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Ferroelectric fatigue in layered perovskites from self-energy corrected density functional theory

机译：基于自能校正密度泛函理论的层状钙钛矿中的铁电疲劳

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We employed self-energy corrected density functional theory (GGA-1/2) to investigate the band alignment between platinum and the layered perovskite Aurivillius ferroelectrics SrBi2Ta2O9 (SBT), Bi4Ti3O12 (BIT), and La-substituted BIT (BLT). The original GGA-1/2 method was found to not give satisfactory band gaps for these layered materials, despite yielding substantially better band gaps than GGA. We show that in such layered materials the cutoff radius for the self-energy potential in GGA-1/2 is strongly inhomogeneous across layers, therefore requiring different cutoff radii assigned to oxygen anions located in bismuth oxide layers and in pseudo-perovskite layers. After a 2D optimization of the oxygen cutoff radii, the calculated band gaps for these materials were found within 0.3?eV of experimental values. Next, we developed stoichiometric interface models for Pt/SBT and Pt/BIT, assuming platinum was connected to bismuth oxide layers as suggested by experiments. The calculated Schottky (hole) barriers for abrupt interfaces are 1.58 eV (2.50 eV) and 2.06 eV (1.41 eV) for SBT and BIT, respectively. For Pt(Bi) alloyed interfaces, where according to experiments some Bi diffuses inside the metal, we calculated a downshift of the Fermi level, lowering the barrier for holes. Because the barrier height for holes is lower in Pt/BIT than in Pt/SBT, a higher space-charge-limited-conduction hole current is expected to leak through metal alloyed Pt(Bi)/BIT/Pt(Bi) capacitors than to the corresponding SBT capacitors. Finally, replacing some Bi in the pseudo-perovskite layers with La significantly increased the barrier for holes. Based on the results above, we propose a phenomenological model for ferroelectric fatigue in Pt/BIT/Pt, whereby the formation of a non-ferroelectric Bi-deficient phase is the main reason for fatigue, which is accelerated by the lowered barrier for holes promoting the accumulation of Bi vacancies. The fatigue-free nature of Pt/SBT/Pt and Pt/BLT/Pt, on the other hand, stems from large barriers for both electrons and holes, which prevent the neutralization and further accumulation of charged defects. Our conclusions are consistent with the available experimental data.
机译：我们采用自能量校正密度泛函理论（GGA-1 / 2）研究了铂与层状钙钛矿铁氧体铁电体SrBi 2 Ta < sub> 2 O 9 （SBT），Bi 4 Ti 3 O 12 （BIT）和La取代的BIT（BLT）。发现原始的GGA-1 / 2方法不能为这些层状材料提供令人满意的带隙，尽管产生的带隙比GGA好得多。我们表明，在这种层状材料中，GGA-1 / 2中自能势的截止半径在各层之间强烈不均匀，因此需要分配给位于氧化铋层和拟钙钛矿层中的氧阴离子的不同截止半径。对氧气截止半径进行二维优化后，发现这些材料的计算带隙在实验值的0.3？eV以内。接下来，我们假设实验所建议的铂与氧化铋层相连，我们开发了Pt / SBT和Pt / BIT的化学计量界面模型。对于SBT和BIT，计算得出的突变界面的肖特基（空穴）势垒分别为1.58 eV（2.50 eV）和2.06 eV（1.41 eV）。对于Pt（Bi）合金界面，根据实验，一些Bi在金属内部扩散，我们计算了费米能级的下移，从而降低了空穴的势垒。由于Pt / BIT中的空穴势垒高度低于Pt / SBT中的空穴势垒高度，因此，期望通过金属合金化Pt（Bi）/ BIT / Pt（Bi）电容器泄漏的电流会更大，从而限制了空间电荷限制导电空穴电流的泄漏。相应的SBT电容器。最后，用La代替准钙钛矿层中的某些Bi会大大增加空穴的阻挡层。基于以上结果，我们提出了Pt / BIT / Pt中铁电疲劳的现象学模型，其中非铁电Bi缺陷相的形成是疲劳的主要原因，这是由于降低了促进空穴的势垒而加速的。碧空缺的积累。另一方面，Pt / SBT / Pt和Pt / BLT / Pt的无疲劳性质源于电子和空穴的大势垒，阻止了电荷缺陷的中和和进一步积累。我们的结论与现有的实验数据一致。

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