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Guo Y.Y.,Nanjing University of Posts and Telecommunications | Liu J.-M.,Nanjing University | Guo Y.F.,Nanjing University of Posts and Telecommunications | Wei T.,Civil Aviation University of China | And 2 more authors.
AIP Advances | Year: 2015

Our experiments on ferroelectric aging phenomena of a series of acceptor-doped BaTiO3 ceramics demonstrate that after well-aging, all samples show a similar double hysteresis loop under smaller applied electric field, regardless of ionic radius or ionic valence of the acceptor. However, with increasing the applied electric field, the completely constricted loops gradually start to open, indicating the aging effect becomes weak under larger electric field. The unified microscopic mechanism responsible for the similar aging behavior in different acceptor-doped BaTiO3 ceramics may be that the larger field is considered to kinetically facilitate a part of oxygen vacancies short-range hopping. As a result, the defect dipole field provided by oxygen vacancies and the associated defect dipoles frozen in the original states decreases, thus contributing to the weaker aging effect. © 2015 Author(s).

Zhang N.,Henan Normal University | Zhang N.,Henan Province Key Laboratory of Photovoltaic Materials | Su J.,Henan Normal University | Su J.,Henan Province Key Laboratory of Photovoltaic Materials | And 9 more authors.
Journal of Applied Physics | Year: 2014

We investigate the room temperature microstructure and high temperature magnetic properties of Ca2+-substituted Bi1-xCa xFeO3 (0 ≤ x ≤ 0.2) ceramics. The Bi 1-xCaxFeO3 compound transforms from rhombohedral into tetragonal structure with the phase boundary lying around x = 0.1. Based on this, the magnetic modulation becomes significant and the strongest remnant magnetization Mr is obtained at x = 0.1 compound. An important observation is the ferromagnetic-like phase transition revealed at TFM = 878 K in pure BiFeO3. The TFM of Bi 1-xCaxFeO3 varies with Ca concentration and is close to the TAFM when x = 0.1. The convergence between T FM and TAFM implies the severe competition between Fe 3+-O2--Fe3+ and unbalanced Fe 3+-O2--Fe2+ antiferromagnetic exchange interactions, which leads to the dramatic change around TAFM in the M-T curve of x = 0.1 compound. The structure-related modulation of magnetic structure and complex interaction between Fe3+ and Fe2+ may be the driving force for the excellent magnetic properties of x = 0.1 sample. © 2014 AIP Publishing LLC.

Hu Y.-C.,Henan Normal University | Hu Y.-C.,Henan Province Key Laboratory of Photovoltaic Materials | Cui Y.-W.,Henan Normal University | Cui Y.-W.,Henan Province Key Laboratory of Photovoltaic Materials | And 4 more authors.
Chinese Physics Letters | Year: 2016

A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMoO6 (SFMO). X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9(2)% from 94.2(3)%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 μB at 300 K, and the one for the traditional sol-gel method sample is 0.946 μB. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatme is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO. © 2016 Chinese Physical Society and IOP Publishing Ltd.

Shang S.,Henan Normal University | Shang S.,Henan Province Key Laboratory of Photovoltaic Materials | Song G.,Henan Normal University | Song G.,Henan Province Key Laboratory of Photovoltaic Materials | And 4 more authors.
Composites Science and Technology | Year: 2014

The conductive composites of silicone filled with nickel were prepared, with a low percolation threshold of around 35vol%. AC and DC conductivity of nickel/silicone composites with the filler content below or around percolation threshold were studied under uniaxial pressure. A pressure-induced percolation appeared at a very low pressure of finger-sensitive range (0.1-0.7MPa) for each DC conductivity curve. The linear dependence of log σDC on p-1/3 at selected pressures proved the existence of tunneling mechanism and the potential barrier height for electron hopping in metal/polymer composite is strongly pressure dependent. The AC conductivity and the dielectric permittivity of the composite under different uniaxial pressures satisfies the universal dynamic power law, σAC∝ωx, e{open}∝ω-y, respectively. The critical exponents show that the frequency dependence of AC conductivity and dielectric permittivity of metal/polymer composite under various pressures could be well described by polarization effects. © 2014 Elsevier Ltd.

Chang F.,Henan Normal University | Chang F.,Henan Province Key Laboratory of Photovoltaic Materials | Sun Z.,Henan Normal University | Sun Z.,Henan Province Key Laboratory of Photovoltaic Materials | And 6 more authors.
Fuhe Cailiao Xuebao/Acta Materiae Compositae Sinica | Year: 2011

Ni/silicone rubber composites with nickel powders of different particle sizes were prepared at a filler/silicone rubber mass ratio of 2.4:1.0. The piezoresistivity and the dielectric properties of the composite samples at room temperature were measured. The mechanism of electric conduction is discussed together with the SEM images of the samples. The results show that piezoresistivity of Ni/silicone rubber composite is enhanced by reducing the filler particle size: at low pressures, the pressure derivative of resistivity, of samples prepared with Ni powders of particle size 74, 48 and 18 μm is 1.73×104, 2.59×104 and 3.71×104 Ω·m/kPa respectively. The sharp drop in resistivity shifts to the low pressure end as the filler particle size decreases, suggesting that the percolation threshold of Ni/silicone rubber composites decreases with reduced filler particle size. AC conductivity, dielectric constant and dielectric loss of Ni/silicone rubber composites all increase with the decrease of particle size: the conductivity of the sample with filler particle diameter 18 μm reaches about 10-2 S·m-1, which is five orders of magnitude greater than that of the sample with filler particle diameter 74 μm(about 10-7 S·m-1), and the corresponding dielectric constant is also increased from about 102 to about 103. Elasticity, piezoresistivity, and electronic transport properties of the composite can be adjusted by changing the filler particle size.

Hu Y.C.,Henan Normal University | Hu Y.C.,Henan Province Key Laboratory of Photovoltaic Materials | Wang H.Y.,Henan Normal University | Wang H.Y.,Henan Province Key Laboratory of Photovoltaic Materials | And 12 more authors.
Journal of Alloys and Compounds | Year: 2015

Ordered double-perovskite oxides of Sr2- xKxFeMoO6 (0.00 ≤ x ≤ 0.10) are synthesized via sol-gel method. X-ray powder diffraction analysis shows that all the samples have a single phase and exhibit I4/m symmetry. The cation order of Sr2- xKxFeMoO6 decreases from 94.4(2)% to 50.4(2)%, indicating that Fe/Mo is in nearly complete disorder. The magnetic property of Sr2- xKxFeMoO6 samples depends on temperature under zero-field-cooling (ZFC) and field-cooling (FC) processes at an applied magnetic field of 100 Oe. The thermal irreversibility behavior in the FC and ZFC curves indicates a typical cluster glass behavior in this system. The H/M versus M2 curves indicate a second-order magnetic transition, resulting in a small variation in magnetic entropy. Antisite defect is the primary reason for the effective paramagnetic moment. © 2014 Elsevier B.V. All rights reserved.

Hu Y.-C.,Henan Normal University | Hu Y.-C.,Henan Province Key Laboratory of Photovoltaic Materials | Wang Y.-W.,Xinxiang Medical University | Zhang K.-L.,Henan Normal University | And 3 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2012

Samples of Sr2-xKxFeMoO6 (x = 0, 0.01, 0.02, 0.03, 0.04) are prepared by standard solid-state reaction. The crystal structures and magnetic properties for the ordered double perovskite oxides Sr2-xKxFeMoO6 (0 ≤ x ≤ 0.04) are investigated. X-ray powder diffraction studies reveal that all the samples are of single phase and each of them has a I4/m symmetry. The anti-site defects in double perovskite oxides of Sr2FeMoO6 may be adjusted by alkali metal element of K doping. The unit cell magnetizations at 280 K are 1.12 μB for x = 0.00 and 1.26 μB for x = 0.04. The cation-ordering and the variation of structure parameters play improtant roles in determining the magnetism in the doping system. © 2012 Chinese Physical Society.

Li Y.,Henan Normal University | Liu Z.,Henan Normal University | Liu Z.,Henan Province Key Laboratory of Photovoltaic Materials | Wang T.,Henan Normal University | And 2 more authors.
Materials Letters | Year: 2016

A series of nickel/silicone rubber composites, co-filled with micron nickel and submicron nickel particles, were made in this work. The composites with mass ratio of nickel/silicone rubber under 1.8:1 had a high pressure sensitivity; the conductivity changed 9 orders under a low pressure around 0.096 MPa. To our knowledge, this is the lowest content of fillers reported to date in high sensitive polymer-based composites. Furthermore, the composites show good repeatability of piezoresistivity, indicating attractive application prospect. The gauge factor of the composites was studied and a master curve appeared for the composites with different conductive fillers. It showed that the gauge factor of the composites was strain-controlled. © 2016 Elsevier B.V. All rights reserved.

Shang S.,Henan Normal University | Shang S.,Henan Province Key Laboratory of Photovoltaic Materials | Zhou X.,Henan Normal University | Zhou X.,Henan Province Key Laboratory of Photovoltaic Materials | And 3 more authors.
Applied Physics Letters | Year: 2012

In this work, the critical pressure-induced electrical properties of metal/polymer composites were studied systematically. The conductivity and dielectric constant satisfied the scaling electric equations: σ AC ω x and ω - y, respectively. The critical exponents x = 0.72 ± 0.006 and y = 0.32 ± 0.027 agreed with the general relation x + y = 1. The results proved that the transport properties of conductive polymer composites under pressure could be ascribed to polarization effects. A striking loss peak appeared in the curve of double logarithmic plot of tan δ vs. pressure, indicating that the formation of current network required maximum amount of electric energy during the increase of uniaxal pressure. © 2012 American Institute of Physics.

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