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Yan K.-L.,Shandong University | Fan R.-H.,Shandong University | Wang X.-A.,Shandong University | Chen M.,Shandong University | And 6 more authors.
RSC Advances | Year: 2014

In this paper, the microstructure and dielectric properties of ion-doped La0.7Sr0.3MnO3 are investigated in detail. The polycrystalline ceramics of La0.7Sr0.3Mn 1-yMyO3 (M = Fe, Ni, Cu; y = 0.3 or 0.5) are prepared by the sol-gel/sintering method. The symmetry of the crystal structure is improved and the dielectric properties obtained in the frequency range from 80 MHz to 1 GHz can be tuned by the doping of Fe, Ni, and Cu ions. With regard to the dielectric properties in lossy ceramics, the decrease of real permittivity ε′r for the doping of Fe and Ni will be effective for impedance-matching; the enhanced dielectric losses in the Ni and Cu doping samples will promote stronger absorption. Thus, the improved dielectric properties make ion-doped La0.7Sr0.3MnO3 promising candidates for lossy ceramics in microwave electronics. In addition, the experimental results of permittivity were checked by K-K relations, and the frequency dispersion behaviors of the conductivity within a certain frequency range accord with the Jonscher's power law in the form of σ′ac(f) ∝ (2πf)n, demonstrating that the conductive mechanism is hopping conduction. © the Partner Organisations 2014.

Yan K.-L.,Shandong University | Fan R.-H.,Shandong University | Chen M.,Shandong University | Sun K.,Shandong University | And 4 more authors.
Journal of Alloys and Compounds | Year: 2015

Recently, the negative index materials (NIMs), also called double negative materials (DNMs) are receiving an increasing attention due to their many unique electromagnetic properties and attractive applications prospect. DNMs are now well established in "artificial" metamaterials, but it remains a challenge from the perspective of "natural" materials, especially in single phase materials. Herein, the La1- xSrxMnO3 (LSMO, x = 0.1, 0.2, 0.3, 0.4, 0.5) ceramics with different Sr mole ratio (x) were prepared by combining the sol-gel process with auto-combustion, followed by cold-pressing and sintering. The dielectric properties of LSMO were studied at frequency ranges from 104 Hz to 108 Hz. The negative permittivity was realized, and the permittivity and ac conductivity were drastically tuned by the Sr-doping effect. Experimental results and theoretical simulation results indicate that the negative permittivity is attributed to the Lorentz resonance (x = 0.1) and the plasma oscillation (x > 0.1), respectively. It is further found that the doping elements tune the permittivity by adjusting the concentration of the effective electrons, which is further supported by the frequency dependences of the conductivity (σ′ac-f). © 2014 Elsevier B.V. All rights reserved.

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