Electrical conduction and polarization behaviors of low temperature sintered Sr1−xLaxFe12−xCoxO19 (x = 0-0.3) hexaferrites

Electrical conduction and polarization behaviors of the Sr1−xLaxFe12−xCoxO19 (x = 0-0.3) hexaferrites for use in low temperature co-fired ceramics (LTCC) technology were investigated according to their temperature dependence of resistivity and complex dielectric permittivity, as well as the polarization versus electric field (P-E) curves. The direct-current (DC) resistivity from room temperature (RT) to 750 °C is mainly dominated by metallic-conduction mechanism and semi-conduction mechanism, which can be responsible for the single metal-semiconductor (M − S) transition behavior. But the double M − S transitions and conduction relaxation are observed with alternating current (AC) measurement in a frequency range of 1 kHz-10 MHz. These abnormal electrical transport behaviors are suggested to be attributed to the coexistence of conduction electrons with different activation energy. The multi particle polarization behavior is obtained in the ferrites from the variation of real permittivity and dielectric loss with temperature, and the space charge polarization mechanism is found to determine the non-linear relationship of P-E. Furthermore, the La3+-Co2+ substitution exhibits significant effects on the electrical transport and dielectric characteristics for the ferrites. Typically, when the substitution amount increases from 0 to 0.3, the activation energy Ea increases from 0.331 to 1.068 eV, the RT resistivity ρd increases from 2.2 × 109 to 3.7 × 109 Ω cm, and the average value of real permittivity ε′(RT-100 °C) measured at 1 kHz decreases from 4.15 to 2.29.