Room-Temperature Ferromagnetism in Nickel-Doped Wide Band Gap Ferroelectric Bi_0.5K_0.5TiO₃ Nanocrystals

Abstract

We report the effect of nickel doping on the structural, optical, and magnetic properties of Bi 0.5 K 0.5 TiO 3 nanocrystal. The X-ray diffraction results indicated that Ni was substituted into the Ti sites in Bi 0.5 K 0.5 TiO 3 and the NiTiO 3 phase was formed when Ni concentration was higher than 3 mol%. The band gap value decreased from 3.31 eV to 2.96 eV when the Ni concentration changed from 0 to 3 mol% and then increased with higher Ni concentration. Both weak-ferromagnetism and diamagnetism coexisted in un-doped Bi 0.5 K 0.5 TiO 3 samples. The ferromagnetic signal strongly influenced the paramagnetic signal for Ni-doped Bi 0.5 K 0.5 TiO 3 samples at room temperature. The room-temperature ferromagnetism in Ni-doped Bi 0.5 K 0.5 TiO 3 samples could be contributed by intrinsic reason due to presence of Ni ion in Bi 0.5 K 0.5 TiO 3 crystal and by extrinsic reason due to segregation of NiTiO 3 clusters when Ni concentration was over 3 mol% threshold. This method may provide a useful way to get both single-phase multiferroics and composite multiferroics materials.

EFFECTS OF Co DOPING ON PROPERTIES OF ILMENITE NiTiO3 CERAMICS

“…The modification optical band gap of NiTiO 3 materials was recently reported for metal (Ag-, Mo-) or non-metal (N-) doped NiTiO 3 materials [20]. Our result was also consistent with recent observation of a reduction in optical band gap in transition metal such as Mn-, Cr-doped lead-free ferroelectric Bi 0.5 Na 0.5 TiO 3 materials, and Fe-and Ni-doped Bi 0.5 K 0.5 TiO 3 materials which resulted from the spin splitting of transition metal under crystal field to make effect optical band gap [21][22][23]. Therefore, we suggested that the reduction of optical band gap energy in NiTiO 3 materials via Co-dopants resulted from the localization new state of Co ions.…”

FABRICATION AND PROPERTIES OF Co DOPED Bi0.5K0.5TiO3 – BiFeO3 SOLID SOLUTION

“…The reduction of the optical bandgap was possible originated from transition metal splitting under crystal field and oxygen vacancies was created due to unbalance charge between transition metal (Co 2+/3+ ) and host (Ti 4+ ) [16]. [17][18][19]. Recent studies of the BKT -BFO and BKT -BCO solid solutions, as well as Fe/Co -doped BKT, also reported the enhancement of the RT magnetic ordering together with the increase of Co/Fe concentration [14,16,17].…”