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    Electrical and magnetic properties of BSFO-NZF multiferroic composite ceramics
    (2025-06-01)
    Kaewsit, Sriwan
    ;
    Sompong, Khanisorn
    ;
    Pairindra, Worapong
    ;
    Pengpat, Kamonpan
    ;
    Yongsiri, Ploypailin
    This study involves the characterization and synthesis of (1-x)Bi<inf>0.9</inf>Sm<inf>0.1</inf>FeO<inf>3</inf> (BSFO) in association with (x)Ni<inf>0.6</inf>Zn<inf>0.4</inf>Fe<inf>2</inf>O<inf>4</inf> (NZF) multiferroic composite ceramics, utilizing x ratios of 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0, achieved through the high-energy planetary ball milling technique and conventional solid-state reaction method. X-ray diffraction confirms the formation of perovskite in the BSFO phase and spinel cubic structure in the NZF phase, absent from any elemental residues. It also signifies the successful incorporation of Sm ions into the BFO lattice. The utilization of field emission scanning electron microscopy (FESEM) combined with energy dispersive X-ray spectroscopy (EDX) for microstructural analysis demonstrates densified structures resulting from reduced grain sizes with the incorporation of NZF and verifies the composition percentages in the BSFO/NZF composite ceramic. The investigation of ferroelectric materials revealed that the ceramic hysteresis loop for the conditions of x = 0.3 and x = 0.5 demonstrated the most optimal ferroelectric behavior. The dielectric constant (ε<inf>r</inf>) exhibited composition-dependent behavior, decreasing from 4895.32 to 44.64 at 1 kHz with increasing NZF content, while demonstrating consistent frequency dispersion across 1 kHz to 1 MHz. Magnetic measurements conducted via vibrating sample magnetometry revealed a substantial increase in saturation magnetization from 0.24 emu/g to 80.06 emu/g as NZF concentration increased, under a maximum applied field of 20 kOe. Enhanced magnetic properties with preserved ferroelectricity enable potential magnetoelectric device applications. This study establishes systematic composition-property relationships that offer insights for optimizing multiferroic composites in practical applications such as sensors, actuators, and data storage devices.
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    Magnetization of NdFeB Permanent Magnet Considering Demagnetization Effect
    (2018-11-27)
    Sarikprueck, Piampoom
    ;
    Lumyong, Pichit
    ;
    Niroiana, Chamakorn Na
    ;
    Attaphong, Chodchanok
    Electrical machine efficiency improvement has been paid more attention over the past years. Using Permanent Magnets (PMs) in various modern electrical machines is one of the most favorable approaches to increase machine efficiency. However, PMs still have a significant disadvantage that is the demagnetization issue. Therefore, these demagnetized PMs need to magnetize for regaining their initial capability considering the demagnetization level. Therefore, first of all, this paper proposes the demagnetization behavior of NdFeB PMs due to thermal effect. Then, these PMs are magnetized using a proposed simple magnetizing technique considering various demagnetization conditions. Finally, the results indicate that the most complete demagnetized PMs are able to significantly recover to their initial capability.
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    Lattice evolution and point defect chemistry in Ta-doped ceria
    (2017-02-25)
    Charoonsuk, T.
    ;
    Vittayakorn, N.
    ;
    Kolodiazhnyi, T.
    Point defects in donor-doped ceria impact the physical, chemical and electronic properties. This work reports on the point defects in Ta-doped ceria, relating the changes in the lattice parameters with the type and concentration of point defects. The accurate Ce<sup>3+</sup> quantification using magnetization method is a key factor in solving the defect equilibria. Combining the experimental data and lattice expansion models it is demonstrated that the extra positive charge of Ta<sup>5+</sup> donors is compensated by both the Ce<sup>3+</sup> and the oxygen interstitials. An accurate quantitative analysis of the lattice expansion indicates that the theoretical calculations significantly overestimate the effect of the lattice response to oxygen interstitials. Furthermore, it is demonstrated that at high temperatures the anion Frenkel defects, whose concentration increases with the Ta substitution level, bring additional lattice expansion. The calculated enthalpy of formation of the anion Frenkel defects (H<inf>AF</inf> = 3.27–4.24 eV) for Ta-doped ceria is in good agreement with the ab-initio calculations and with the experimental values for the U-doped ceria. Furthermore, the accurate data of the lattice expansion caused by the interstitial oxygen reported here can be used to better understand and to predict the ‘swelling’ of the isomorphous UO<inf>2</inf>, PuO<inf>2</inf> and NpO<inf>2</inf> nuclear waste materials.