Yiqun Xie

Electric Field-Induced Giant Strain and Photoluminescence-Enhancement Effect in Rare-Earth Modified Lead-Free Piezoelectric Ceramics

In this work, an electric field-induced giant strain response and excellent photoluminescence-enhancement effect was obtained in a rare-earth ion modified lead-free piezoelectric system. Pr(3+)-modified 0.93(Bi0.5Na0.5)TiO3-0.07BaTiO3 ceramics were designed and fabricated by a conventional fabrication process. The ferroelectric, dielectric, piezoelectric, and photoluminescence performances were systematically studied, and a schematic phase diagram was constructed. It was found the Pr(3+) substitution induced a transition from ferroelectric a long-range order structure to a relaxor pseudocubic phase with short-range coherence structure. Around a critical composition of 0.8 mol % Pr(3+), a giant reversible strain of ∼0.43% with a normalized strain Smax/Emax of up to 770 pm/V was obtained at ∼5 kV/mm. Furthermore, the in situ electric field enhanced the photoluminescence intensity by ∼40% in the proposed system. These findings have great potential for actuator and multifunctional device applications, which may also open up a range of new applications.

Sandwiched nanoarchitecture of reduced graphene oxide/ZnO nanorods/reduced graphene oxide on flexible PET substrate for supercapacitor

Reduced graphene oxide (rGO)/zinc oxide (ZnO) nanorods/rGO sandwich is fabricated on chemical vapor deposition graphene film/polyethylene therephthalate substrate for flexible supercapacitor electrodes. Studies show that ZnO nanorods in the electrodes prevent aggregation of rGO sheets and help forming a porous structure. Specific capacitance of 51.6 F/g at the scan rate of 10 mV/s is achieved for the rGO/ZnO nanorods/rGO sandwich, showing that such composite is promising for application in flexible supercapacitors.

Conductance and spin-filter effects of oxygen-incorporated Au, Cu, and Fe single-atom chains

We studied the spin-polarized electron transport in oxygen-incorporated Au, Cu, and Fe single-atom chains (SACs) by first-principles calculations. We first investigated the mechanism responsible for the low conductance (<1G0) of the Au and Cu SACs in an oxygen environment reported in recent experiments. We found that for the Au SACs, the low conductance plateau around 0.6G0 can be attributed to a distorted chain doped with a single oxygen atom, while the 0.1G0 conductance comes from a linear chain incorporated with an oxygen molecule and is caused by an antibonding state formed by oxygens occupied frontier orbital with dz orbitals of adjacent Au atoms. For the Cu SACs, the conductance about 0.3G0 is ascribed to a special configuration that contains Cu and O atoms in an alternating sequence. This exhibits an even-odd conductance oscillation with an amplitude of ∼0.1G0. In contrast, for the alternating Fe-O SACs, conductance overall decreases with an increase in O atoms and it approaches nearly zero for th...

Melting of icosahedral nickel clusters under hydrostatic pressure.

The thermal stabilities and melting behavior of icosahedral nickel clusters under hydrostatic pressure have been studied by constant‐pressure molecular dynamics simulation. The potential energy and Lindemann index are calculated. The overall melting temperature exhibits a strong dependence on pressure. The Lindemann index of solid structure before melting varies slowly and is almost independent of pressure. However, after the clusters melt completely, the Lindemann index at the overall melting point strongly depends on pressure. The overall melting temperature is found to be increasing nonlinearly with increasing pressure, while the volume change during melting decreases linearly with increasing pressure. Under a high pressure and temperature environment, similar angular distributions were found between liquid and solid structures, indicating the existence of a converging local structure.

Reduced Graphene Oxide-ZnO Nanocomposites for Flexible Supercapacitors

In this paper, we present a novel nanostructure of reduced graphene oxide supported by vertical aligned ZnO nanorods for flexible supercapacitors. Layer-by-layer strategies are adopted to fabricate the electrodes on PET flexible substrates. Cu foil, Al-doped ZnO film and chemical-vapor deposition graphene is introduced on PET to serve as current collectors. ZnO nanorods are synthesized by a hydrothermal method under low temperature. The structural and electrochemical properties of these nanostructured electrodes are systematically investigated.

Novel mechanical behaviors of wurtzite CdSe nanowires

As an important semiconducting nanomaterial, CdSe nanowires have attracted much attention. Although many studies have been conducted in the electronic and optical properties of CdSe NWs, the mechanical properties of Wurtzite (WZ) CdSe nanowires remain unclear. Using molecular dynamics simulations, we have studied the tensile mechanical properties and behaviors of [0001]-oriented Wurtzite CdSe nanowires. By monitoring the stretching processes of CdSe nanowires, three distinct structures are found: the WZ wire, a body-centered tetragonal structure with four-atom rings (denoted as BCT-4), and a structure that consists of ten-atom rings with two four-atom rings (denoted as TAR-4) which is observed for the first time. Not only the elastic tensile characteristics are highly reversible under unloading, but a reverse transition between TAR-4 and BCT-4 is also observed. The stretching processes also have a strong dependence on temperature. A tubular structure similar to carbon nanotubes is observed at 150xa0K, a single-atom chain is formed at 300, 350 and 450xa0K, and a double-atom chain is found at 600xa0K. Our findings on tensile mechanical properties of WZ CdSe nanowires does not only provide inspiration to future study on other properties of CdSe nanomaterials but also help design and build efficient nanoscale devices.

Conductance of single-atom magnetic junctions: A first-principles study

We present a first-principles investigation to show that the contact conductance of a half conductance quantum (G0/2) found previously does not generally hold for single-atom magnetic junctions composed of a tip and an adatom adsorbed on a surface. The contact conductance of the Ni-Co/Co(111) junction is approximately G0/2, while for the Co-Co/Co(111), Ni-Ni/Ni(111), and Ni-Ni/Ni(001) junctions the contact conductances are 0.80G0,u20091.55G0, and 1.77G0, respectively. The deviation from G0/2 is mainly caused by the variation of the spin-down conductance largely determined by the minority d orbitals, as the spin-up one changes little for different junctions.

Origin of the smaller conductances of Rh, Pb, and Co atomic junctions in hydrogen environment

We study theoretically the structural and electronic origins of the smaller conductances (one conductance quantum, G0, and smaller) of Rh, Pb, and Co metal atomic junctions (MAJs) in a hydrogen environment, as were measured in recent experiments. For the Rh MAJs, the 1G0 conductance is attributed to a stable contact bridged by a single hydrogen molecule whose antibonding state provides a single transport channel. For the Pb and Co MAJs the 1G0 conductance is, however, ascribed to a linear atomic chain adsorbing two dissociated H atoms, which largely reduces the density of states at the Fermi energy with respect to the pure ones. On the other hand, the small conductances of 0.3G0 (Rh) and 0.2G0 (Co) are due to H-decorated atomic chains connected to electrodes by a H atom.

Theoretical studies of the lithium atom on the silicon carbide nanotubes

Based on density functional theory method, we have investigated structural, electronic, and magnetic properties of lithium (Li) atom adsorbed on silicon carbide (SiC) zigzag (9,0) and armchair (5,5) nanotubes. Effective adsorptions are found on both inner- and outer-side of the SiC nanotubes, with adsorption energies ranging from 1.03 to 1.71xa0eV. Interestingly, we have found that SiC nanotubes exhibit different behaviors with several Li adsorption sites. Li adsorptions on the s-Si and s-H sites of the outer surface and all the five sites of the inner surface in zigzag (9,0) nanotube emerge metallic features, whereas adsorptions on other sides of (9,0) and all sites of armchair (5,5) SiC nanotubes show semiconducting characters. The calculating results also indicate that lithium adsorptions on most sites of SiC nanotubes yield spontaneous magnetization, where net magnetic moment is 1xa0μB. Additionally, spin density of states, spin density distribution, and charge density difference are also calculated to investigate the electronic and magnetic properties of SiC nanotubes induced by Li adsorption.

Conductance of ferro- and antiferro-magnetic single-atom contacts: A first-principles study

We present a first-principles study on the spin dependent conductance of five single-atom magnetic junctions consisting of a magnetic tip and an adatom adsorbed on a magnetic surface, i.e., the Co-Co/Co(001) and Ni-X/Ni(001) (X = Fe, Co, Ni, Cu) junctions. When their spin configuration changes from ferromagnetism to anti-ferromagnetism, the spin-up conductance increases while the spin-down one decreases. For the junctions with a magnetic adatom, there is nearly no spin valve effect as the decreased spin-down conductance counteracts the increased spin-up one. For the junction with a nonmagnetic adatom (Ni-Cu/Ni(001)), a spin valve effect is obtained with a variation of 22% in the total conductance. In addition, the change in spin configuration enhances the spin filter effect for the Ni-Fe/Ni(001) junction but suppresses it for the other junctions.