Perovskite (La,Sr)MnO3 with tunable electrical properties by the Sr-doping effect

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).