The structures of the Ce and LaN-phases RE3Si8-xAlxN11-xO4+x (x≈1.75 for RE = Ce, x ≈ 1.5 for RE = La), determined by single-crystal X-ray and time-of-flight neutron powder diffraction, respectively
The structures of the Ce and LaN-phases RE3Si8-xAlxN11-xO4+x (x≈1.75 for RE = Ce, x ≈ 1.5 for RE = La), determined by single-crystal X-ray and time-of-flight neutron powder diffraction, respectively
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DOI：
10.1039/b102340n
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发表时间：
2001-01-01
影响因子：
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通讯作者：
Berastegui, P
中科院分区：
文献类型：
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作者：
Grins, J;Shen, ZJ;Berastegui, P
通过一种新的途径获得了Sialon Ce-N相Ce3Si8-xAlxN11-xO4+x(x约为1.75)的单晶，即首先用快速致密化技术制备相组成远离热动态平衡的完全致密体，然后在Sialon粉床中于1600℃的N-2气氛中热处理24 h，用Mokα单晶数据和直接方法对Ce N相的结构进行了解析。在空间群I2/a中进行了精炼，a=15.798(1)。B=114.816(3)，c=17.990(1)埃，β=114.816(4)度，V=1262.4埃(3)，到加权R(F-OBS(2))=6.7%。利用飞行时间中子粉末衍射数据，用La原子和N/O原子的各向异性热参数修正了La的各向异性相结构。其中4/15为N原子，与3个Si/Al原子配位，2/15为四面体自由顶点O原子，并与3个Ce/La原子配位，其余9/15位于N和O原子占据的位置上，分别与2个四面体Si/Al原子和1-2个Ce/La原子配位。与以前由固体核磁共振谱推导出的结构方案进行了比较。
Single crystals of the sialon Ce N-phase Ce3Si8-xAlxN11-xO4+x (x approximate to 1.75) were obtained via a novel route, i.e. by first preparing a fully compacted body with phase constitutions far away from thermal dynamic equilibrium by means of a fast densification technique, spark plasma sintering, and then heat treating this compact in a sialon powder bed at 1600 degreesC in N-2 atmosphere for 24 h. The structure of the Ce N-phase was solved using MoK alpha single-crystal data and direct methods. It was refined in space group I2/a with a = 15.798(1). b = 4.8939(3), c = 17.990(1) Angstrom, beta = 114.816(4)degrees, V = 1262.4 Angstrom (3), to a weighted R(F-obs(2)) = 6.7% for 977 unique reflections. The isostructural La phase structure was refined with anisotropic thermal parameters for La and N/O atoms using time-of flight neutron powder diffraction data. The structure exhibits three structural kinds of N/O anions: 4/15 of these are N atoms which are triangularly coordinated by 3 Si/Al atoms, 2/15 are tetrahedron free apex O atoms which are in addition bonded to 3 Ce/La atoms while the remaining 9/15 are on sites that are statistically occupied by N and O atoms and which are bonded to 2 tetrahedral Si/Al atoms and 1-2 Ce/La atoms. Comparisons are made with a previous structural proposal deduced from solid state nuclear magnetic resonance spectra.