| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 102 === A series of silicon doped Lanthanum-Germanates apatite-type materials, La10Ge6-xSixO27 (x=0, 1.2, 2.4, 3.6, 4.8, 6) were prepared in an attempt to synthesize a single phase by solid-state method. Moreover, in order to observe the relationship between changes in the crystal structure and electrical conductivity when Si4+ with different content were doped into the Ge4+ sites of tetrahedra, single phase La9.5Ge6-xSixO26.25 (x= 0, 0.6, 1.2, 1.8, 2.4, 3.6, 4.8, 6) series were prepared using the solid-state method.
In the La10Ge6-xSixO27 series, the XRD pattern results indicated that lots of second phases existed and that the diffraction peak broadened when x=0; non-reacted La2O3 and second phase La2SiO5 existed when x=6. Thus, it’s difficult to synthesize a single phase using athe solid-state method.
In the La9.5Ge6-xSixO26.25 series, the XRD pattern results indicated that second phase La2SiO5 existed when x=3.6. Therefore, the solid solubility limit is about x =2.4, and the single phase calcination temperature increases as Si4+ content increases. Subsequently, five single phase powder samples, La9.5Ge6-xSixO26.25 (x=0, 0.6, 1.2, 1.8, 2.4) were selected to calculate lattice parameters using the Rietveld method as well as to analyze changes in the crystal structure; and the same five over-95% relative density bulks were selected to measure electrical conductivity. The results indicated that x=1.8 exhibited the highest conductivity at 800℃ (0.0335 S/cm), and that in the crystal structure analysis, x=1.8 had longest O3-O4 distance (3.3430Å) and the longest O3-La2 (longer) distance (3.4725Å). This indicated that x=1.8 had more space to allow oxygen ion for migration. Furthermore, the exsiting interstitial oxygen regions were around the O3-La2 (longer) space, and exhibited a sinusoidal-like path along the c-axis.
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