Local Order and Oxygen Ion Conduction Induced High-Temperature Colossal Permittivity in Lead-Free Bi0.5Na0.5TiO3-Based Systems

New solid solution of Na0.5Bi0.5TiO3 with BaFeO3−δ materials were fabricated by sol–gel method. Analysis of X-ray diffraction patterns indicated that BaFeO3−δ materials existed as a well solid solution and resulted in distortion the structure of host Na0.5Bi0.5TiO3 materials. The randomly incorporated Fe and Ba cations in the host Na0.5Bi0.5TiO3 crystal decreased the optical band gap from 3.11 to 2.48 eV, and induced the room-temperature ferromagnetism. Our density-functional theory calculations further suggested that both Ba for Bi/Na-site and Fe dopant, regardless of the substitutional sites, in Na0.5Bi0.5TiO3 lead to the induced magnetism, which is illustrated in terms of the exchange splitting between spin subbands through the crystal field theory and Jahn–Teller distortion effects. Our work proposes a simple method for fabricating lead-free ferroelectric materials with ferromagnetism property for multifunctional applications in smart electronic devices.

Section: Resultsmentioning

confidence: 99%

Experimental and theoretical studies on induced ferromagnetism of new (1 − x)Na0.5Bi0.5TiO3 + xBaFeO3−δ solid solution

Dũng

Lam

Nguyen

et al. 2021

“…Both defects possibly induced ferromagnetism. In addition, the risk of O vacancies promoted the valence transition from Ti 4+ to Ti 3+ , thereby inducing ferromagnetism 55,60 . Moreover, the chemical strain due to the difference in the radii of Ca and Fe compared to that of the host lattice Bi 0.5 Na 0.5 TiO 3 materials might have tuned the ferromagnetic ordering, such as the Fe 3+ -□-Fe 3+ interaction or superinteraction of the magnetic polaron between [Fe 3+ -□-Fe 3+ ] versus [Fe 3+ -□-Fe 3+ ] etc.…”

mentioning

confidence: 99%

Intrinsic and tunable ferromagnetism in Bi0.5Na0.5TiO3 through CaFeO3-δ modification

Hung

Lam

Nguyen

et al. 2020

New (1-x)Bi 0.5 na 0.5 tio 3 + xcafeo 3-δ solid solution compounds were fabricated using a sol-gel method. the cafeo 3-δ materials were mixed into host Bi 0.5 na 0.5 tio 3 materials to form a solid solution that exhibited similar crystal symmetry to those of Bi 0.5 na 0.5 tio 3 phases. The random distribution of Ca and fe cations in the Bi 0.5 na 0.5 tio 3 crystals resulted in a distorted structure. The optical band gaps decreased from 3.11 eV for the pure Bi 0.5 na 0.5 tio 3 samples to 2.34 eV for the 9 mol% CaFeO 3-δ -modified Bi 0.5 na 0.5 tio 3 samples. Moreover, the Bi 0.5 na 0.5 tio 3 samples exhibited weak photoluminescence because of the intrinsic defects and suppressed photoluminescence with increasing cafeo 3-δ concentration. Experimental and theoretical studies via density functional theory calculations showed that pure Bi 0.5 na 0.5 tio 3 exhibited intrinsic ferromagnetism, which is associated with the possible presence of Bi, Na, and Ti vacancies and Ti 3+ -defect states. Further studies showed that such an induced magnetism by intrinsic defects can also be enhanced effectively with CaFeO 3-δ addition. This study provides a basis for understanding the role of secondary phase as a solid solution in Bi 0.5 na 0.5 tio 3 to facilitate the development of lead-free ferroelectric materials.The integration of room-temperature ferromagnetic behavior in lead-free ferroelectric materials is a new research trend for the development of green functional materials in smart electronic devices 1,2 . PbTiO 3 -based compounds are one of the most commonly used ferroelectric materials in electronic devices 3 . Therefore, ferroelectric PbTiO 3 -based materials with improved magnetic properties have the potential for the fabrication of next-generation electronic devices.First, the self-organized ferromagnetism of pure ferroelectric PbTiO 3 materials was investigated. The experimental results showed that the weak ferromagnetism in undoped PbTiO 3 nanocrystalline at room temperature resulted from intrinsic defects in events such as O and Ti vacancies 4 . PbTiO 3 thin films also exhibited room-temperature ferromagnetism because of defects in the crystal quality of the film during growth 5 . Shimada et al. predicted that both O and Ti vacancies induce ferromagnetism but through different mechanisms. The ferromagnetism driven by O vacancies originated from the spin-polarized e g state of the nearest Ti atom, whereas that directed by Ti vacancies was attributed to the half-metallic p x state of the nearest O atom 6 . In addition, the ferroelectric property of PbTiO 3 materials at room temperature could be attributed to O vacancies formed on the surfaces, such as vacancies induced ferromagnetism due to local non-stoichiometry and orbital symmetry breaking 7 . Xu et al. conducted first-principle calculations and reported that the O vacancies that formed at the domain wall led to magnetism with a localized spin moment around the vacancies 8 . Second, the conversion of transition metals to ferroelectric PbTiO 3 materials was studied...

“…The radius of Sr 2+ (1.44 Å) cations is larger than that of average A -site (Bi 3+ /Na + ) of 1.28 Å (Bi 3+ (1.17 Å)/Na + (1.39 Å)) 34 . However, the complex substitution of Sr 2+ cations for Bi 3+ or Na + cations in host lattice resulted in different behaviour, wherein Sr 2+ cations substituted for Bi 3+ cations generated the oxygen vacancies, whereas Sr 2+ cations replacing for Na + cations created the Na-vacancies 35 . Therefore, the Sr substitution in A -site was complex in distorted the lattice parameter.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, the vacancies of such Na-vacancies, which causes the substitution of Sr 2+ for Na + at A -site in perovskite structure, influenced the ferromagnetism in samples 14,17 . Moreover, if Sr 2+ cations substituted for Bi 3+ cations were possible resulted in changing the valence state of Ti 4+ to Ti 3+ state cause of enhancement the number of oxygen vacancies 35 . Our recently predicted that the Ti 3+ -defects state in Bi 0.5 K 0.5 TiO 3 materials was strong induced the ferromagnetism 51 .…”

Section: Resultsmentioning

confidence: 99%

Structure, optical and magnetic properties of new Bi0.5Na0.5TiO3- SrMnO3−δ solid solution materials

Dũng

Odkhuu

2019

The new Bi0.5Na0.5TiO3-SrMnO3−δ solid solution materials were fabricated via sol–gel method. The random incorporation of Sr and Mn cations into host lattice of Bi0.5Na0.5TiO3 resulted in structural distortion and influenced on the reduction of the optical band gap from 3.07 eV to 1.81 eV for pure Bi0.5Na0.5TiO3 and 9 mol% SrMnO3−δ solid solution into Bi0.5Na0.5TiO3. The magnetic properties of Bi0.5Na0.5TiO3 materials at room temperature were tuned via compensation of diamagnetic material with weak-ferromagnetism to ferromagnetism with low SrMnO3−δ content and combination of paramagnetism/antiferromagnetism-like and ferromagnetism with higher SrMnO3−δ content solid solution in Bi0.5Na0.5TiO3. The tunable magnetic and optical properties of lead-free ferroelectric materials was promising for their application to green electronic devices.