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Ferroelectricity of Dion-Jacobsen layered perovskites CsNdNb2O7 and RbNdNb2O7
Japanese Journal of Applied Physics ( IF 1.5 ) Pub Date : 2020-08-27 , DOI: 10.35848/1347-4065/abad46
Sota Asaki 1 , Hirofumi Akamatsu 1 , George Hasegawa 1 , Tomohiro Abe 2 , Yuki Nakahira 2 , Suguru Yoshida 1 , Chikako Moriyoshi 3 , Katsuro Hayashi 1
Affiliation  

Crystallography and dielectric properties in Dion-Jacobson layered perovskites, CsNdNb$_2$O$_7$ and RbNdNb$_2$O$_7$, have been examined in dense polycrystalline samples, and polarization hysteresis loops that substantiate ferroelectricity have been observed at room temperature. The theoretical mechanism for the spontaneous polarization, "hybrid improper ferroelectric mechanism,'' induced by a combination of two types of non-polar octahedral rotations, is confirmed in these two phases. Our samples show remanent polarizations of 2-3 $\mu$C/cm$^2$, which are much larger than those obtained in polycrystalline samples with the hybrid improper ferroelectricity reported so far. A dielectric constant in CsNdNb$_2$O$_7$ exhibits an anomaly at 625 K, corresponding to the ferroelectric transition, as previously revealed by x-ray and neutron diffractmetry. No dielectric anomaly is observed for RbNdNb$_2$O$_7$ throughout the temperature range studied here ($\leq$ 773 K), which is consistent with the previous diffractometry showing the persistence of polar $I2cm$ symmetry up to 790 K.

中文翻译:

Dion-Jacobsen 层状钙钛矿 CsNdNb2O7 和 RbNdNb2O7 的铁电性

Dion-Jacobson 层状钙钛矿 CsNdNb$_2$O$_7$ 和 RbNdNb$_2$O$_7$ 的晶体学和介电特性已在致密多晶样品中进行了检查,并在室温下观察到证实铁电性的极化滞后回线. 自发极化的理论机制,“混合不当铁电机制”,由两种类型的非极性八面体旋转的组合引起,在这两个阶段得到证实。我们的样品显示出 2-3 $\mu$ 的剩余极化C/cm$^2$,远大于目前报道的杂化铁电性不当的多晶样品中获得的值。CsNdNb$_2$O$_7$ 中的介电常数在 625 K 处表现出异常,对应于铁电体过渡,正如先前通过 X 射线和中子衍射所揭示的那样。在此处研究的整个温度范围内($\leq$ 773 K),没有观察到 RbNdNb$_2$O$_7$ 的介电异常,这与之前的衍射仪显示极性 $I2cm$ 对称性持续到 790 K 一致。
更新日期:2020-08-27
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