电脉冲对多晶La0.7Ca0.3MnO3比热的影响

对电脉冲诱导的不同电阻态下La_0.7Ca_0.3MnO₃样品的比热进行了研究.实验结果表明,电脉冲导致La_0.7Ca_0.3MnO₃样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La_0.7Ca_0.3MnO₃样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化.     

沉积于MgO基片上的La0.7Ca0.3MnO3薄膜的应变弛豫和磁电阻特性

利用90°离轴射频磁控溅射方法将La_0.7Ca_0.3MnO₃(LCMO)沉积于(001)取向的MgO单晶基片上,薄膜厚度变化范围为5nm到200nm. 通过掠入射X射线衍射技术测量了LCMO/MgO薄膜的面内晶格常数, 结合常规X射线衍射研究了LCMO薄膜的晶格应变及其弛豫情况, 用四探针法测量了薄膜的磁电阻特性.结果表明, LCMO/MgO薄膜均为(001)取向生长, 在厚度小于5nm时已经发生应变弛豫, 当薄膜厚度为100nm以上时, 薄膜的微应变接近于完全弛豫, 并表现出与块体材料类似的磁电阻特性, 具有较大的磁电阻和较高的磁电阻峰值温度.     

多晶La0.7Sr0.3MnO3的低温输运性质和磁电阻效应

详细研究了由纳米晶粒组成的块体多晶La_0.7Sr_0.3MnO₃(LSM)的电阻率和磁电阻效应,以及它们的温度依赖性.随着温度从室温降低,电阻率(ρ)在250K附近存在一最大值,低于该温度后,样品表现为金属导电特性,随后在50K附近存在一极小值.也就是说在低于50K的温度范围内,随着温度降低ρ反而升高,表现为绝缘体性的导电特性.经研究发现,这种随温度降低ρ反而增加的现象与隧穿效应的理论模型(lnρ∝T^-1/2)符合得很好 关键词： 0.7Sr_0.3MnO₃')" href="#">多晶La_0.7Sr_0.3MnO₃ 隧道效应 隧道磁电阻效应     

电脉冲对多晶La0.7Ca0.3MnO3比热的影响

对电脉冲诱导的不同电阻态下La_0.7Ca_0.3MnO₃样品的比热进行了研究.实验结果表明,电脉冲导致La_0.7Ca_0.3MnO₃样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La_0.7Ca_0.3MnO₃样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化. 关键词： 0.7Ca_0.3MnO₃')" href="#">La_0.7Ca_0.3MnO₃ 比热 氧离子迁移     

纳米多晶La0.7Sr0.3MnO3－δ的输运性质和磁电阻效应研究

利用溶胶-凝胶法制备了纳米多晶La_0.7Sr_0.3MnO_3-δ(LSM)块体样品.详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系和磁电阻效应.随着测量温度从室温降低,电阻率ρ都在250K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50K左右存在一极小值.即随着温度从50K左右降低到4.2K,ρ反而逐渐升高,表现为绝缘体性的导电特性.研究表明,在低温下(<50K),ρ随温度降低而升高的现象与隧穿效应的理论模型(lnρ∝T^1/2)符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所致.而在50—250K的温度范围内,其电阻率与T²成正比,表现为LSM本征的金属导电特性.因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.本文还详细研究了相应的隧道磁电阻效应. 关键词： 0.7Sr_0.3MnO_3-δ')" href="#">多晶La_0.7Sr_0.3MnO_3-δ 隧道效应 隧道磁电阻效应     

La0.3Sr0.7TiO3模板层对Pb(Zr0.5Ti0.5)O3薄膜的铁电性能增强效应的研究

通过sol-gel法在Si (111) 基片上分别制备了LaNiO₃(LNO)底电极和LaNiO₃/La_0.3Sr_0.7TiO₃ (LNO/LSTO)底电极.然后采用sol-gel 方法，在两种衬底上分别制备了Pb (Zr_0.5Ti_0.5)O₃ (PZT)铁电薄膜.XRD分析表明，两种PZT薄膜均具有钙钛矿结构，且在LNO底电极上的PZT薄膜呈(100) 择优取向，而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明，相对LNO衬底上制备的PZT薄膜，在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强，同时矫顽场也增大.介电常数和漏电流的测试表明，LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流. 关键词： PZT薄膜 铁电性 漏电流 0.3Sr_0.7TiO₃')" href="#">La_0.3Sr_0.7TiO₃     

La1-xSrxCoO3系列化合物的高压合成与性质的研究

 本文首次用高压手段合成出La_1-xSr_xCoO₃（x=0.0、0.2、0.3、0.4、0.6、0.8和1.0）化合物系列，最佳合成条件为2.6 GPa/1 050 ℃/40 min。通过对其结构相变与畸变程度、氧缺位问题的研究以及价态变化的讨论，得出了高压减小畸变量、增加氧缺位数并导致一部分低价态Co离子出现的结论。还讨论了上述诸因素对电导率和催化性能等的影响。     

γ-Si3N4在高压下的电子结构和物理性质研究

采用基于密度泛函平面波赝势方法(PWP)和广义梯度近似(GGA-PW91)，计算了不同压强下γ-Si₃N₄的电子结构、光学性质和力学性质.基于计算结果，分析讨论了γ-Si₃N₄各物理参数随外压力的变化规律.计算表明，γ-Si₃N₄是一种适合于在高压条件下工作的材料.     

择优取向MgO缓冲层上制备的硅基Ba0.7Sr0.3TiO3薄膜的结构和性能研究

分别采用sol-gel法和磁控溅射法在Si（001）单晶衬底上制备出（111）和（001）取向的MgO缓冲层薄膜,随后在其上生长Ba_0.7Sr_0.3TiO₃（BST30）铁电薄膜.通过X射线衍射,扫描电子显微镜,原子力显微镜等方法研究了薄膜的微结构.实验结果发现,在较厚的MgO（001）缓冲层上可长出（101）取向的BST30薄膜,而在较薄的MgO（111） 缓冲层上则表现出（101）和（111）取向相互竞争的现象,随着MgO（111）缓冲 关键词： 0.7Sr_0.3TiO₃')" href="#">Ba_0.7Sr_0.3TiO₃ 铁电薄膜 择优取向 sol-gel     

LiAl5O8高压相变研究

 运用金刚石压砧同步辐射X射线衍射,对尖晶石结构的LiAl₅O₈进行了高压原位研究。实验发现：在高压下,一组LiAl₅O₈的新相衍射峰出现,随着压力的增加,其新相衍射峰逐渐增强,当压力增加到45.0 GPa时,LiAl₅O₈的低压相衍射峰全部消失,而形成了一组高压新相衍射峰。采用指标化程序对衍射数据进行处理和分析,确定这一高压新相为正交晶系结构,其晶胞参数为a=0.995 9 nm,b=0.644 7 nm,c=0.333 4 nm ,空间群为Pmm2。     

La0.3Sr0.7TiO3模板层对Pb(Zr0.5Ti0.5)O3薄膜的铁电性能增强效应的研究

通过sol-gel法在si(111)基片上分别制备了LaNiO3(LNO)底电极和LaNiO3/Sr0.7TiO3(LNO/LSTO)底电极.然后采用sol-gel方法,在两种衬底上分别制备了Pb(Zr0.5Ti0.5)O3(PZT)铁电薄膜.XRD分析表明,两种PZT薄膜均具有钙钛矿结构,且在LNO底电极上的PZT薄膜呈(100)择优取向,而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明,相对LNO衬底上制备的PZT薄膜,在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强,同时矫顽场也增大.介电常数和漏电流的测试表明,LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流.     

Effects of crystallographic orientation on the oxygen exchange rate of La0.7Sr0.3MnO3 thin films

The oxygen surface exchange of La_0.7Sr_0.3MnO₃ (LSM) thin films was investigated using the electrical conductivity relaxation (ECR) method. Epitaxial (100)-, (110)-, and (111)-oriented LSM films were fabricated on corresponding SrTiO₃ (STO) substrates using pulsed laser deposition. The LSM films had well-controlled surface qualities, exhibited bulk-like steady-state electrical properties, and exhibited surface dominated responses in ECR. The chemical surface exchange coefficients (k_chem) were determined and varied from ≈ 1 × 10^− 6 to 65 × 10^− 6 cm/s, depending on temperature and orientation, with activation energies of between 0.8 and 1.2 eV. At 800 °C, a four fold variation is observed in the k_chem values, with (110)/(100) being the highest/lowest, explained well by the high activation energy for (110), ≈ 1.16 eV, and the low energy for (111) and (100), ≈0.83 eV.     

Study on the phase separation of La0.7Sr0.3MnO3 nanoparticles by electron magnetic resonance

In this work, the technique of electron magnetic resonance (EMR) is used to measure the magnetic resonant spectra of La_0.7Sr_0.3MnO₃ nanoparticles synthesized by sol–gel routes with three different gelation agents (S1: Urea+citric acid; S2: citric acid, and S3: Urea+tri-sodium citrate). The purpose of this study is to investigate the influence of synthesis conditions on the magnetic properties of nanoparticles. Our ESR results show that Curie temperatures of La_0.7Sr_0.3MnO₃ nanoparticles with different gelation agents are slightly different (T_c∼340 to 360 K) and possess both paramagnetic (PM) and ferromagnetic (FM) phases in the temperature below T_c. Besides, a sharp FM–PM transition indicates that the combined agent of Urea+tri-sodium citrate creates a better quality in CMR nanomagnets.     

Pulsed laser ablation of La0.5Sr0.5CoO3

The ablation process of La_0.5Sr_0.5CoO₃ by a spatial uniform 248 nm excimer laser beam has been characterized. Ablation rates, changes in the target surface morphology and composition have been studied as a function of the laser fluence. The dependence of the ablation rate on the laser fluence has been explained by a model based on plasma absorption. The threshold fluence for complete dissociation of the surface has been determined and is found equal to 0.7 J/cm². Above this threshold, a steady-state target surface condition is obtained within 30 pulses. Below the threshold fluence, CoO nuclei form, which have a pronounced effect on the target composition and morphology. In addition, ellipsometric and reflectance spectra have been measured in the photon energy range of 1.8 to 5.0 eV.     

转镜式高速扫描相机时间分辨率的测定

 介绍了产生时间分辨率的原因，测量时间分辨率在高速摄影中的作用，前人曾做过的工作，时间分辨率测定的难点；着重介绍了新的测量方法，给出了实际测定的结果。结果表明，对于GSJ型相机，时间分辨率可达8.6 ns，测量的均方根误差为1.1 ns。     

Structural study and magnetoresistance effect of epitaxial La0.67Sr0.33MnO3–δ and Pr0.7Ca0.3MnO3−δ multilayer films

La_0.67Sr_0.33MnO_3−δ (LSMO) and Pr_0.7Ca_0.3MnO_3−δ (PCMO) multilayer epitaxial films, which were fabricated with different LSMO and PCMO layer thickness on LaAlO₃ single crystal substrates of (0 0 1) orientation by a direct current magnetron sputtering technique, were studied further, after the structure, magnetoresistance effect and magnetic properties of LSMO/PCMO/LSMO (LPL) trilayer epitaxial films were systemically studied. The superlattice structures of multilayer films were observed according to the diffraction peaks of X-ray diffraction patterns at small angles. The metal–insulator transition temperature (T_P) and peak resistivity (ρ_max) obviously changed when we altered the thickness of PCMO middle layer and the intra-field related with the thickness of those layers and their interaction. Considering the effect of the distribution of electrical field and current, and the interaction among the layers of LSMO and PCMO, an effective fact n* was introduced to replace n (the number of layer). All the calculated values of ρ (the resistivity of multilayer films) accorded with the experimental values.     

Low-temperature transport properties of chemical solution deposited polycrystalline La0.7Sr0.3MnO3 ferromagnetic films under a magnetic field

Polycrystalline La_0.7Sr_0.3MnO₃ (LSMO) films were prepared on SiO₂/Si (001) substrates by chemical solution deposition technique. Electrical and magnetic properties of LSMO were investigated. A minimum phenomenon in resistivity is found at the low temperature (<50 K) under magnetic fields from 0 T to 3 T. Kondo-like spin dependent scattering, which includes both spin polarization and grain boundary tunneling, was observed in the low-temperature electrical transport for the LSMO polycrystalline films. The temperature-dependent resistivity at low temperatures can be well fitted in the framework of elastic scattering, electron-electron (e-e) interaction, Kondo-like spin dependent scattering, and electron-phonon (e-ph) interaction.     

不同生长方向的La0.7Sr0.3MnO3薄膜结构及性能研究

利用磁控溅射方法,在(100),(110)和(111)LaAlO3(LAO)衬底上制备得到了不同生长方向的La0.7Sr0.3MnO3(LSMO)薄膜并对其结构及磁电学性能进行了系统研究.结果表明:LSMO薄膜完全按LAO衬底取向生长;(111)生长方向的薄膜由于晶格畸变程度最小,磁畴方向能较好的保持一致性,从而具有最大的磁饱和强度值;高的磁有序度减弱了巡游电子eg的自旋无序相关散射,有效降低了电阻.但外加磁场后电阻变化不明显,最大磁电阻值只有5.1%.     

Ultrasonic Study on Jahn-Teller Distortions in La1=3Sr2=3CoO3

系统研究了La1=3Sr2=3CoO3单相多晶样品在低温下的电磁输运性质和超声特性．电阻率测量表明,La1=3Sr2=3CoO3在整个温区内都表现出金属特性,并且在235 K处电阻率-温度曲线的斜率发生了变化,同时伴随着铁磁相变．超声声速在铁磁相变温度以下出现软化,并在120 K附近达到最小,之后,随着温度的进一步降低,声速开始硬化,同时出现了一个宽大的超声衰减峰．分析认为,该超声异常可能起源于中等自旋态Co3+的Jahn-Teller效应．