Fast-cooling after sintering or annealing of BiFeO3-BaTiO3 mixed oxide ceramics yields coreshell structures that give excellent functional properties, but their precise phase assemblage and nanostructure remains an open question. By comparing conventional electron energy loss spectroscopy (EELS) with scanning precession electron diffraction (SPED) mapping using a direct electron detector, we correlate chemical composition with the presence or absence of octahedral tilting and with changes in lattice parameters. This reveals that some grains have a 3-phase assemblage of a BaTiO3-rich pseudocubic shell; a BiFeO3-rich outer core with octahedral tilting consistent with an R3c structure; and an inner core richer in Ba and even poorer in Ti, which seems to show a pseudocubic structure of slightly smaller lattice parameter than the shell region. This last structure has not been previously identified in these materials, but the composition and structure fit with previous studies. These inner cores are likely to be non-polar and play no part in the ferroelectric properties. Nevertheless, the combination of EELS and SPED clearly provides a novel way to examine heterogeneous microstructures with high spatial resolution, thus revealing the presence of phases that may be too subtle to detect with more conventional techniques.

中文翻译：

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伪二元 0.75Bi(Fe 0.97 Ti 0.03 )O 3 –0.25BaTiO 3 陶瓷的相关化学和结构纳米表征

BiFeO3-BaTiO3 混合氧化物陶瓷在烧结或退火后快速冷却会产生具有优异功能特性的核壳结构，但其精确的相组合和纳米结构仍然是一个悬而未决的问题。通过比较传统的电子能量损失光谱 (EELS) 与使用直接电子检测器的扫描进动电子衍射 (SPED) 映射，我们将化学成分与八面体倾斜的存在或不存在以及晶格参数的变化相关联。这表明一些晶粒具有富含 BaTiO3 的假立方壳的三相组合；富含 BiFeO3 的外核，八面体倾斜，符合 R3c 结构；内核的 Ba 含量更高，Ti 含量更低，这似乎显示出晶格参数比壳区略小的伪立方结构。这最后一种结构以前没有在这些材料中被发现，但其组成和结构符合以前的研究。这些内核很可能是非极性的，对铁电特性没有影响。尽管如此，EELS 和 SPED 的结合显然提供了一种以高空间分辨率检查异质微观结构的新方法，从而揭示了可能太微妙而无法用更传统的技术检测的相的存在。