La2NiO4＋δ透氧膜材料的结构特点与性能

讨论了La2NiO4＋δ透氧膜材料的结构特点及氧渗透性能,对La2NiO4_ δ试样电子衍射谱的分析表明,其结构中由于填隙氧离子的存在及其有序化,出现了超结构现象,并根据此结构对衍射谱进行了指标化,同时探讨了结构特点与透氧机制之间的关系。     

La2O3掺杂MoSi2的SHS合成及其性能研究

以Mo粉、Si粉和La2O3为原料,通过自蔓延高温燃烧合成(SHS)的方法制备了La2O3掺杂的MoSi2材料．研究表明,掺杂剂La2O3的加入对MoSi2燃烧合成过程的热力学和动力学具有明显的影响．并通过XRD和SEM对燃烧合成产物的物相组成和形貌进行了分析,发现La2O3的加入对合成产物的物相组成没有明显影响,但可以大大降低合成产物的晶粒尺寸．同时,力学性能研究结果表明,La2O3的加入可以提高MoSi2材料的室温断裂韧性．     

La0.2Ba0.8(Co0.2Fe0.8)1-xZrxO3-δ透氧膜材料的微结构与氧分离性能研究

采用固相法制备了La0.2Ba0.8(Co0.2Fe0.8)1-xZrxO3-δ(x=0、0.05、0.1、0.15)片状陶瓷膜,用稳态法测试了不同成分制备样品的透氧性能,并利用XRD和SEM手段分析研究了样品的相结构和晶粒形貌及它们对材料性能的影响.研究表明固相法较难合成x=0的纯钙钛矿相,可用改进的Pechini法合成,另B位Zr的替代有利于去除材料中非钙钛矿杂相;x=0.1的样品中有少量BaZrO3析出,并导致晶粒细化(1～2μm),而这种微结构状态稳定且不受高温长时间退火和氧分压梯度的影响.晶粒细化样品的力学性能和氧渗透性能均有较大提高,x=0.1的样品较x=0样品的氧渗透性能提高了一个数量级,在1010℃,样品厚1.2mm时体系的透氧率达到4.6×10-7mol.cm-2.s-1.     

添加La2O3对Mg2TiO4陶瓷的显微结构与微波介电性能的影响

采用传统烧结工艺，制备了具有不同La2O3含量的镁钛镧陶瓷，并研究了La2O3组份对材料晶相构成、晶粒、晶界的演变、介电常数和品质因数的影响。结果表明，不含La2O3的钛酸镁陶瓷主晶相为Mg2TiO4，其平均晶粒尺寸＞60μm；引入La2O3后，出现新晶相La0.66TiO2.99，材料的晶粒尺寸明显下降；随La2O3含量的增加，材料的介电常数线性增加，材料的品质因数Q在10GHz出现最大值（16558）。     

混合导电体Y1-xLaxBa2Cu3O7-δ透氧膜的透氧性能研究

用稳态法研究了具有类钙钛矿结构的Y1-xLaxBa2Cu3O7-δ(x=0.1、0.3、0.5、0.8和1.0)致密透氧膜在750～1000℃之间的透氧量.实验发现,透氧速率随着La替代Y的比例x的增加而增加;在大约875℃,氧空位的有序-无序转变导致透氧率有一个突然增加.透氧膜的两侧分别为He气氛和空气,当La完全替代Y时,厚1.0mm的LaBa2Cu3O7-δ膜的透氧量达到1.22μmol/s.cm2(1.64 mL/min.cm2).     

La2O3在MgO-Al2O3-SiO2-TiO2微晶玻璃中的作用

在MgO-Al2O3-SiO2-TiO2玻璃中添加不同数量的氧化镧，采用差热分析，X射线衍射及电子显微镜等技术研究了氧化镧对玻璃析晶过程与力学性能的影响。氧化镧的加入使玻璃中析出α－堇青石相的温度降低，同时避免了高膨胀方石英相的析出。随着氧化镧加入量的增加，玻璃整体析晶能力下降，微晶玻璃中晶相含量减少，晶粒尺寸增大，微晶玻璃的弹性模量与硬度减小，断裂韧性增加，体现出大尺寸长柱状金红石晶粒的增韧作用。     

钙钛矿结构La(1-x-y)CaxSryMnO3陶瓷的制备及研究

采用溶胶-凝胶法制备了纳米La(1-x-y)CaxSryMnO3系列粉体,经压片后烧结成陶瓷.用振动样品磁强计测量样品的磁化强度随温度的变化,结果表明各样品的居里温度在250～330K温度范围内,|(e)M/(e)T|最大值在1.353～3.392A·m2/kg·K范围内变化.用差示扫描量热仪(DSC)测定了各样品相变温度和相变潜热,得出各样品的相变潜热在0.852～2.381J/g范围内,相变潜热较大的样品其|(e)M/(e)T|最大值也较大;另外,La0.8-xCao.20SrxMnO3(x=0.05、0.08、0.10)样品的|(e)M/(e)T|最大值较大,并且居里温度在室温附近,有可能成为室温附近的磁制冷材料.     

复合半导体光催化材料ZnFe2O4-TiO2/SiO2结构与光响应性能研究

采用溶胶．凝胶法制备了负载型复合半导体光催化材料ZnFe2O4-TiO2／SiO2，并通过DTA-TG、XRD、XPS、Raman、TPR及UV-Vis DRS等实验技术对复合材料的晶体结构、表面组成及光响应性能进行了表征和评价．结果表明：ZnFe2O4晶相以高分散状态存在于光催化材料的表面；ZnFe2O4与TiO2复合可使部分Fe^3＋进入体相TiO2的晶格中，促进其由锐钛矿向金红石的相转变，同时表面剩余的少量Zn计聚集形成ZnO物相；TiO2的相变由体相开始，随着ZnFe2O4含量的增加逐渐向表面扩展；SiO2的加入使活性组分更加分散，TiO2平均粒径〈10nm；ZnFe2O4的加入明显拓宽了TiO2的吸光域，并增强了对可见光的吸收．     

新型La2Mo2O9基氧离子导体的研究进展

自2000年Lacorre等人报道La2Mo2O9具有较高的氧离子电导率以来，La2Mo2O9基氧离子导体由于具有优异的性能而受到人们的关注．本文综述了新型氧离子导体La2Mo2O9的研究现状．重点介绍了纯La2Mo2O9及其掺杂体系的结构与相变、氧离子电导率、氧空位扩散机理、化学稳定性和热膨胀系数等性能．已有的研究结果表明，基于La2Mo2O9的氧离子导体可望在固体氧化物燃料电池、氧传感器、透氧膜等方面得到应用．     

La/TiO2-SiO2薄膜的光催化性能研究

采用溶胶-凝胶法制备了不同掺杂量的La／TiO2-SiO2复合薄膜．通过XRD、FE-SEM和AFM研究了复合薄膜的微观结构，采用紫外光照射下亚甲基蓝的分解实验比较薄膜的光催化性能．结果表明：La掺杂可显著提高TiO2-SiO2复合薄膜的光催化活性，以5％掺杂量为最佳，其光降解率比掺杂前提高了约23％．薄膜活性提高的主要原因是La掺杂后细化了TiO2的晶粒，提高了薄膜的比表面积，使其具有更高的氧化还原电势，La^3＋取代Ti^4＋进入到TiO2晶格，引起晶格膨胀，这种不同价离子的取代导致TiO2粒子表面电荷分布不平衡，从而提高了光生电子-空穴的分离效率．     

Thermodynamic studies of the semiconductor to metal transition in La2NiO4

Further evidence of the second-order nature of the semiconductor-metal transition in La₂NiO₄ in the range 570K < T < 680K is provided from the results of heat capacity measurements. High-temperature X-Ray crystallographic measurements show that the metallic phase undergoes a crystallographic distorition.     

Further evidence for the coexistence of localized and itinerant 3d electrons in La2NiO4

Measurement of a continuous increase in unit cell c/a ratio of La₂NiO₄ with temperature — but without change of symmetry from 77 to 773 K, refinement of the local distortion of the Ni²⁺-ion octahedral site to tetragonal ($\text{c}\text{a}\text{> 1}$) symmetry ($\text{c}\text{a}\text{= 1.027}$ at room temperature) as against a $\text{c}\text{a}\text{< 1}$ in K₂NiF₄, and determination of a constant oxygen content in air for all temperatures below 100 K provide evidence that the nickel d_z2 spin is localized whereas the d_x2?y2 electrons occupy a narrow $\text{σ1}{}_{\mathrm{<mtext>x</mtext><mtext>2?</mtext><mtext>y</mtext><mtext>2</mtext>}}$ band of itinerant-electron states containing strong electron correlations that increase with decreasing temperature.     

Analysis of Temperature Dependence of Electrical Conductivity in La2NiO4.14 Single Crystal

Electrical resistivity of La₂NiO_{4+ δ} single crystals has been investigated. Results showed several anomalies that are related to the onset of spin and charge ordering, either static or dynamic.     

Magnetic properties of metallic La2CuO4

X-ray, magnetic susceptibility, and electron paramagnetic resonance measurements have been made on La₂CuO₄. Magnetic measurements in the range 4.2 – 300 K are consistent with the metallic nature of La₂CuO₄, and the itinerant - electron susceptibility is estimated to be 239 × 10^?6 emu mol^?1. The high susceptibility and density of states indicate that the conduction band is narrow. The results are discussed in terms of previous models of the level structure of La₂CuO₄, and it is concluded that conduction occurs via a $\text{σ1}{}_{\mathrm{<mtext>x</mtext>}}\text{2}{}_{\mathrm{<mtext>?</mtext><mtext>y</mtext>}}\text{2}$ band. Comparison of La₂CuO₄ with semiconducting lanthanide cuprates suggests that this compound is on the verge of a semiconductor-to-metal transition.     

Ti掺杂BiFeO3陶瓷的结构和铁电性能研究

用固相反应法制备了BiFe_1-xTi_xO₃(BFTxO)陶瓷样品,研究了不同Ti掺杂量对BFO陶瓷结构、形貌、铁电性能和铁电-顺电相变温度(T_c)的影响. XRD结果表明,当Ti含量x从0增大到0.2,相的结构由菱方钙钛矿逐渐变为斜方结构. Raman光谱的测试和模拟也证实了掺Ti后晶体结构有向三斜晶系转变的趋势. I-V曲线说明Ti掺杂显著降低了BFO陶瓷的漏电流,当Ti掺杂量为0.05时,漏电流最小,在100V电压下,漏电流密度为7.3×10^－6A/cm². Ti掺杂还增强了BFO陶瓷的铁电性,Ti掺杂量为0.05时的剩余极化强度甚至是纯BFO的两倍. 另外,DTA测试显示,Ti掺杂能影响BFO的铁电顺电相变温度. 随着Ti掺杂量的增加,铁电顺电相变温度逐渐降低.     

Complex Phase Separation in Oxygen-Doped Cuprates La2CuO4+y Superconductors

The multiple-phase separation with coexistence of two different superconducting phases in the phase diagram of oxygen-doped La₂CuO_{4+ y} cuprates is interpreted with a modified Van der Waals scheme. The model includes the tendency of intercalated oxygen ions to form clusters at preferential densities. We obtain the coexistence and competition of two different superconducting phases with different T _c and interstitial oxygen content y, in agreement with experiments.     

Influence of Lattice Parameter Scaling on Local Electronic and Magnetic Properties in La2CuO4

A large amount of static and dynamic NMR experiments have been carried out to determine the spin properties in high temperature superconductors cuprates (HTSC). In the majority of cuprates the magnetic shift at the planar copper nucleus is independent of the temperature when the field is applied perpendicular to the CuO₂ planes and does not exhibit the expected reduction of the spin susceptibility in the superconducting state. This has been explained by a coincidental cancellation of on-site and transferred hyperfine fields at the copper nucleus, which would lead to a vanishing spin shift. To examine this explanation we determine the hyperfine fields by ab initio cluster calculations for La₂CuO₄ within the framework of spin-polarized density functional theory. In particular we investigate the sensitivity of the hyperfine fields on the lattice constants.     

The effect of pressure on the superconducting and crystallographic transitions of La3S4, La3Se4 and La3Te4

The superconducting transition temperatures (T_c's) for La₃S₄ and La₃Se₄ vary in a non-linear fashion under hydrostatic compression to 22 kbar. Both T_c and the crystallographic transformation temperature rise with pressure for La₃S₄ and show a maximum near 10 kbar for La₃Se₄. Non-transforming isostructural La₃Te₄ exhibits a linear pressure dependence of T_c. However, the telluride undergoes a pressure induced phase transformation at ～70 kbar. In this case the sign of the pressure dependence is different from the sulfide and selenide. Variation of T_c with the crystallographic transformation temperature shows a new and unexpected behavior.     

纳米La2O3:Eu的结构及其光致发光性质研究

采用共沉淀法制备出纳米级La2O3Eu.并采用相关光谱、X-射线衍射(XRD)、荧光光谱(PL)对所制备的纳米发光粉体进行表征.结果表明制备的纳米发光粉体的粒径均匀,集中在20nm左右;XRD结果证明制备的La2O3Eu粉体属于六方相,PL的结果说明La2O3Eu具有良好的发光性质.     

稀土掺杂锂锰氧化物LiMn2-xNdxO4(X=0.005～0.1)的结构和电性能研究

采用微波与传统加热相结合的方法首次合成了稀土掺杂基锂锰氧化物LiMn2-xNdxO4(x=0.005-0.1)材料，电化学性能测试结果表明材料在掺杂量为x=0.01时表现出最大放电比容量，同时具有很好的循环稳定性，经过100次循环其容量衰减仅为14.9%；XRD测试结果表明在LiMn2O4尖晶石晶格中掺入合适量的Nd对稳定尖晶石骨架结构起重要作用；FTIR分析技术揭示了容量少量衰减的原因。