We demonstrate a new modulation for a high-temperature polymorph of BaSrFe₄O₈ via synchrotron powder X-ray diffraction and transmission electron microscopy (TEM) experiments. Although the powder X-ray diffraction pattern was successfully analyzed using a structure model of space group $\mathit{Pnna}$, an unusually large isotropic atomic displacement parameter ($U_{\mathrm{iso}}$) was observed for the O1 atom. A split atom model that was applied to the O1 site and the adjacent Ba/Sr site, both of which are on the two-fold axis along the c-axis, indicated that positional disorder occurred in these atoms along the c-axis. The electron diffraction pattern and high-resolution TEM observations combined with the structure refinements revealed an incommensurate structure with a modulation vector $\mathit{q}=0.4270(1){\mathit{a}}^{*}$ and a displacement vector perpendicular to the a-axis, which gave rise to the large $U_{\mathrm{iso}}$ value of the O1 atom. The modulation observed in this study may be a signature of structural instability, which has commonly been discussed in the stuffed tridymite-type oxides.

我们通过同步加速器粉末X射线衍射和透射电子显微镜（TEM）实验证明了BaSrFe ₄ O ₈高温多晶型物的新调制。尽管使用空间群的结构模型成功地分析了粉末X射线衍射图$\mathit{普纳}$，是一个非常大的各向同性原子位移参数（${ü}_{\mathrm{iso}}$观察到O1原子。应用于O1位置和相邻的Ba / Sr位置的分裂原子模型都位于沿c轴的两倍轴上，这表明这些原子沿c轴发生了位置混乱。电子衍射图和高分辨率TEM观察与结构改进相结合，揭示了带有调制矢量的不对称结构$\mathit{q}=0.4270（\mathrm{1个}）{\mathit{一个}}^{*}$以及垂直于a轴的位移矢量${ü}_{\mathrm{iso}}$O1原子的值。在这项研究中观察到的调制可能是结构不稳定性的标志，这在填充的鳞石英型氧化物中已被普遍讨论。