Effect of Fe3+ doping on the ferrielectric and magnetic properties of KNbO3 ceramics

• Published in: Physica. B, Condensed matter Condensed matter, 2021-11, Vol.621, p.413308, Article 413308
• Main Authors: Song, Guilin, Chen, Lei, Xing, Luyao, Zhang, Ke, Wu, Zengyuan, Yang, Haigang, Zhang, Na
• Format: Article
• Language: English
• Subjects: Bound magnetic polarons; Ceramics; Crystal defects; Defect dipole; Dipoles; Doping; Ferric ions; Ferroelectric polarization; Ferroelectricity; Ferrous ions; Grain size; KNbO3; Magnetic properties; Magnetism; Morphology; Paramagnetism; Polarons; Potassium niobates; Semiconductor doping
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2021.413308

KNb1-xFexO3(x = 0–0.2) ceramics are prepared by the self-sacrificing method. The effects of Fe ion doping on the ferroelectricity, and magnetic properties of KNbO3 are studied. XRD analysis shows that all samples belong to the single-phase orthorhombic system with the space group of Amm2. The XPS test proves that Fe ions exist in the form of +2 and + 3 valence in KNbO3 sample, and the ratio of Fe2+/Fe3+ in the sample is calculated. SEM shows that Fe ions doping has a significant regulating effect on the microscopic morphology and grain size of KNbO3 sample. Fe ions partially replace Nb5+ in the B site of KNbO3 crystals, three kinds of defect dipoles of [FeNb``−VO··]*, [VO··−FeNb```−VO··]·and polarity[FeNb```−VO··]·are formed. The polarization of the defect dipole is one of the main factors that enhance the ferroelectricity of KNbO3 crystal. The interaction between Fe3+/Fe2+ and adjacent VO··to form Fe2+/3+-VO·· bound magnetic polarons is considered to be the main source of paramagnetism for KNb1-xFexO3(x = 0–0.2) samples. when x ≤ 0.1, Fe ions mainly exist in KNO sample in the form of Fe2+/3+-VO··bound magnetic polaron, x > 0.1, it mainly exists in the ceramic in the form of Fe–O–Fe super-exchange. M value of KNb1-xFexO3 (x = 0.05–0.2) samples has a linear relationship with the increase of temperatures (T) when T ≥ 100K, indicating that samples exhibits paramagnetism. The magnetic properties at different doping concentrations and different temperatures may be isolated Fe3+, Fe2+, Fe2+/3+-VO··, Fe3+-O2--Fe3+ and Fe2+-O2--Fe3+ is the result of the combined effect. •XPS test proves that Fe ions exist in the form of +2 and +3 valence states, and the ratio of Fe2+/Fe3+ in the samples is calculated.•when x≤0.1, Fe ions mainly exist in KNO sample in the form of Fe2+/3+-VO ∙∙ bound magnetic polaron, x>0.1, it mainly exists in the ceramic in the form of Fe-O-Fe super-exchange.•It is found that the peak of 240K is the phase transition of the KNO crystal structure from rhombic to orthorhombic system.