Lanthanum pyrochlores and the effect of yttrium addition in the systems La2−xYxZr2O7 and La2−xYxHf2O7
Lanthanum pyrochlores and the effect of yttrium addition in the systems La2−xYxZr2O7 and La2−xYxHf2O7
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DOI：
10.1016/j.jssc.2008.11.008
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发表时间：
2009-03
影响因子：
3.3
通讯作者：
K. Whittle;L. Cranswick;Simon A. T. Redfern;I. Swainson;G. Lumpkin
中科院分区：
文献类型：
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作者：
K. Whittle;L. Cranswick;Simon A. T. Redfern;I. Swainson;G. Lumpkin
用中子粉末衍射和电子显微镜研究了La 2-xYxZr 2 O 7和La 2-xYxHf 2 O 7（x=0.0，0.4，0.8，1.2，1.6和2.0）的晶体结构，确定了烧绿石和萤石固溶体的稳定场。烧绿石在这些固溶体中的稳定极限分别接近于La 0.8Y 1.2Zr 2 O 7和La 0.4Y 1.6Hf 2 O 7。在这两个系统中的晶胞参数被发现与Y含量线性变化，在这些组合物中的烧绿石相是稳定的，作为48 f（x，38，38）网站上的氧原子的x坐标。在这两个系统中，烧绿石数据的线性外推表明，无序伴随着晶格参数的约0.4%的小的减少。当达到烧绿石固溶体极限后，由于有利于无序缺陷萤石结构，观察到从x = 0.41到0.375的急剧变化。电子衍射图表明，一些短程有序仍然在无序的缺陷萤石相。
The crystal structures of the compounds La2−xYxZr2O7and La2−xYxHf2O7with x=0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 have been studied using neutron powder diffraction and electron microscopy to determine the stability fields of the pyrochlore and fluorite solid solutions. The limits of pyrochlore stability in these solid solutions are found to be close to La0.8Y1.2Zr2O7and La0.4Y1.6Hf2O7, respectively. In both systems the unit cell parameter is found to vary linearly with Y content across those compositions where the pyrochlore phase is stable, as does the x-coordinate of the oxygen atoms on the 48f (x,38,38) sites. In both systems, linear extrapolations of the pyrochlore data suggest that the disordering is accompanied by a small decrease in the lattice parameter of approximately 0.4%. After the pyrochlore solid solution limit is reached, a sharp change is observed from x∼0.41 to 0.375 as the disordered defect fluorite structure is favoured. Electron diffraction patterns illustrate that some short-range order remains in the disordered defect fluorite phases.