کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1518828 | 1511626 | 2006 | 9 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Synthesis and structure refinement of layered perovskites Ba5âxLaxNb4âxTixO15 (x=0, 1, 2, 3 and 4) solid solutions
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی مواد
مواد الکترونیکی، نوری و مغناطیسی
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چکیده انگلیسی
Ba5âxLaxNb4âxTixO15 solid solutions were prepared by solid state reaction method. Structural analysis for the stoichiometric phases was performed for x=0, 1, 2 and 3 by Rietveld analysis of neutron powder diffraction data. The x=0, 1 and 2 members could be refined in the space group P-3m1 (stacking sequence chhcc, polytypoid 5Â H). There is a decrease in cell volume as x increases. La3+ occupies preferentially the A2 site (Wyckoff site 2d) and Ti4+ the B2 site (Wyckoff site 2c). As x increases there is an increase of the global instability index (GII) (which is a measure of the extent to which the BVS rule is violated over the whole structure) indicating the presence of intrinsic strains large enough to cause instability at room temperature. This strain is responsible for a structural change for the member with x=3, which could be refined in the space group P-3c1 (stacking sequence (chhcc)2, polytypoid 2Ã5H=10H). This change in space group is associated with a cooperative rotation of (Nb/Ti)O6 octahedra around the c-axis, necessary to accommodate the smaller La3+ ion in the cuboctahedral cavity.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Physics and Chemistry of Solids - Volume 67, Issue 7, July 2006, Pages 1558-1566
Journal: Journal of Physics and Chemistry of Solids - Volume 67, Issue 7, July 2006, Pages 1558-1566
نویسندگان
J.M. De Paoli, J.A. Alonso, R.E. Carbonio,