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通过制备和表征镧系元素的氧化物来模拟研究次锕系元素的混合氧化物固溶体的晶体结构。采用草酸盐共沉淀法和程序煅烧,得到了阳离子分布均匀的以CeO_2为本底的混合氧化物Ce_(1-x)Ln_xO_(2-x/2)(其中x∈[0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1];Ln=Nd、Sm)。利用红外光谱、拉曼光谱、热重分析和X射线衍射,表征了草酸盐前驱体(Ce_(1-x)Ln_x)_2(C_2O_4)_3·10H_2O的结构和特殊官能团,并使用X射线衍射法研究了Ce_(1-x)Ln_xO_(2-x/2)系列混合氧化物的晶体结构。结果表明,当固体氧化物中镧系元素含量较低时(对于Nd,x≤0.4;对于Sm,x≤0.3),可观察到典型的Fm-3 m萤石结构;当x较高(对于Nd,x≥0.5;对于Sm,x≥0.4)时,可观察到Ia-3立方结构。通过Rietveld方法计算晶格常数,表明其与平均阳离子半径遵从一种二次关系,这种二次关系是逐渐增长的平均阳离子半径和由于氧空位造成的O-O斥力减少综合作用的结果。
The crystal structure of the mixed oxide solid solution of actinides was studied by means of preparation and characterization of lanthanide oxides. The mixed oxide Ce_ (1-x) Ln_xO_ (2-x / 2) with uniform cation distribution was obtained by the oxalate coprecipitation method and programmed calcination (where x∈ [0,0.1,0.2 , 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1]; Ln = Nd, Sm). The structures and special functional groups of the oxalate precursor (Ce_ (1-x) Ln_x) _2 (C_2O_4) _3 · 10H_2O were characterized by infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis and X-ray diffraction. The crystal structure of Ce_ (1-x) Ln_xO_ (2-x / 2) mixed oxides has been studied. The results show that a typical Fm-3m fluorite structure can be observed when the Lanthanide content in the solid oxide is low (x≤0.4 for Nd and x≤0.3 for Sm); when x is high (for Nd, x ≧ 0.5 and x ≧ 0.4 for Sm), the cubic structure of Ia-3 can be observed. The calculation of the lattice constant by the Rietveld method shows that it follows a quadratic relationship with the average cationic radius as a result of the combined effect of a gradually increasing average cationic radius and the reduction of O-O repulsion due to oxygen vacancies.