Yunxia Gao

Surface chemical composition and optical properties of nitrogen-doped Ba0.6Sr0.4TiO3 thin films

The effect of nitrogen (N) doping on surface chemical composition and optical properties of Ba0.6Sr0.4TiO3 (BST) thin films have been investigated using x-ray photoemission spectroscopy (XPS) and transmittance measurement. It was found that the nitrogen doping induced Ti3+∕4+ states and formed Ti–N bonds in BST films. With lower implantation energy, the oxygen vacancies can be effectively eliminated because of N dopants substitution. Unfortunately, the oxygen vacancies possibly increased when enhance implantation energy. In addition, the N-doped BST films indicated larger amount of perovskite phase and lower content additional phase at surface. The chemical shifts in XPS confirmed the forming of Ba–N and Sr–N bonds in N-doped BST films. The optical properties for as-grown and N-doped BST films were considered at wavelength range from 190to1100nm. The optical constants, including refractive index n and extinction coefficient k, were calculated by fitting transmittance spectra with single Tauc-Lorenz and Lo...

Electrical properties of garnet-like lithium ionic conductors Li5+xSrxLa3−xBi2O12 fabricated by spark plasma sintering method

A typical approach involving Pechini method and spark plasma sintering (SPS) method was presented for the preparation of high density Li5+xSrxLa3−xBi2O12 (x = 0, 1) ceramics. Phase formation, microstructure, grain size and electrical properties of the specimens were examined using XRD, SEM and alternating current impedance spectroscopy (ACIS). Dense Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics with pure garnet-like phase, relative density of 97% and average grain size of about 5 μm were fabricated using this approach. The total conductivities at 298 K of Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics prepared by the SPS method are 5.1×10−5 and 6.8×10−5 S/cm, respectively, 2 times higher than that of samples prepared by the conventional sintering method.

L10 FePt nanoparticles with distinct perpendicular magnetic anisotropy prepared on Au buffer layers by a micellar method

FePt nanoparticles were self-assembled on a MgO (001) substrate by a micellar method. We introduced an Au buffer layer to control the lattice orientation and the magnetic alignment of FePt nanoparticles. A distinct c-axis preferred orientation of the FePt nanoparticles was achieved during the thermal annealing treatment. The driving force of lattice reorientation is considered to be the result of the stress caused by the lattice misfit between Au and FePt. The degree of c-axis orientation is significantly enhanced with increasing Au thickness, which is attributed to the decrease of the in-plane lattice and the improved crystal quality of the Au layer. Perpendicular magnetic anisotropy was observed for the FePt samples with the Au buffer layer. The out-of-plane coercivity and remanence ratio are 3.1 kOe and 0.8, respectively, which far exceed the in-plane values.

Magnetic properties of Sm2(Fe1−xGax)17 compounds (x = 0–0.5)

Abstract Sm 2 (Fe 1− x Ga x ) 17 ( x = 0–0.5) compounds were prepared by arc melting. X-ray diffraction patterns showed that all compounds were single phase with rhombohedral Th 2 Zn 17 -type structure. X-ray diffraction patterns of the aligned samples showed that the alloys with x = 0.15, 0.20 and 0.25 have uniaxial anisotropy at room temperature. The spin reorientation transition temperatures were measured by a superconducting quantum interference device (SQUID) and a magnetic balance. A tentative phase diagram was constructed. The substitution of Ga for Fe leads to an increase in the reorientation temperature and the lattice constants. The Curie temperature increases with the Ga concentration, and achieves a maximum at x = 0.2, then decreases. The saturation magnetization decreases monotonically with Ga concentration. The coupling constants A TT and A RT were derived using a mean molecular field model. A TT reaches a maximum at x = 0.3 and then decreases with x , but A RT is almost unchanged with varying x .

Evolution of multiple dielectric responses and relaxor-like behaviors in pure and nitrogen-ion-implanted (Ba, Sr)TiO3 thin films

Multiple dielectric responses are comparatively investigated in the pure and nitrogen-ion-implanted (Ba, Sr)TiO3 (BST) films. Larger diffusive degree of phase transition and more relaxor-like features than those of pure BST films are observed in implanted ones, where the long-range-dipolar-correlated-orders were further segregated into local polar orders after the implantation. Moreover, the implanted films possess a transition from local reorientations of groups of dipoles induced nearly constant-loss (NCL) type to oxygen vacancies (Vo) hopping type conduction at high temperature. Whereas, pure films behave as NCL type conduction along with a dielectric relaxation, which arises from the motions of defect complexes Vo 2+–Ti3+.

Magnetic properties of (Er,R)2Fe17Ny compounds (R=Y,Gd)

Structural and magnetic properties of the interstitial (Er1−xRx)2Fe17Ny compounds with R=Y and Gd, x=0, 0.1, 0.25, 0.4, 0.5, 0.6, 0.75, and 1.0, 2<y<3, have been investigated. All the parent compounds crystallize in the Th2Ni17‐type structure, except for Gd2Fe17 which crystallizes in the Th2Zn17‐structure. All nitrides preserve the same structure as the parents. Introduction of nitrogen results in an increase in lattice constants a and c, and the expansion of unit‐cell volume is about 6%. The Curie temperature was found to increase distinctly after nitrogenation. Nitrogen absorption leads to an increase in saturation magnetization, the values of the saturation magnetization increase monotonically with increasing Y or Gd concentration. Nitrogenation increases the uniaxial anisotropy of the Er sublattice, and causes a spin reorientation. The Y and Gd concentration dependencies of the spin reorientation temperature Tsr exhibit maxima. The tentative spin phase diagrams are presented.

Enhanced micro-vibration sensitive high-damping capacity and mechanical strength achieved in Al matrix composites reinforced with garnet-like lithium electrolyte

A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li7-xLa3Zr2-xNbxO12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment.

Preparation and enhancement of ionic conductivity in Al-added garnet-like Li6.8La3Zr1.8Bi0.2O12 lithium ionic electrolyte

Garnet-like Li6.8La3Zr1.8Bi0.2O12 (LLZBO) + x mol.% Al2O3 (x = 0, 1.25, 2.50) lithium ionic electrolytes were prepared by conventional solid state reaction method under two different sintering temperatures of 1000°C and 1100°C. XPS, induced coupled plasma optical emission spectrometer (ICP-OES), XRD and AC impedance spectroscopy were applied to investigate the bismuth valance, lithium concentration, phase structure and lithium ionic conductivity, respectively. Electrical measurement demonstrated that ionic conductivity of Al-added LLZBO compounds could be obviously improved when the sample sintering temperature increased from 1000°C to 1100°C. The highest ionic conductivity 6.3×10-5 S/cm was obtained in the LLZBO-1.25%Al sample sintered at 1100°C, in consistent with the lowest activation energy 0.45 eV for the lithium ion migration. The mechanism related with good ionic conductivity in the Al-added LLZBO sample was attributed to the lattice distortion induced by the partial Al substitution at Zr sites, which is helpful to improve the migration ability of Li ions in lattice.

Study on high performance Sm2Fe17Nx magnets

In this paper, the remanence properties of Co-Sn, Co-Ti and CO-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-gamma-Fe2O3 samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-gamma-Fe2O3 samples. It is the small MRD, SFD(r), IRS and large DH(r) of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording.

Electron injection of SrTiO3∕Si interfacial layer

The electrical properties of the SrTiO3(STO)∕Si interfacial layer were studied by measuring STO metal-insulator-semiconductor (MIS) structure. The C-V measurements showed that there existed electron injection at the STO/Si interface under the higher sweep voltages. The electron injection behavior was analyzed and discussed in detail. By analyzing the voltage distribution of the semiconductor Si, the insulator STO, and the STO/Si interfacial layer in MIS structure, the electron injection electric field of interfacial layer was estimated to be about 5.5MV∕cm.