Document Details
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Document Type |
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Thesis |
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Document Title |
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Lanthanum orthoferrites. Facile synthesis, characterization and electromagnetic properties لانثانيوم اورثوفريت. التحضير السهل، التوصيف و الخواص الكهرومغناطيسيه |
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Subject |
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Faculty of Science |
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Document Language |
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Arabic |
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Abstract |
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LaFeO3 was prepared via simple, economical and environmentally friendly auto-combustion methods using different fuels, including citrate, urea, sucrose, egg whites, gelatin and chitosan. The prepared ferrites were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high resolution transmission electron microscopy (HRTEM), vibrating sample magnetometery (VSM) and electrical measurements to study the impact of the synthetic routes on the various properties. XRD showed the formation of a single orthorhombic phase, except for the samples prepared via egg white, gelatin and urea methods, which indicated a secondary La2O2CO3 phase. The FT-IR and TEM studies confirmed the formation of the phase. Differential thermal analysis-thermogravimetry techniques (DTA-TG) were used to characterize the auto-combustion process up to ferrite formation. The obtained unsaturated magnetization for all of the samples suggested the presence of anti-ferromagnetic ordering in addition to weak ferromagnetic ordering. The egg white method showed higher magnetization (1.78 emu/g), while the urea and chitosan methods indicated lower magnetization (0.13 emu/g). The coercivity measurements confirmed the presence of ferromagnetic/anti-ferromagnetic interfaces with higher values than some those reported in the literature. The AC-conductivity measurements indicated semiconducting characteristics and exhibited a change in the conduction mechanism from hopping to polaron conduction by increasing the temperature. LaFeO3 prepared via the egg white method indicated an anti-ferromagnetic/paramagnetic transition at approximately 715 K. The dielectric measurements confirmed the AC-conductivity results and exhibited values higher than some those reported in the literature. Depending on results the particle size and phase formation, a series of Sr-substituted lanthanum orthoferrite perovskites; La1‐xSrxFeO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared using the sucrose assisted auto-combustion route to study the effect of Sr-substitution on the structural, magnetic and electrical properties and to investigate the impact of the entire method on different properties. The obtained different phases were characterized using different techniques. XRD revealed peaks attributed to SrCO3 secondary phase increases in their intensity by increasing Sr-content till predominate at x = 1.0. It also showed a transfer from orthorhombic symmetry to rhombohedral one by increasing Sr-content. The obvious contraction in the unit cell parameters by Sr-substitution could be attributed to the Fe3+ → Fe4+ oxidation occurred to balance the total charge on molecule. The obvious increase in the magnetization by increasing Sr could be attributed to the formation of Fe4+ ions, strengthen the ferromagnetic component through sharing in the double exchange interaction; Fe4+-O-Fe3+ as well as the formation of oxygen vacancies that disturb the uncompensated surface spin. Ac-conductivity measurements indicated a change in the entire conduction mechanism from electronic to ionic with improving conductivity by increasing Sr-content. Generally, the utilized sucrose method indicated an improvement in the obtained magnetization accompanied by lowering conductivity than previously reported systems in literature. |
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Supervisor |
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Prof. Dr. Mohamed Gabal |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1441 AH
2020 AD |
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Co-Supervisor |
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Prof. Dr. Yasser. Al Angari |
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Added Date |
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Sunday, May 17, 2020 |
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Researchers
| فاطمة محمد السلمي | Al Solami, Fatimah Mohammed | Researcher | Doctorate | |
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