Intrinsic and tunable ferromagnetism in Bi0.5Na0.5TiO3 through CaFeO3-\u03b4 modification

N T Hung,T Ochirkhuyag,D D Dung,N N Trung,Y S Kim,A D Nguyen,N Tsogbadrakh N Tsogbadrakh,N H Lam,L H Bac,D Odkhuu

doi:10.1038/s41598-020-62889-w

N T Hung, T Ochirkhuyag + Show 8 more

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https://doi.org/10.1038/s41598-020-62889-w

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Abstract

New (1-x)Bi0.5Na0.5TiO3 + xCaFeO3-δ solid solution compounds were fabricated using a sol–gel method. The CaFeO3-δ materials were mixed into host Bi0.5Na0.5TiO3 materials to form a solid solution that exhibited similar crystal symmetry to those of Bi0.5Na0.5TiO3 phases. The random distribution of Ca and Fe cations in the Bi0.5Na0.5TiO3 crystals resulted in a distorted structure. The optical band gaps decreased from 3.11 eV for the pure Bi0.5Na0.5TiO3 samples to 2.34 eV for the 9 mol% CaFeO3-δ-modified Bi0.5Na0.5TiO3 samples. Moreover, the Bi0.5Na0.5TiO3 samples exhibited weak photoluminescence because of the intrinsic defects and suppressed photoluminescence with increasing CaFeO3-δ concentration. Experimental and theoretical studies via density functional theory calculations showed that pure Bi0.5Na0.5TiO3 exhibited intrinsic ferromagnetism, which is associated with the possible presence of Bi, Na, and Ti vacancies and Ti3+-defect states. Further studies showed that such an induced magnetism by intrinsic defects can also be enhanced effectively with CaFeO3-δ addition. This study provides a basis for understanding the role of secondary phase as a solid solution in Bi0.5Na0.5TiO3 to facilitate the development of lead-free ferroelectric materials.

Highlights

New (1-x)Bi0.5Na0.5TiO3 + xCaFeO3-δ solid solution compounds were fabricated using a sol–gel method
The experimental results showed that the weak ferromagnetism in undoped PbTiO3 nanocrystalline at room temperature resulted from intrinsic defects in events such as O and Ti vacancies[4]
The X-ray diffraction (XRD) patterns of CaFeO3-δ-modified Bi0.5Na0.5TiO3 with a CaFeO3-δ concentration of up to 9 mol.% showed that CaFeO3-δ was well dissolved in the host Bi0.5Na0.5TiO3 crystal

Summary

Introduction

New (1-x)Bi0.5Na0.5TiO3 + xCaFeO3-δ solid solution compounds were fabricated using a sol–gel method. Experimental and theoretical studies via density functional theory calculations showed that pure Bi0.5Na0.5TiO3 exhibited intrinsic ferromagnetism, which is associated with the possible presence of Bi, Na, and Ti vacancies and Ti3+-defect states. Further studies showed that such an induced magnetism by intrinsic defects can be enhanced effectively with CaFeO3-δ addition. 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]. Ferroelectric PbTiO3-based materials with improved magnetic properties have the potential for the fabrication of next-generation electronic devices. The ferroelectric property of PbTiO3 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]. There is a strong need for green ferroelectric materials to replace Pb-based ferroelectric in electronic device application

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