(Gd2-yMy)Ti2O7-y/2 (M = Ca, Sr)結構參數變化的研究

Structure parameters of (Gd2-yMy)Ti2O7-y/2 (M = Ca, Sr)

劉學明(Hsueh-Ming Liu)

指導教授 ： 高惠春

淡江大學/理學院/化學學系碩士班/碩士(2008年)

https://doi.org/10.6846/TKU.2008.00618

摘要

本研究使用聚合多質子酸先驅物法於不同溫度800 ~ 1400 oC下製備(Gd2-yMy)Ti2O7-y/2 (M = Ca, Sr; y = 0.050, 0.100)樣品，當燒結溫度為800 ~ 1400 oC時皆為焦綠石的結構，其空間群為Fd3m。樣品粒徑大小根據SEM圖中顯示大約為400 ~ 800 nm，緻密度為50 ~ 65%。隨燒結溫度的上升，單位晶胞a-軸的長度逐漸變大，長度為10.192(1) < a < 10.209(1) Å。Gd-O(1)和Ti-O(3)鍵長相同約為2.21(1) Å；Gd-O(2)鍵長較長約為2.52(1) Å；而Ti-O(2)鍵長相對較短約為1.97(1) Å。O(3)位置之佔有率也隨溫度升高而增加，使O(2)位置的x座標(fractional coordinate)受到O(3)位置的擠壓而有變大的趨勢。本系列樣品中Ti的價數經由XANES光譜的測量，推測沒有混價情形發生，為四價金屬離子。

關鍵字

(Gd2-yMy)Ti2O7-y/2 ； 焦綠石 ； 晶格參數 ； 聚合多質子酸先驅物法 ； XANES

並列摘要

Four samples with nominal compositions of (Gd2-yMy)Ti2O7-y/2 (M = Ca, Sr; y = 0.050, 0.100) were prepared with different temperatures from 700 - 1400 oC by a polymeric citrate precursor method. Pyrochlore phase with a space group of Fd3m was observed for all the samples except for those prepared at 700 oC. Particle size of (Gd2-yMy)Ti2O7-y/2 compounds are about 400 - 800 nm observed under SEM. Relative density of these samples are in the range of 50 - 65%. Unit cell a-axis (ea. 10.192(1) - 10.209(1) Å) and occupancy of the O(3) site (ea. 1 - 8%) increase with increasing the preparation temperature. Gd−O(1) and Ti−O(3) have the same bond length. They are about 2.21(1) Å. Gd−O(2) has a longer bond length, that is 2.52(1) Å. On the other hand, Ti−O(2) has a shorter bond length, that is about 1.97(1) Å. Increasing occupation factor of the O(3) site would increase the x fractional coordinate of the O(2) site. Ti L-edge XANES spectra show that all the samples have Ti(IV) valence state.

並列關鍵字

(Gd2-yMy)Ti2O7-y/2 ； pyrochlore ； lattice parameters ； polymeric citrate precursor method ； XANES

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