Synergistic effects of Ca2+ and high-valence Nb5+ co-doping on the structural, optical and magnetic properties of BiFeO3

Huimin Xian,Zhongquan Mao,Xi Chen,Jiang Zhang,Lingyun Tang

doi:10.1007/s10854-021-05685-0

Abstract

The structural, optical and magnetic properties of BiFeO3, BiFe0.99Nb0.01O3 and Bi1−xCaxFe0.99Nb0.01O3 (BCFNO, 0 ≤ x ≤ 0.25) nanoparticles synthesized via sol–gel method are investigated. It has been found that a phase transition from the rhombohedral R3c structure (x ≤ 0.10) to the ideal cubic perovskite structure (x = 0.25) which can be attributed to Ca2+ doping. Increasing Ca2+ dopants results in the increase of oxygen vacancies. As doping amount x increase, the bandgap of BCFNO decreases and the valence band spectra indicates that it’s a p-type semiconductor, which indicates their favorable potential in photocatalytic applications. The remnant magnetization Mr of BCFNO reaches a maximum value (0.146 emu/g about 15 times compared with pure BFO) at x = 0.10. This enhancement of magnetic properties in BCFNO can be ascribed to the synergistic effect of A and B site ions co-doping. Higher valance Nb doping cause the size effect and the magnetic polarons bounded to the impurities by Ca ions.

Highlights

Multiferroics are those materials which posses ferroelectric properties in combination with ferromagnetic properties in the same phase and have emerged as new appealing materials thanks to their enormous properties in the field of spintronic devices, dual storage devices, sensors, high density memory and multi-state electric devices[1][2][3]
The structural, optical and magnetic properties of BiFeO3, BiFe0.99Nb0.01O3 and Bi1 − xCaxFe0.99Nb0.01O3 (BCFNO, 0 ≤ x ≤ 0.25) nanoparticles synthesized via sol-gel method are investigated
Zhai et al.[16] observed structural transition from rhombohedral to monoclinic in La3+ doped BiFeO3 (BLFO) and improved coercive field and remanent magnetization with Nb doping at B site of BLFO

Summary

Introduction

Multiferroics are those materials which posses ferroelectric (or antiferroelectric) properties in combination with ferromagnetic (or antiferromagnetic) properties in the same phase and have emerged as new appealing materials thanks to their enormous properties in the field of spintronic devices, dual storage devices, sensors, high density memory and multi-state electric devices[1][2][3]. The room temperature phase of BiFeO3 possesses distorted rhombohedral perovskite structure as rhombohedral (R3c space group) with high ferroelectric Curie point (T ≈ 830°C), high antiferromagnetic(AFM) Neel temperature (T ≈ 370°C) and narrow band gap(2.16 eV)[4][5]. It’s highly investigated that BFO is characterized as a distorted perovskite rhombohedral structure (R3c space group) and a G-type antiferromagnetic (AFM) order modulated by a spatially spin structure along the [110]hex direction with a period of 62nm[6]. The focus was placed on investigating the effect of Ca2+ and Nb5+ co-doping on the crystal structures, morphologies, and optical and magnetic properties of as-prepared nanoparticles

Experimental Details

Structure analysis

Optical Properties

Magnetic Properties