We report a comprehensive understanding of the dielectric, ferroelectric, and electrical transport properties of BaFe 12 O 19 , a typical M-type hexaferrite, over a wide temperature (123–523 K) and frequency (1 Hz–20 MHz) range. The analysis of ac conductivity, complex impedance, electric modulus and relative dielectric permittivity spectra indicated that both dipolar polarization and electronic charge transport contributed to the electrical response. The temperature evolution of electrical transport reveals successive changes in conduction mechanism, reflecting transitions of electrical conductivity between metallic-like state and semiconductor state associated with reorganization of the contributions from grain and grain-boundary in the sample depending on the range of temperature and applied ac field frequency. At low temperatures, the freezing of electric dipoles corresponds to a quantum-paraelectric state and nearly constant loss behaviour, while intermediate temperatures showed frustrated ferroelectric and relaxor state due to the competition between dipolar contribution and electronic conductivity. A phase boundary between the dipolar polarization and electronic conduction has been established, which shifts to higher temperature at higher applied frequency. A stable ferroelectric state has been indicated at higher temperatures and frequencies. The material showed a reasonably strong magneto-electric response at room temperature with magneto-electric coupling coefficient in the range of 7 – 17 mV cm −1 Oe −1 . • BaFe 12 O 19 was studied across a broad temperature (123–523 K) and frequency (1 Hz–20 MHz) range, revealing detailed ac conductivity and dielectric responses correlated with its ferroelectric and magneto-electric behavior. • Impedance and electric modulus analyses highlight the distinct roles of grains and grain boundaries in charge relaxation and conduction processes. • A phase evolution from super-paraelectric to stable ferroelectric states was observed, governed by dipolar reorientation and space-charge polarization effects. • BaFe 12 O 19 exhibits high energy storage efficiency at low temperature quantum paraelectric state. • The identified frequency–temperature boundary between polarization and electronic conduction supports the design of tunable dielectric and magneto-electric materials for energy harvesting and conversion applications.
Kishor et al. (Fri,) studied this question.