Oxygen vacancy-induced ferromagnetism in Bi4NdTi3FeO15 multiferroic ceramics

Abstract

Layered Aurivillius compounds with multiferroic properties have attracted much attention due to their rich fundamental physics and great application potential. However, the ferroelectric and magnetic properties are different for these compounds with different synthesis conditions. In this paper, we investigate the structure, ferroelectricity, and magnetism of four-layer Aurivillius-phase multiferroic Bi4NdTi3FeO15. The four-layer structure is confirmed by powder X-ray diffraction and high-angle annular dark field scanning transmission electron microscopy. The ferroelectricity together with dielectric constant can be reduced by vacuum-annealing treatment due to the increase of oxygen vacancy concentration. More interestingly, the ferromagnetism is strongly enhanced by vacuum-annealing and can be obviously suppressed after re-oxidization, which may be associated with Fe3+-O-Fe2+ coupling originated from the variable valence state of Fe with different oxidization conditions. These findings indicate that oxygen vacancies play a crucial role in the ferroelectric and magnetic properties in Aurivillius compounds synthesized by different conditions.

Progress and Perspectives on Aurivillius-Type Layered Ferroelectric Oxides in Binary Bi4Ti3O12-BiFeO3 System for Multifunctional Applications

“…We also observed the structural evolution of Srdoped Bi 7 Fe 1.5 Co 1.5 Ti [160]. In addition, Zhang et al [22] reported Bi 4 NdTi 3 Fe 1−x Co x O 15 compounds suffer a structural evolution from the four-layer phase to three-layer phase with increasing Co doping level from 0 to 1, and they found the compounds with different ratios of four-and three-layered structure present a significant variation of FE and magnetic properties. Wang et al [161] reported that Bi 5 Ti 3 Fe 1−x Co x O 15 forms single four-like layer perovskite structures for x < 0.67, while three-like layer perovskite begins to arise for x > 0.67, suggesting a structural transformation, and the weak RT FM properties only exist in the materials with the mixed-layer structure, as shown in Figure 6g.…”

“…The ion substitution would influence the inter-strain and tolerance factor. The A-site can be occupied by large cations such as Na + [20], K + [107], Ca 2+ [108], Sr 2+ [46], Ba 2+ [26], Pb 2+ [109], Y 3+ [21], Bi 3+ and Ln (La [27], Nd [22], Sm [23], Gd [24], Ce [110][111][112],Tb [25], Dy [113], Ho [114], Er [115,116], Eu [56], Yb, Th [117], Pr [118]), the B-site can accommodate hetero-valent elements (Ti 4+ , W 6+ [36], Nb 5+ [43], Ta 5+ [119], V 5+ , Cu 2+ [120], Mo 6+ [121], and Mg 2+ [43]) and a variety of magnetic elements (Fe, Cr, Mn, Co, and Ni) [32][33][34][35][36][37][38][39][40][41][42][43][44]52], which will create the possibility of magnetic ordering. More interestingly, the halogen or nitrogen elements substitution on the O-sites was accomplished [122,123].…”

“…In the last decade, numerous pieces of research focused on the BFTO-n with integer n, for example, Bi 5 FeTi 3 O 15 , Bi 6 Fe 2 Ti 3 O 18 , and Bi 7 Fe 3 Ti 3 O 21 . The reported studies have mainly embodied two aspects: (i) doping ions into A-sites [19][20][21][22][23][24][25][26][27][28][29] and/or substituting magnetic transition ions into B-sites [30][31][32][33][34][35][36][37][38][39][40][41][42][43] inside the layered perovskite structure to realize a significant enhancement in the multiferroic performances, and (ii) controllable synthesis of materials in ceramics [44][45][46], thin films [47][48][49][50][51][52], nano-crystallines [53][54][55][56][57][58] and single crystals [59][60][61] to observe the growth process [62][63][64]…”

Photocurrent density and electrical properties of Bi0.5Na0.5TiO3-BaNi0.5Nb0.5O3 ceramics

“…Unfortunately, the bandgaps of most perovskite-oxide ferroelectrics are higher than 3.2 eV. For energy utilization, ferroelectric materials absorbing ultraviolet (UV) rays containing only 3.5% of solar radiation intensity are of little significance [17]. Therefore, an adjustable narrow-band gap is of great significance for improving the photovoltaic effect of ferroelectric materials.…”

Structure Evolution and Multiferroic Properties in Cobalt Doped Bi4NdTi3Fe1-xCoxO15-Bi3NdTi2Fe1-xCoxO12-δ Intergrowth Aurivillius Compounds

“…The series of Aurivillius phase compounds are well known for their excellent ferroelectric properties with very low fatigue12, and offer great potential for tailoring specific properties by varying different ionic compositions or even number of layers81314. By doping with magnetic cations, the bismuth-based Aurivillius phase compounds were found to have a room temperature ferromagnetic order besides the natural ferroelectricity, indicating their multiferroic potential89151617. Moreover, the Sm and Co co-doped 3-layered ( n  = 3) Bi 4- x Sm x Ti 3- x Co x O 12-δ (0 ≤  x  ≤ 0.07) ceramics show a magnetoelectric (ME) coupling coefficient of 0.65 mV/cm∙Oe at room temperature15, while the 5-layered ( n  = 5) SrBi 5 Fe 0.5 Co 0.5 Ti 5 O 18 ceramic was found to show a ME coupling coefficient of 0.27 mV/cm∙Oe8.…”