BaTiO3/BaO超晶格中竞争铁电和反铁电不稳定性的第一性原理研究
First-principles study of competing ferroelectric and antiferroelectric instabilities in BaTiO3/BaO superlattices
摘要：
我们报道了（BaTiO ${_3}$）$_m$ /（BaO）$_n$超晶格的第一性原理研究，研究了周期性$m/n$的变化.我们发现，这样的系统开发一个极性区中心不稳定性足够大的\textit{m} / \textit{n}比，这可以理解，至少定性地说，从一个简单的静电模型，并应导致铁电基态。然而，声子色散曲线的分析也指出，出现在$m=4$周围的区域边界处的反铁电不稳定性较强，达到铁电性的临界比之前，仍然占主导地位超过它。该分析使我们能够预测，（BaTiO ${_3}$）$_m$ /（BaO）$_n$超晶格应该呈现反铁电基态的$m$大于4，这应该顺利地演变为多畴结构的增加$m$值，只有成为大$m$的铁电。
英文摘要：
We report a first-principles study of (BaTiO${_3}$)$_m$/(BaO)$_n$ superlattices for a wide range of periodicities $m/n$. We show that such a system develops a polar zone-center instability for sufficiently large \textit{m}/\textit{n} ratio, which can be understood, at least qualitatively, from a simple electrostatic model and should lead to a ferroelectric ground-state. However, the analysis of the phonon dispersion curves also points out the appearance of stronger antiferroelectric instabilities at the zone boundaries around $m=4$, before the critical ratio for ferroelectricity is reached and which still dominate beyond it. The dominant character of the anti-ferroelectric instability is explained from the depolarizing field which hardens the ferroelectric mode. This analysis allows us to predict that, (BaTiO${_3}$)$_m$/(BaO)$_n$ superlattices should present an antiferroelectric ground state for $m$ larger than 4, which should smoothly evolve to a multidomain structure for increasing $m$ values and only become ferroelectric for large $m$.
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