(La3+ Mg2+) codoped BiFeO3 nanopowders: Synthesis, characterizations, and giant dielectric relaxations

Abstract

A new strategy to improve the dielectric properties of BiFeO3 is proposed by codoping with La3+ and Mg2+ to control the ceramic microstructure and increase the dielectric permittivity (), respectively. The main phase of BiFeO3 is obtained in nanocrystalline powders of LaxBi1-xFe1-xMgxO3 (x = 0, 0.05 and 0.1), which are prepared by a chemical co-precipitation method. The particle size of the codoped LaxBi1-xFe1-xMgxO3 is smaller than that of the BiFeO3. A dense ceramic microstructure without porosity is obtained by sintering at 800 C for 3 h. The mean grain size of the BiFeO3 ceramics decreases with increasing codoping (La3+Mg2+) concentration. The primary roles of La3+ and Mg2+ are to suppress the grain growth and enhance the densification rate, respectively. At 1 kHz, the  of the LaxBi1-xFe1-xMgxO3 with x = 0.1 increased significantly compared to that of the BiFeO3, while the loss tangent (tan) was lower than that of the BiFeO3. In addition, another role of Mg2+ is to increase the  without any effect on the tan. Two dielectric relaxations are observed in low-frequency (150-250 K) and high-temperature (250-400 K) ranges. An X-ray photoelectron spectroscopy shows that the Fe2+/Fe3+ ration in the codoped LaxBi1-xFe1-xMgxO3 increased compared to that of the BiFeO3, corresponding to the increase in . Thus, a low-temperature dielectric relaxation is attributed to the electron hopping between Fe2+OFe3+. On the other hand, a high-temperature dielectric relaxation is caused by interfacial polarization relaxation.

Keywords

• dielectric permittivity
• dielectric relaxation
• electron hopping
• interfacial polarization