Dual-relaxation-induced tunable colossal dielectric behavior of doped (Ca0.6Sr0.4)1.15Tb1.85Fe2O7 ceramics

Abstract Dielectric characteristics of (1– x )(Ca 0.6 Sr 0.4 ) 1.15 Tb 1.85 Fe 2 O 7 - x Ca 3 Mn 2 O 7 ( x = 0, 0.1, 0.15; abbreviated as 0-CMO, 0.1-CMO, and 0.15-CMO, respectively) ceramics were investigated over a range of temperatures and frequencies. Both 0.1-CMO and 0.15-CMO samples exhibit two adjacent “step-like” dielectric abnormities in the temperature range from −150 to 150 °C; in contrast, 0-CMO exhibits only one dielectric abnormity in the temperature range. Due to the two “jumps”, the two samples exhibit one to two orders of magnitude larger dielectric constants and much wider dielectric plateaus than those of 0-CMO, which may be mainly attributed to the dual-relaxation mechanism caused by the introduction of Mn 2+ /Mn 3+ /Mn 4+ mixed-valent structure besides the Fe 2+ /Fe 3+ one. We found that the steepness of the dielectric step, wideness of dielectric plateaus, and values of the relative dielectric constants could be controlled by introducing the CMO-dopant. Among all the prepared samples, 0.1-CMO exhibits the highest relative dielectric constant and the widest plateau ( e r ′ > 1.7×10 5 at 1 kHz from 16 °C to 311 °C).