ELECTROCHEMICAL OXIDATION OF La2CuO4 SINGLE CRYSTALS

Bulk superconducting La₂CuO_4+δ single crystals are obtained by using electrochemical intercalation technique from the as-grown insulating samples. Oxidation is carried out by constant current I=10μA at temperature T=70℃ and room temperature, respectively. Structure and magnetic properties are studied by low-temperature X-ray diffraction and susceptibility measurements. A superconducting phase with T_c of 19K and δ-0.12 can be attributed to the formation of oxygen clusters. Room temperature oxidation is inhomogeneous: two superconducting phases with T_c1 of 24K and T_c2 of 8K and an antiferromagnetic phase are coexisting in the crystal. It is found that the appearance of T_c in this system has the "step" tendency.     

薄膜厚度对La1.85Sr0.15CuO4薄膜结构和超导电性的影响

使用直流同轴磁控溅射法,在SrTiO₃(STO)衬底上成功制备出c取向的La_1.85Sr_0.15CuO₄(LSCO)超导薄膜.通过电输运测量系统和X射线衍射仪研究了薄膜厚度对LSCO(x＝0.15)薄膜电学性质和晶体结构的影响.实验证明随着膜厚增加,(006)衍射峰的半高宽(Full Width at Half Maximum,FWHM)逐渐减小,薄膜的取向性增强,与此同时,薄膜的超导转变温 关键词： 1.85Sr_0.15CuO₄薄膜')" href="#">La_1.85Sr_0.15CuO₄薄膜 超导电性 晶体结构     

Zn,Ni,Mg高掺杂La1.85Sr0.15CuO4的晶体结构比较

对Zn,Ni,Mg高掺杂的La_1.85Sr_0.15CuO₄(LSCO)超导体的X射线衍射谱进行了仔细的分析,从而获得了各掺杂样品的晶格常量、原子结构参量及衍射的峰形参量,比较了不同掺杂所引起的晶体结构的差异,计算了由于掺杂所产生的晶格内部的微应变,结果表明非磁性金属Zn,Mg掺杂比磁性金属Ni掺杂更强烈地抑制了LSCO的超导电性可能与材料中晶格的微应变有关. 关键词： 1.85Sr_0.15CuO₄')" href="#">La_1.85Sr_0.15CuO₄ 磁、非磁掺杂 原子结构参量 晶格微应变     

Nd1.85Ce0.15CuO4－δ单晶c-轴方向电阻的低场行为

采用自助熔剂缓冷法成功地生长出了Nd_1.85Ce_{0. 15}CuO_4-δ单晶，其零场下零电阻温度约为21K. 在0—0.5T范围内分别测量了磁场平行和垂直样品表面的电阻转变曲线以及0.5T不同角度下的电阻转变曲线. 结果显示磁场平行和垂直样品表面时的转变温度T_p随磁场的变化均服从H=H₀(1-T_p(h)/T_p(0))²关系. 0.5T 关键词： 1.85Ce_0.15CuO_4-δ单晶')" href="#">Nd_1.85Ce_0.15CuO_4-δ单晶 输运性质     

电子型掺杂高温超导体La2-xCexCuO4飞秒时间分辨动力学研究

利用飞秒时间分辨光抽运探测技术研究了电子型掺杂La_2-xCe_xCuO₄(LCCO)高温超导材料的准粒子超快动力学过程.得到低温(T<0.7T_c)、转变温度附近(0.7T_c≤T≤T_c)和高温(T>T_c)三个温区内的动力学行为.研究发 关键词： 电子型掺杂高温超导体 飞秒时间分辨 准粒子 声子瓶颈     

Co(S1-xSex)2系统中的铁磁量子相变

针对Co(S_1-xSe_x)₂系统在x=0.11附近发生的铁磁金属到顺磁金属相变,制备了一系列不同Se替代浓度的多晶样品.通过对其结构和电阻率-温度ρ(T)关系的系统观测,结果发现,样品铁磁相变温度T_C随着Se替代浓度x值的增加,以(1-x)^1/2关系单调下降,其二级铁磁相变转变为一级相变 关键词： 量子相变 自旋量子涨落 1-xSe_x)₂')" href="#">Co(S_1-xSe_x)₂     

Ultraviolet laser-induced voltages in LaSrAlO4 single crystal

Laser-induced ultrafast photovoltaic effect is observed in LaSrAlO4 single crystal at ambient temperature without any applied bias. An open-circuit photovoltage is obtained when the wafer is irradiated by a 248-nm-KrF laser pulse of 20 ns duration. The response time and full width at half maximum of the photovoltage pulse are 6 ns and 19 ns, respectively, indicating that LaSrAlO4 single crystal has potential application in ultraviolet detector.     

C72,La2@C72几何结构和电子性质的计算研究

采用密度泛涵理论(density functional theory, DFT)中的广义梯度近似(generally gradient approximation, GGA)对富勒烯C₇₂和内掺金属La富勒烯La₂@C₇₂三种同分异构体的几何结构和电子结构进行研究.发现在C₇₂的三种同分异构体中，满足独立五边形规则(isolated-pentagon-rule，IPR)的C₇₂(D_{6d< 关键词： 72}')" href="#">C₇₂ 2@C₇₂')" href="#">La₂@C₇₂ 密度泛涵理论 几何结构 电子结构     

La0.1Bi0.9-xEuxFeO3化合物的结构与性能研究

利用固相反应烧结技术制备La_0.1Bi_0.9-xEu_xFeO₃系列化合物. 利用X射线粉末衍射进行物相鉴定和结构分析,确定了材料的相关系：x≤0.05,材料为R3c结构相;0.08≤x≤0.12,材料为赝R3c结构相;x≥0.15是Pbnm相,其中0.15≤x≤0.20区域Pbnm相存在畸变. 磁测量结果表明,材料具有弱铁磁性,对于x≤0.20材料,磁矩在x=0.12成分存在极值. 利用阻抗分析仪测量了室温介电常数随成分的变化关系.讨论了材料的结构与弱铁磁性和室温介电常数间的关系. 关键词： 0.1Bi_0.9-xEu_xFeO₃')" href="#">La_0.1Bi_0.9-xEu_xFeO₃ X射线衍射 磁性 介电常数     

Infrared active phonon modes and ionicity of single crystal MgAl2O4

Near-normal incident infrared reflectivity spectra of （100） MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the （LO-TO）1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgA1204 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.     

Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4＋ charge transfer transition

Ce^4＋-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4＋ ions doped in Ca2SnO4 occupy the Sn^4＋ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime （-83μs） for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4＋ charge transfer （CT）. The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4＋ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration （x - 0.03） is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%.     

NiS2-xSex在x=1.00附近的反铁磁量子相变

针对NiS_2-xSe_x系统在x=1.0０附近发生的反铁磁量子相变,制备了一系列NiS_2-xSe_x(x=0.96, 0.98, 1.00, 1.05, 1.10和1.20)多晶样品,对其结构、磁性质和电阻率进行了系统的观测.结果发现：样品磁化率-温度关系呈现典型的强关联电子系统特征;与铜氧化物超导体相类似,它们的电阻率-温度关系在很宽的温 关键词： 量子相变 反铁磁自旋涨落 2-xSe_x体系')" href="#">NiS_2-xSe_x体系     

Defects in Nd2CuO4 and Nd1.815Ce0.185CuO4 single crystals

We describe here four kinds of defects found in Nd₂CuO₄ and Nd_1.815Ce_0.185CuO₄ single crystals grown by the traveling solvent floating zone method. These defects include: (1) cracks, (2) inclusions, (3) gas bubbles and (4) uneven distribution of Ce⁴⁺. The formation mechanism of these defects and the measures of eliminating these defects are discussed. It is thought that the preparation of raw materials and stringent growth conditions are necessary to obtain high quality of Nd₂CuO₄ and Nd_1.815Ce_0.185CuO₄ single crystals.     

发光二极管用红色荧光粉Sr0.8-xBaxEu0.2WO4的制备和性质研究

采用化学共沉淀法制备了不同Ba²⁺掺杂浓度、 不同煅烧温度的Sr_0.8-xBa_xEu_0.2WO₄红色荧光粉. 研究了样品的晶体取向和晶格 畸变对发光性质的影响, 实验结果表明: 合成的Sr_0.8-xBa_xEu_0.2WO₄红色荧光粉为四方相, 样品中Eu³⁺的⁵D₀–⁷F₂跃迁的红光能被近紫外光和蓝光有效激发. 适量的Ba²⁺离子取代部分的Sr²⁺提高了Sr_0.8Eu_0.2WO₄荧光粉的发光强度, Ba²⁺掺杂浓度的改变对基质的晶格参数、晶体对称性和发光性能影响较大, Ba²⁺的最佳掺杂量为30%.     

Eu3+掺杂的Sr2CeO4发光材料的光致发光研究

利用高温固相反应法制备了Eu³⁺掺杂的Sr₂CeO₄样品,并对其吸附水前后的光谱特性进行了研究.结果发现,对于刚制备的Sr_2-xEu_xCeO_4+x/2样品, 在Ce⁴⁺—O^2-的电荷迁移激发中,只有强激发带(～35700cm^-1)与Eu³⁺离子间存在能量传递,而弱激发带 (～29400cm^-1)只是引起Ce⁴⁺—O^2-的电荷迁移发射;在Sr_2-xEu_xCeO_4+x/2样品吸附水后,Eu³⁺的线状吸收跃迁强度显著增加, Ce⁴⁺—O^2-两个激发带均向Eu³⁺离子传递能量. Ce⁴⁺—O^2-强激发带通过交换作用向Eu³⁺离子传递能量,而弱激发带与Eu³⁺离子间的能量传递机理是非辐射多极子近场力的相互作用. 关键词： 2-xEu_xCeO_4+x/2')" href="#">Sr_2-xEu_xCeO_4+x/2 发光性质 能量传递 吸附水     

La0.9Sr0.1MnO3薄膜中电流效应研究

用直流磁控溅射法在(100)LaAlO₃衬底上制备了La_0.9Sr_0.1MnO₃薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La_0.9Sr_0.1MnO₃薄膜在281 K处发生金属绝缘体转变.电流在0.01—4 mA范围内，薄膜的峰值电阻率随电流增大而减小，在4 mA下获得了30.5%的峰值电阻率变 关键词： 掺杂锰氧化合物 0.9Sr_0.1MnO₃薄膜')" href="#">La_0.9Sr_0.1MnO₃薄膜 电流诱导效应 相分离理论     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂 BaTiO₃(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO₃具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO₃与Tb_1-xDy_xFe_2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn∶BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m^-1偏置磁场下, Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm^-1·(80 A·m^-1)^-1.在400×80 A·m^-1偏置磁场下,Mn∶BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm^-1·(80 A·m^-1)^-1和445mV·cm^-1·(80 A·m^-1)^-1.研究表明掺杂BaTiO₃-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO₃制备的磁电效应器件颇具应用前景. 关键词： 磁电效应 双层复合材料 3')" href="#">掺杂BaTiO₃ 1-xDy_xFe_2-y')" href="#">Tb_1-xDy_xFe_2-y     

Temperature dependent phonon modes and ionicity of LiGaO2 single crystal

This paper reports that polarized far-infrared reflectivity measurements have been done on LiGaO2 single crystal along two crystalline taxes at different temperatures. The temperature dependent frequencies of the longitudinal and transverse optical phonon have been obtained from the real part of optical conductivity and the loss function respectively. A small Drude component is observed at frequency below 300 cm^-1 which could arise from Li ions or oxygen deficiencies. The ionicity of LiGaO2 has been studied from the analysis of the Born effective charge of different ions.     

组合结构化合物Ho2Ni7-xFex(x=0-3.0)的晶体结构、结构转变和磁性

在金属间化合物的结构演变中,原子尺寸因素起着重要的作用.由于密堆积效应,不同原子半径比的元素往往形成不同的结构.而自由电子填充于原子构成的晶体结构的间隙中,它对化合物的结构也有影响.基于组合结构化合物Ho2Ni7-xFex,结合原子尺寸与自由电子对晶体结构的不同影响,文章探讨一种单位体积内自由电子浓度的经验方法来判断Ho2Ni7-xFex化合物中两种异构体间的转变.随着Fe含量的增加,Ho2Ni7-xFex化合物先结晶成Gd2Co7型三方结构,然后结晶成Ce2Ni7型六方结构.利用Rietveld精修技术和磁测量,获得了化合物的晶体结构参数和饱和磁化强度.化合物晶胞常数随Fe含量增加而增加,饱和磁化强度则随之减少(dMs/dx=-2).分析结果表明,单位体积内自由电子浓度更高,化合物形成三方结构,反之则形成六方结构.     

硒化前后电沉积贫铜和富铜的Cu(In1-xGax)Se2薄膜成分及结构的比较

采用电沉积法获得了接近化学计量比的贫铜和富铜的Cu（In_1-xGa_x）Se₂（CIGS）预置层,研究比较了两种预置层及其硒化处理后的成分和结构特性.得到了明确的实验证据证明,硒化后富铜薄膜中的Cu_xSe相会聚集凝结成结晶颗粒分散在表面.研究表明：在固态源硒化处理后,薄膜成分基本不变;当预置层中原子比Cu/（In+Ga）<11时,硒化后薄膜表面存在大量的裂纹;而当Cu/（In+Ga） >12时,可以消除裂纹的产生,形成等轴状小晶粒;富铜预置层硒化时蒸发沉积少量In,Ga和Se后,电池效率已达到68%;而贫铜预置层硒化后直接制备的电池效率大于2%,值得进一步深入研究. 关键词： 1-xGa_x）Se₂薄膜')" href="#">Cu（In_1-xGa_x）Se₂薄膜 电沉积 硒化处理 贫铜或富铜薄膜