High temperature thermoelectric properties of highly c-axis oriented Bi₂Sr₂Co₂O_y thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3(001).Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m·Ω· cm and 202 μV/K at 980 K,resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples.A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature.The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices.     

Bi2Sr2Co2O8体系中Pb替代及I插层对其结构和物性的影响

自今年3月在NaxCo2O4 Yh2o中发现超导电性以来,具有层状结构的Co系氧化物又受到人们广泛的关注.本文在成功合成具有misfit层状结构Bi2Sr2Co2Oy单相样品的基础上,通过Pb对Bi的部分替代、以及I的插层,成功地使其c轴由1.49nm增至1.87nm,并对其输运性质和磁性质进行了系统研究.结果发现:Pb的部分替代并没有使该体系的电阻-温度关系行为发生显著变化,但在低温下使样品呈现自旋玻璃态行为;I的插入不仅使其c轴长度增加,而且样品变为半导体,并不呈现超导电性,在低温下同样呈现自旋玻璃态行为.同时对Pb替代及I插层效应进行了讨论.     

Bi_2Sr_2CaCu_2O_(8+δ)单晶的钉扎力标度和磁通钉扎机制

测量了 Bi2 Sr2 Ca Cu2 O8+δ单晶不同温度下的磁化曲线。根据 Bean临界态模型得到了不同温度下的钉扎力密度 FP 对磁场的依赖关系 ,发现在不同温度下的钉扎力密度可以标度在同一条曲线上。标度函数和最大钉扎力所对应的磁场与不可逆场 Hirr的比值都表明 Si2 Sr2 Ca Cu2 O8+δ单晶在磁通玻璃态的钉扎机制主要是正常相面钉扎。     

Effect of microstructure on the thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO 3(001) through varying the annealing temperature.With the decrease in the annealing temperature,both the size and c-axis alignment degree of grains in the film decrease as well,leading to an increase in the film resistivity.In addition,the decrease in the annealing temperature also results in a slight increase in the Seebeck coefficient due to the enhanced energy filtering effect of the small-grain film.The nanostructured Bi2Sr2Co2Oy film with an average grain size of about 100 nm shows a power factor comparable to that of films with larger grains.Since the thermal conductivity of the nanostructured films can be depressed due to the enhanced phonon scattering by grain boundary,a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.     

Photoelectric Characteristic of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 p-n Heterojunctions

Good rectifying current-voltage characteristics and nanosecond photoelectric effects are observed in the p-n hereto junctions of La0.9Sr0.1 MnO3/SrNb0.01 Ti0.99O3 fabricated by laser molecular beam epitaxy. The rise time is about 26ns and the full width at half maximum is about 125ns for the open-circuit, photovoltaic pulses when the La0.9Sr0.1MnO3 film in the heterojunction is irradiated by a laser operated at wavelength 308nm with pulse duration of about 25 ns. A qualitative explanation is presented, based on an analysis of the photoelectric effect of p-n hereto junction.     

Rectifying and photovoltaic properties of ZnCo2O4/Si heterostructure grown by pulsed laser deposition

ZnCo2O4/Si heterostructures have been fabricated by a pulsed laser deposition method, and their transport behaviors and photovoltaic properties have been characterized. The ZnCo2O4/Si heterostructures show a good rectifying behavior at five different temperatures ranging from 50 K to 290 K. The measurements of the photovoltaic response reveals that a photovoltage of 33 mV is generated when the heterostructures are illuminated by a 532 nm laser of 250 mW/cm2and mechanically chopped at 2500 Hz. Both the photocurrent and the photovoltage clearly increase with the increase of the laser intensity at room temperature. However, the heterostructures' photovoltage peak decreases with the increase of the temperature. This work may open new perspectives for ZnCo2O4/Si heterostructure-based devices.     

Closing the pseudogap by Zeeman splitting in Bi2Sr2CaCu2O8+y at high magnetic fields.

Interlayer tunneling resistivity is used to probe the low-energy density-of-states (DOS) depletion due to the pseudogap in the normal state of Bi2Sr2CaCu2O8+y. Measurements up to 60 T reveal that a field that restores DOS to its ungapped state shows strikingly different temperature and doping dependencies from the characteristic fields of the superconducting state. The pseudogap closing field and the pseudogap temperature T small star, filled evaluated independently are related through a simple Zeeman energy scaling. These findings indicate a predominant role of spins over the orbital effects in the formation of the pseudogap.     

(Bi,Pb)_2Sr_2CaCu_2O_y单晶的磁通钉扎研究

我们通过对重Pb掺杂的Bi-2212((Bi,Pb)-2212)单晶磁化性质的测量来研究磁通钉扎性能,发现样品中存在与温度有明显依赖关系的鱼尾效应,且此鱼尾效应不仅体现在磁滞洄线上,还体现在不同磁场下零场冷的M～T曲线的交叠上.同时我们采用非线性磁通蠕动模型,并考虑表面位垒和体钉扎的影响,运用数值模拟分析了样品的磁化性质,结果表明(Bi,Pb)-2212单晶的鱼尾效应源于重Pb掺杂导致样品各向异性的降低所引起的强的体钉扎效应,而高温的磁化性质主要取决于表面位垒的作用.     

High critical temperature by resonant quantum confinement: Evidence for polarons ordering at T *≈1.5T c in Bi-2212 and La-214 by EXAFS

Il Nuovo Cimento D - The temperature dependence of local Cu site conformations in single-domain crystals of Bi2Sr2CaCu2O8+y (Bi-2212) and La1.85Sr0.15CuO4 (La-214) has been determined by EXAFS...     

Persistence of strong electron coupling to a narrow boson spectrum in overdoped Bi2Sr2CaCu2O(8+delta) tunneling data

A d-wave, Eliashberg analysis of break-junction and STM tunneling spectra on Bi2Sr2CaCu2O(8+delta) (Bi2212) reveals that the spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in alpha2F(omega). The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk T(c) values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.     

基于低温光声光谱技术的高Tc超导材料Bi2Sr2CaCu2O8

在光声光谱技术基础上,将不同仪器组装成一套系统,并成功测量出碳黑的光声光谱。利用低温检测系统测定高温超导材料Bi2Sr2CaCu2O8在室温和液氮温度下的光声光谱,发现室温时在598nm和695nm有峰值,液氮温度时在466nm出现峰值。以吸收系数近似为1的碳黑为参照,利用归一化方法得到了Bi2Sr2CaCu2O8相对吸收系数谱图,并进行了初步的探讨,得到了该超导材料的一些信息,为利用低温光声光谱技术,研究超导材料的超导特性提供了一种可行的途径。     

Scanning tunneling spectroscopy of Bi(2)Sr(2)CuO(6+delta): new evidence for the common origin of the pseudogap and superconductivity

Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi(2)Sr(2)CuO(6+delta) between 275 mK and 82 K. Below T(c) = 10 K, the spectra show a gap with well-defined coherence peaks at +/-Delta(p) approximately 12 meV, which disappear at T(c). Above T(c), the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T(*) approximately 68 K. The comparison with Bi(2)Sr(2)CaCu(2)O(8+delta) demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin.     

Mechanisms of the pancake vortex and vortex line movement in the high Tc superconductors Bi2Sr2CaCu2O8+δand La1.93Sr0.07CuO4+δ

In the strict sense, it is not very clear why with magnetic field increasing, the normal-superconductive (NS) transition becomes broad for Bi2Sr2CaCu2O8+δ(Bi2212) while the NS transitions are almost parallel for La1.93Sr0.07CuO4+δ(La214). In this paper, R-T relations are measured by the six-probe method. We propose a moving mechanism of the pancake vortex and vortex line for Bi2212. The theoretical curves fit the experiment data well.     

Entanglement of solid vortex matter: a boomerang-shaped reduction forced by disorder in interlayer phase coherence in Bi2Sr2CaCu2O8+y

We present evidence for entangled solid vortex matter in a glassy state in a layered superconductor Bi2Sr2CaCu2O8+y containing randomly splayed linear defects. The interlayer phase coherence--probed by the Josephson plasma resonance--is enhanced at high temperatures, reflecting the recoupling of vortex liquid by the defects. At low temperatures in the vortex solid state, the interlayer coherence follows a boomerang-shaped reentrant temperature path with an unusual low-field decrease in coherence, indicative of meandering vortices. We uncover a distinct temperature scaling between in-plane and out-of-plane critical currents with opposing dependencies on field and time, consistent with the theoretically proposed "splayed-glass" state.     

Resonant spin excitation in an overdoped high temperature superconductor

An inelastic neutron scattering study of overdoped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 83 K) has revealed a resonant spin excitation in the superconducting state. The mode energy is E(res) = 38.0 meV, significantly lower than in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) ( T(c) = 91 K, E(res) = 42.4 meV). This observation, which indicates a constant ratio E(res)/k(B)T(c) approximately 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high temperature superconductors.     

溶胶-凝胶法制备Bi3+,Yb3+单掺和共掺Gd2O3荧光粉及其荧光性能

利用溶胶-凝胶法制备了Bi³⁺、Yb³⁺单掺和共掺的Gd₂O₃荧光粉。研究了Gd_2-x-yO₃: Bi_x³⁺,Yb_y³⁺的制备条件并表征了Gd_2-x-yO₃: Bi_x³⁺,Yb_y³⁺的荧光性能。 由于Gd₂O₃: Bi³⁺,Yb³⁺中Bi³⁺对Yb³⁺的能量传递,Gd₂O₃: Bi³⁺,Yb³⁺在Bi³⁺的特征激发峰338 nm激发时,可以产生Yb³⁺的900~1 100 nm近红外特征发射和Bi³⁺的400~700 nm特征发射的两个波段光谱。所制备的Gd₂O₃: Bi³⁺,Yb³⁺荧光材料可将太阳光谱中硅太阳能电池吸收较弱的300~400 nm光转换成有较强吸收的500~700 nm 和1 000 nm附近的近红外光子,提高硅太阳能电池的光伏效率。     

Temperature-dependent Raman scattering study of cation-deficient Aurivillius phases: Bi2WO6 and Bi2W2O9

Temperature-dependent Raman scattering experiments were performed on Bi(2)WO(6) and Bi(2)W(2)O(9). Significant changes in the phonon properties of Bi(2)WO(6) were observed as the temperature was increased due to decreased distortion from the B2cb structure. It was shown that instability of the 57 cm(-1) mode that behaved as a soft mode under pressure is not responsible for the Pca2(1) to B2cb phase transition taking place in Bi(2)WO(6) at 933 K. This result confirmed that this mode is not related to the [Formula: see text] tilt mode, which disappears upon change in symmetry from Pca2(1) to B2cb. Bi(2)W(2)O(9) does not exhibit any structural phase transition in the 298-800 K range. However, the temperature dependence of Raman bands indicated that the Bi(2)W(2)O(9) structure evolves with decreasing temperature from 800 to 298 K towards a more symmetric structure that was reported above 2.8 GPa at room temperature. This structural change is driven by displacement of the W atoms and is different from that exhibited by Bi(2)WO(6) and other members of the Aurivillius family but similar to that exhibited by WO(3). Our results also show that Bi(2)W(2)O(9) belongs to the small group of compounds that show the presence of low wavenumber modes characterized by unusually small linewidths.     

Sr2Bi4Ti5O18的压致结构相变

 使用4∶1的甲醇-乙醇混合液作传压介质，利用金刚石对顶砧装置（DAC），研究了层状铁电体Sr₂Bi₄Ti₅O₁₈的在位高压拉曼光谱和压致结构相变（0～27 GPa）。发现在8.31 GPa，Sr₂Bi₄Ti₅O₁₈经历了一次结构相交。在23.13 GPa以上，Sr₂Bi₄Ti₅O₁₈似乎出现了压致非晶相交的先兆。并使用内模方法对Sr₂Bi₄Ti₅O₁₈的内模进行了指认。     

Bi3+掺杂对Sr2MgSi2O7∶Eu2+荧光粉的结构及发光性能的影响

采用溶胶-凝胶法在还原气氛下制备了Sr₂MgSi₂O₇∶Eu²⁺,xBi³⁺(x=0,0.02,0.04,0.06,0.08,0.1)荧光粉,并用XRD、TG-DTA及激发与发射谱仪对样品的结构及发光性能进行了表征。结果发现:单掺杂Bi³⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为286 nm的宽带谱,这是由于激发态时Bi³⁺的³P₁→¹S₀电子能级跃迁而造成的;单掺杂Eu²⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为358 nm的宽带谱,这是典型的Eu²⁺的4f⁶5d¹→4f⁷跃迁而引起的。当Bi³⁺离子掺杂到Sr₂MgSi₂O₇∶Eu²⁺样品的摩尔分数为0.04时,样品的发射强度是未掺杂Bi³⁺离子样品的1.9倍。     

Doping controlled superconductor-insulator transition in Bi2Sr2-xLaxCaCu2O8+delta

We show that the doping-controlled superconductor-insulator transition (SIT) in a high critical temperature cuprate system (Bi(2)Sr(2-x)La(x)CaCu(2)O(8+delta)) exhibits a fundamentally different behavior than is expected from conventional SIT. At the critical doping, the sheet resistance seems to diverge in the zero-temperature limit. Above the critical doping, the transport is universally scaled by a two-component conductance model. Below, it continuously evolves from weakly to strongly insulating behavior. The two-component conductance model suggests that a collective electronic phase-separation mechanism may be responsible for this unconventional SIT behavior.