Size effect on crystal structure and chemical bonding nature in BaTiO3 nanopowder
Size effect on crystal structure and chemical bonding nature in BaTiO3 nanopowder
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DOI：
10.1007/s10973-005-0834-z
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发表时间：
2005-08-01
影响因子：
4.4
通讯作者：
Atake, T
中科院分区：
文献类型：
--
作者：
Aoyagi, S;Kuroiwa, Y;Atake, T
用高能同步辐射粉末衍射法研究了几种粒径为50 nm的BaTiO_3纳米粉末的尺寸效应对晶体结构的影响，包括化学键性质。Rietveld分析表明，在300K时，BaTiO_3纳米粉末由四方结构和立方结构组成，其共存特征可用核/壳模型来描述，其中立方结构的壳层以四方结构覆盖核心。立方壳的厚度几乎是恒定的，与颗粒大小无关，估计约为8 nm。因此，建议将整个颗粒被立方壳覆盖的临界颗粒尺寸定为16 nm。用最大熵方法研究了410K时BaTiO3纳米粉末在立方相中的电荷密度分布。与大块晶体相比，50 nm晶体的成键电子密度和离子价态的变化并不明显。
The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.