Multiferroic properties of high Curie temperature Bi6Fe1.4Ni0.6Ti3O18 ceramics

Single phase Aurivillius five-layered Bi6Fe1.4Ni0.6Ti3O18 ceramics were synthesized using conventional solid state reaction at 900 degrees C (BFNT) and 920 degrees C (BFNT-1), respectively. X-ray photoelectron spectroscopy reveals the coexistence of Fe3+ and Fe2+ ions in both BFNT and BFNT-1 ceramics with a higher concentration of Fe2+ ions in BFNT-1 samples. High ferroelectric Curie temperatures of over 800 degrees C are measured in both BFNT and BFNT-1 ceramics. The BFNT ceramics exhibit a promising remanent polarization (2P(r)) of 31.3 mu C cm(-2) under an external field of 309 kV cm(-1) while the BFNT-1 ceramics show a deteriorated 2P(r) of 21.3 mu C cm(-2) under an external field of 270 kV cm(-1). In comparison, the BFNT-1 ceramics exhibit desirable saturated magnetization (2M(s)) and remanent magnetization (2M(r)) of 4.01 emu g(-1) and 0.89 emu g(-1), respectively. High magnetic Curie temperatures of over 500 degrees C are also extrapolated in the M-T curves of the BFNT and BFNT-1 ceramics. A 20 degrees C elevation in sintering temperature leads to the abrupt increase of oxygen vacancies in BFNT-1 samples. The increased concentration of oxygen vacancies and their selective occupation around the ferroelectric domain boundaries bring about an appreciable domain-pinning effect in the BFNT-1 ceramics, which is responsible for the deteriorated ferroelectric behavior in BFNT-1 ceramics. It is confirmed that the increase in divalent magnetic ions plays a crucial role in enhancing the magnetic property and deteriorating the ferroelectric behavior. (C) 2019 The Japan Society of Applied Physics