固态铝合金组织和性能的影响

利用电磁搅拌装置制备半固态浆料，研究了Sr变质对AlSi6Mg2半固态合金微观组织和力学性能的影响。结果表明：加入0．02％-0．04％Sr，不仅能够改善共晶硅形貌，而且对Mg2Si也有一定的变质作用，使合金的性能明显改善，特别是塑性提高了1倍以上。     

新型蓝色长余辉发光材料Sr2Al6O11：Eu^2＋,Er^3＋的微波合成

在微波场作用下,首次合成了蓝色长余辉发光材料Sr2Al6O11: Eu2 , Er3 ,利用XRD对其进行晶相分析,用荧光光度计测其激发光谱和发射光谱及余辉衰减曲线,利用热释光剂量仪测定其热释光谱.结果表明:该产品为正交晶系,Pnnm空间群,a= 2.191 827 nm,b=0.840 857 nm,c=0.488 175 nm,该产品激发和发射谱均为宽带谱,在270和340 nm处有2个主激发峰,主发射峰位于460 nm,Sr2Al6O11: Eu2 ,Er3 的发光余辉可持续14 h以上,Sr2Al6O11: Eu2 ,Er3 中存在2个热释峰,一个位于49.1 ℃,另一个位于140 ℃左右.2个陷阱能级分别为0.585 eV和0.806 eV.     

Nature of magnetic and electronic structure of double perovskite A2FeMoO6

The nature of magnetic and electronic structure in double perovskite structure A2FeMoO6 （A= Sr, a, Ca） was calculated using the local spin density approximation （LSDA） and the LSDA＋U Coulomb interaction method of density functional theory. The result shows that Sr2FeMoO6 is magnetic metallic material, whereas Ba2FeMoO6 and Ca2FeMoO6 are half-metallic materials. Fe has great effect on the magnetic property of double perovskite structure A2FeMoO6 materials. Because of the orbit hybridization and polarization between the metal element and O element, the Mo element has magnetic properties. The static magnetic moment of double perovskite structure A2FeMoO6 materials, the value of the magnetic moment of these A2FeMoO6 for （A=Ca, Sr, Ba） are 3.626 43μB, 2.678 64μB, 3.706 17μB, respectively. The magnetic moment of Fe element in the crystal cell are, 3.626 43μB, 2.678 64 μB, 3.706 17μB. And the energy of crystal cells are -28 540.561 907Ry, -24 268.037 272Ry, -44 106.187 179Ry, These values are in agreement with the experiment values.     

微波法合成纳米羟基磷灰石晶体及表征

以Na3PO4·12H2O,Ca(NO3)2·4H2O为前驱体,通过调节pH值控制PO43-的生成,利用微波液相法合成针状纳米羟基磷灰石(n-HA),采用X射线衍射(XRD)仪、拉曼光谱(RS)、红外光谱(FT-IR)、透射电镜(TEM)等对粉体相组成和形貌进行分析。结果表明,微波液相法可以快速合成类骨n-HA晶体,合成的n-HA晶体呈针状,尺寸在(10~20)nm×(50~70)nm之间,随着微波加热时间的延长,n-HA晶体的结晶程度升高,晶体形貌从针状向短柱状转变。     

不同微观形貌VO2的微波水热可控合成

采用一种新颖的微波水热法制备VO2粉体,利用扫描电镜(SEM)表征所合成粉体的微观形貌,调节H2O2的浓度、微波功率、微波时间、pH值、水热反应时间及钨掺杂剂等合成工艺参数,实现了对VO2粉体形貌的调控。结果表明:控制不同的工艺参数可合成具有不同形貌如球形、空心椭球形,花簇状、棒状等VO2粉体。     

Structural characteristics and dielectric properties of glass-ceramic nanocomposites of (Pb,Sr)Nb2O6-NaNbO3-SiO2

The structure and dielectric properties of(Pb,Sr)Nb2O6-NaNbO3-SiO2 glass-ceramics with different Pb and Sr contents were investigated.The XRD pattern of glass-ceramics without Sr substitution is different from that with Sr substitution,which indicates the existence of orthorhombic phase in the latter ones.TEM bright field observation shows nanosized microstructures,while for samples with Sr,typical eutectic microstructure with separated crystallized bands is found in the glass matrix.Dielectric properties measurement of the samples indicates an obvious improvement of dielectric constant,dielectric loss,DC field and temperature dependence of dielectric constant when the molar ratio of Sr to Pb is 4:6.     

Fe掺杂对Bi2Sr2Co2Oy热电性能和自旋关联的影响

采用固相合成法制备出系列Fe掺杂的Bi2Sr2Co2Oy，样品，并对样品进行XRD分析，电阻率（p）、热电势（固和顺磁共振研究。结果表明：Fe掺杂浓度x≤0．3时样品基本为单相。Fe掺杂使体系的电阻率略微增大，热电势显著升高，这可能与Fe掺杂降低了空穴载流子浓度有关。Fe掺杂浓度x=0．05样品获得最大的功率因子（power factor，S^2／P）。顺磁共振结果显示，不掺Fe的样品有着较强的顺磁共振（ESR）信号，随着Fe含量的增加，ESR信号向低频方向移动，并逐渐宽化减弱直至消失。这表明Fe掺杂改变了体系的自旋关联状态，占据了Co位参与了Co—O—Co之间的自旋关联。研究结果表明合适的元素掺杂可以有效地调整体系的自旋关联状态，改善材料的热电性能。     

B_2O_3添加对(Zn_(0.5)Mg_(0.5))Nb_2O_6陶瓷微波介电性能的影响

研究了B_2O_3助烧剂对(Zn_0.5Mg_0.5)Nb_2O_6陶瓷的烧结温度、微观结构、相结构及微波介电性能的影响.结果表明,助烧剂B_2O_3的添加有助于降低(Zn_0.5Mg_0.5)Nb_2O_6陶瓷的烧结温度,可以将(Zn_0.5Mg_0.5)Nb_2O_6陶瓷的烧结温度降低到950 ℃.其中掺杂2%B_2O_3(质量分数,下同)的(Zn_0.5Mg_0.5)Nb_2O_6陶瓷,在950 ℃烧结可获得结构致密的烧结体,并且具有较佳的介电性能:ε_r = 20.7,Q×f= 60156 GHz.     

钙钛矿型铁酸铋粉体的水热合成及表征

分别以FeCl3·6H2O和Fe（NO3）3·9H2O为铁源，Bi（NO3）3·5H2O为铋源，氨水为沉淀剂，KOH为矿化剂，采用共沉淀法制备前驱物，水热合成出纯相的BiFeO3粉体。借助X射线衍射、扫描电镜和傅里叶变换红外光谱分析，对所制备的粉体的晶相结构、显微形貌和键性进行了表征。结果表明，以FeCl3·6H2O为铁源水热制备BiFeO3粉体比以Fe（NO3）3·9H2O为铁源的合成温度更低，温度范围更宽；不同的铁源和前驱物浓度对所制备BiFeO3粉体的显微形貌影响很大；所制备BiFeO3粉体存在Fe-O键的弯曲振动和伸缩振动，表明了FeO6八面体的存在和BiFeO3的钙钛矿结构。