Microstructure and dielectric properties of ion-doped La0.7Sr0.3MnO3 lossy ceramics at radio frequencies

In this paper, the microstructure and dielectric properties of ion-doped La0.7Sr0.3MnO3 are investigated in detail. The polycrystalline ceramics of La(0.7)Sr(0.3)Mn(1-y)MyO(3) (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 epsilon'(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 sigma'(ac)(f) proportional to (2 pi f)(n), demonstrating that the conductive mechanism is hopping conduction.