The absence of ferroelectric polarization in layered and rock-salt ordered NaLnMnWO6 (Ln = La, Nd, Tb) perovskites.
The absence of ferroelectric polarization in layered and rock-salt ordered NaLnMnWO6 (Ln = La, Nd, Tb) perovskites.
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DOI：
10.1039/c3cp54776k
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
Chandan De;Tai-Hoon Kim;K. Kim;A. Sundaresan
中科院分区：
文献类型：
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作者：
Chandan De;Tai-Hoon Kim;K. Kim;A. Sundaresan
有序钙钛矿NaLnMnWO_6（Ln = La，Nd，Tb）具有层状结构中A位阳离子（Na和Ln）和岩盐结构中B位阳离子（Mn和W）的同时有序性。它们已被证明以单斜结构结晶，极性空间群为P21。基于密度泛函计算和群论分析，最近有人提出NaLaMnWO_6应该是具有相对较大极化（16 μC cm（-2））的铁电体。与这一预测相反，我们的电学测量，如传统的P-E环，正向上和负向下（PUND），压电响应和二次谐波产生（SHG）揭示了NaLnMnWO 6（Ln = La，Nd，Tb）的铁电极化的存在。一个介电异常观察到低于室温（270 K）的所有三种化合物，这是有关的电导率的变化所揭示的温度依赖性的交流和直流电阻率。在相同温度下也观察到了热释电流峰。然而，它的起源不能归因于铁电转变。
The ordered perovskites, NaLnMnWO6 (Ln = La, Nd, Tb), are reported to exhibit simultaneous ordering of A-site cations (Na and Ln) in layered arrangement and B-site cations (Mn and W) in rock salt structure. They have been shown to crystallize in a monoclinic structure with the polar space group P21. Based on density functional calculations and group theoretical analysis, it has recently been proposed that NaLaMnWO6 should be ferroelectric with a relatively large polarization (16 μC cm(-2)). Contrary to this prediction, our electrical measurements such as conventional P-E loop, Positive-Up and Negative-Down (PUND), piezoelectric response and Second Harmonic Generation (SHG) reveal the absence of ferroelectric polarization in NaLnMnWO6 (Ln = La, Nd, Tb). A dielectric anomaly is observed just below room temperature (∼270 K) for all the three compounds, which is related to the change in conductivity as revealed by temperature dependent ac and dc resistivity. A pyrocurrent peak is also observed at the same temperature. However, its origin cannot be attributed to a ferroelectric transition.