通过增加钡含量减少SrxBa1-xNb2O6中NbO6-octahedra的位置调制：室温下x=0.61和x=0.34的单晶中子衍射研究
Reducing the positional modulation of NbO6-octahedra in SrxBa1-xNb2O6 by increasing the Barium content: A single crystal neutron diffraction study at ambient temperature for x=0.61 and x=0.34
摘要：
通过对比Sr0.61Ba0.39Nb2O6（SBN 61）和Sr0.34Ba0.66Nb2O6（SBN 34），研究了Ba含量对SrxBa_（1-x）Nb_2O_6调制幅度的影响。我们的单晶中子衍射结果表明，NbO 6八面体的位置调制的幅度随着钡含量的增加而减小，这表明调制的起源是Sr和Ba原子对五边形通道的部分占据。通过增加Sr含量，较大的Ba原子被较小的Sr原子取代，这导致周围晶格的较大变形，从而导致较大的调制幅度。用一种原子类型（Ba）填充这些通道越均匀，调制幅度越低。我们的结果还表明，该结构可以用二维无公度谐波调制来描述。通过单晶衍射测量和q扫描都没有观察到二阶调制。Nb原子的位置调制比氧原子的位置调制小得多，因此该调制可以被视为几乎刚性的NbO 6-八面体的旋转调制。
英文摘要：
We report on the influence of the Barium content on the modulation amplitude in SrxBa1-xNb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.
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