Regulating mechanisms of Fe-doping on the structure, dielectric and ferroelectric properties of sodium niobate ceramics

NaNbO 3 - x Fe 2 O 3 bulk ceramics have been synthesized to investigate the effects of low-concentration Fe-doping on the crystal structure, dielectric and ferroelectric properties of NaNbO 3 ceramics. The results demonstrate that Fe element either incorporates interstitially into the crystal lattice or substitutes for Nb element at B-site of NaNbO 3 in the low doping range of x < 0.75 mol%. Interstitial doping of Fe reveals a unique broken-line-shaped P - E hysteresis loop with lower remnant polarization P r . Compared to interstitial doping of Fe atom, the substitution of Fe 3+ ion for Nb 5+ ion can result in more fine and uniform-distributed grains, thereby improving the electrical breakdown strength E b . When the Fe-doping concentration of x ≥ 0.75 mol% exceeding its solid solubility, the precipitation of second phase Fe 2 O 3 at grain boundaries occurs. Then the heterogeneous interfacial polar layers between Fe 2 O 3 and NaNbO 3 are constructed, and the interfacial-charge effect increases the peak value of dielectric constant to 4500 at room temperature and maximal polarization P max up to 43 μC cm −2 . Furthermore, Fe-doping induces the accumulation of space charges around domain walls, thus, those charged domain walls generate negative dielectric constant at their specific resonant frequencies, by coupling with the forced vibration of space charges under alternating electric fields. This study reveals the influencing mechanisms of magnetic element Fe-distribution states on the structure and some physical properties of NaNbO 3 ceramics, providing valuable insights for further design of high-energy-storage NaNbO 3 -based ceramic systems. • A unique broken-line P - E loop in NaNbO 3 -based ceramics. • The critical role of Fe-doping in microstructural evolution dielectric and ferroelectric properties regulation. • A negative dielectric constant promising for high-frequency applications.