| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 101 === Lithnium niobate (LiNbO3) can be obtained by mixing lithium nitrate (LiNO3), ammonium niobate oxalate hydrate (C4H4NNbO9) and glycine and then calcining at 600oC for 1 h. The thermal analysis, structure, morphology, and dielectric property of the as-prepared LiNbO3 were characterized by thermogravimetric and differential thermal analyses (TG/DTA), X-ray diffraction (XRD) , Raman spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and multimeter. The crystallization temperature of LiNbO3 precursor is 580 oC based on the TG/DTA results. After being calcined at 600oC, the structure of the LiNbO3 synthesized using various ratios of glycine to metal nitrates (Ψ-value) was formed with a particle size of about 29–38 nm, as found by XRD analysis. The crystal size has the lowest value at Ψ= 2, and the highest level of crystallization is at Ψ= 3.When the calcination temperature reached 900 oC, the secondary phases Li3NbO4 and LiNb3O8 were observed. The lithium concentration before 900oC was 40–43%. When the calcination temperature was higher than 900oC, the major Li0.91NbO3 phase and the minor LiNbO3 phase coexisted in the nonstoichiometric lithium niobate with 43% lithium content.
After sintering at 1100oC, the structure of the Li0.43Nb0.57O3+δ was similar to the single crystal of lithium niobate. The thermal vibration of the elements caused the bond length of the NbO6 framework and angle bending of the O-Nb-O to increase, and the structure was restored by the formation of square crystals in the quasi-melting Li0.43Nb0.57O3+δ matrix. The dielectric constant increased with the increasing sintering temperature before 1000 oC, and then fell due the formation of split seam . The reduction in defects forming from the Li-site vacancies lowered the dissipation factor at higher sintering temperatures.
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