Qingxuan Yu

Nanostructures for Thermoelectric Applications: Synthesis, Growth Mechanism, and Property Studies

Both heterostructures and hollow nanostructures have been predicted as candidates with excellent thermoelectric performance. In this Research News areticle, recent advances with regard to synthetic strategies, growth mechanisms, and thermoelectric properties of one-dimensional heterostructures (segmented and core/shell) and tubular nanostructures are reported. The thermoelectric property studies of Te/Bi core/shell heterostructured nanowires and Bi(2)Te(3) nanotubes indicate that the Seebeck coefficient and thermal conductivity of these materials can be optimized to improve their thermoelectric performance. In addition, the current issues and future research directions for promising thermoelectric nanostructures will be discussed on the basis of these experimental results.

Ultrafast resistive switching in SrTiO3:Nb single crystal

The resistive switching effect of the SrTiO3:Nb (0.05wt %, 0.5 wt %, and 1 wt % Nb) single crystals contact with Ag and Pt, respectively, was studied by in situ monitoring the voltage drop (Vs) across the samples. For Ag/SrTiO3:Nb junction, the response time is as short as 5 ns, which is two orders of magnitude short than that of the Pt/SrTiO3:Nb junction. The effect of metal electrodes on the response time has been discussed, which is related to the barrier height of the junction.

Structural reconstruction and defects transition in mediating room temperature ferromagnetism in Co-doped ZnO film

Room temperature (RT) ferromagnetism (FM) was achieved in H2/N2 annealed Co-doped ZnO films on silicon substrates and we got annealing temperature, Tan, dependence of saturation magnetization, Ms, which increased and finally reached a maximum as Tan elevated. The curve of Ms versus Tan seems like three steps. Surprisingly, after sequential oxygen annealing, Ms of each annealed film decreased abruptly at first, and then restored to its original order after the second annealing, which may owe to the formation of zinc-blende ZnO during thermal oxidation. This experiment illustrated that room temperature ferromagnetism in Co-doped ZnO films is associated with multiple factors.

Current-voltage characteristics of La2-xSrxCuO4/Nb-doped SrTiO3 heterojunctions

[Li, X. G.] Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Dept Phys, Hefei 230026, Peoples R China. Acad Sinica, Int Ctr Mat Phys, Shenyang 110015, Peoples R China.;Li, XG (reprint author), Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Dept Phys, Hefei 230026, Peoples R China;lixg@ustc.edu.cn

Large Magnetodielectric Effect in (1-X) La2NiMnO6—(X) La2/3Sr1/3MnO3 Composites

A large magnetodielectric effect in (1-x) La2NiMnO6—(x) La2/3Sr1/3MnO3 composites over wide frequency and temperature ranges is reported. The results indicate that variation of dielectric constants with magnetic fields depends non-monotonously on the molar ratio of two compounds and reaches a maximum up to 20% for x = 0.4 at the frequency of 1 MHz and field of 1 kOe at room temperature. The further analyses suggest that this effect is closely related to the magnetoresistance. These findings provide an alternative strategy to achieve a room temperature magnetodielectric response in multiferroic composites, indicating that it is promising for potential applications.

Magnetocapacitance of La1−xCaxMnO3/SrTiO3: Nb junctions with different Ca contents

Manganite-based heterojunctions La1−xCaxMnO3/SrTiO3: Nb (0.5 wt. %) with x = 0.2, 0.3, 0.375, 0.4, 0.5, 0.6, and 0.7 have been fabricated, and the lattice constants of La1−xCaxMnO3 films are experimentally studied. The capacitance characteristics of those junctions under a magnetic field have been investigated. Obvious magnetocapacitance was observed in La0.7Ca0.3MnO3/Nb-SrTiO3 p-n junction near the Curie temperature (TC) of La0.7Ca0.3MnO3 at 0.75 T. The result can be explained by phase separation. This study demonstrates the remarkable tunability of the capacitance for phase separated manganite heterojunctions, which may lead to some potential applications.

In-plane anisotropic vortex pinning and relaxation in a stripe-ordered La1.45Nd0.4Sr0.15CuO4 superconductor

The angular dependence of the ac susceptibility for the magnetic field rotated in the CuO(2) plane of a stripe-ordered La(1.45)Nd(0.4)Sr(0.15)CuO(4) single crystal shows an unusual fourfold symmetry below the superconducting transition temperature (T(c)). The real part of the ac susceptibility reaches its maximum for the magnetic field parallel to the stripes, and the in-plane anisotropy of the susceptibility is enhanced with increasing temperature, which indicates that the anisotropy can be ascribed to the vortex pinning of the fourfold symmetric static stripe phase. The in-plane dc magnetic relaxation rate also shows the fourfold symmetry and proves the existence of the anisotropic vortex pinning effect.

Spin structure transition in La(1.6-x)Nd(0.4)Sr(x)CuO(4) superconductors

The field and temperature dependencies of the spin structures in the normal states of La(1.6-x)Nd(0.4)Sr(x)CuO(4) (x = 0.10, 0.12, and 0.15) single crystals have been studied by measuring the magnetoresistance and susceptibility. A negative magnetoresistance appears just below the spin-ordering temperature for the magnetic fields parallel to the CuO(2) plane, which can be attributed to the spin-flop transition of the special spin structure in the normal state of the system. The anisotropic variations of susceptibilities with temperature for all the three specimens can be described in the framework of the crystal-field theory. The well fitted broad peaks of the in-plane susceptibilities χ(ab) for the specimens suggest that the susceptibilities are dominated by Nd(3+), and thus the spin reorientation of Cu(2+) in the CuO(2) plane can not be observed from the study of the susceptibility.