论文标题
镁氧化镁中铁电的起源
Origin of ferroelectricity in magnesium doped zinc oxide
论文作者
论文摘要
最近的实验表明，Wurtzite结构的MG掺杂ZnO（ZMO）中有强大的铁电性，暗示了一种有希望的策略，可以通过掺杂常规的压电来实质性地扩大铁电的清单。我们使用第一原理密度功能理论（DFT）研究了ZMO中铁电性的起源。 MG合金可以软化ZMO的离子势能表面进行极化反转的一般论点过于简化。我们的DFT计算表明，即使在高毫克浓度下，当应变固定在极相上时，极性和非极相之间的能量差（$ΔU$）对于ZMO系统而言仍然很大。有趣的是，当允许应变弛豫时，$ΔU$的大小会大大较小，接近典型的钙钛矿铁电去的价值，例如pbtio $ _3 $，随着MG掺杂浓度的增加。 ZMO系统的启用切换性归因于MGO的六角形相比其Wurtzite对应物低得多。详细的轨道和键合分析支持，原子内$ 3D_ {z^2} $ - $ 4P_Z $轨道的Zn的轨道自我混合在稳定极地Wurtzite相中起着重要作用，缺乏造成MGO的低功能非光相的非光相的非光相的责任。
Recent experiments demonstrated robust ferroelectricity in Mg-doped ZnO (ZMO) of the wurtzite structure, hinting at a promising strategy to substantially expand the list of ferroelectrics by doping conventional piezoelectrics. We investigate the origin of ferroelectricity in ZMO with first-principles density functional theory (DFT). The general argument that the Mg alloying could soften the ionic potential energy surface of ZMO for polarization reversal is overly simplified. Our DFT calculations reveal that even at a high Mg concentration, the energy difference ($ΔU$) between the polar and nonpolar phases remains prohibitively large for ZMO systems when the strain is fixed to the polar phase. Interestingly, the magnitude of $ΔU$ becomes substantially smaller when the strain relaxation is allowed, approaching the value of typical perovskite ferroelectrics such as PbTiO$_3$ with increasing Mg doping concentrations. The enabled switchability of ZMO systems is attributed to a hexagonal phase of MgO that is much lower in energy than its wurtzite counterpart. Detailed orbital and bonding analysis supports that the intra-atomic $3d_{z^2}$-$4p_z$ orbital self-mixing of Zn plays an important role in stabilizing the polar wurtzite phase, the lack of which is responsible for the low-energy nonpolar hexagonal phase of MgO.
