铈基镧系氧化物的制备与晶体结构变化

Elaboration and Crystal Structure Change of Cerium-Based Lanthanide Oxides

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。

In this paper,the mixed oxides of non-radioactive lanthanides were prepared in order to simulate the mixed oxides of minor actinides,as their chemical properties are similar.CeO_2-based mixed oxides Ce_（1-x）Ln_xO_（2-x/2） with Ln=Nd or Sm and x∈ [0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1]were prepared through calcination of the oxalate precursors（Ce_（1-x）Ln_x）_2（C_2O_4）_3·10H_2O elaborated by coprecipitation method which led to a homogeneous distribution of cations in the mixed oxides.For the characterization,the infrared spectroscopy,Raman spectroscopy,X-ray diffraction and thermo-gravimetric analysis were applied for the oxalate precursors.Then investigations of the crystalline structure ofthese oxides Ce_（1-x）Ln_xO_（2-x/2） were carried out by X-ray diffraction.Typical fluorite Fm 3m structure is observed for relatively low Ln^（3＋） contents（x≤0.4for Nd and x≤0.3for Sm）,then a cubic Ia-3structure is observed（x≥0.5for Nd and x≥0.4for Sm）.In addition,the Rietveld method was used for refining the unit cell parameters of Ce_（1-x）Ln_xO_（2-x/2）.The variation of the unit cell parameters in different series is found to follow a quadratic relation as a result of combination between increasing cationic radius and decreasing O-O repulsion caused by oxygen vacancies.