npj Computational Materials

Unexpectedly large energy variations from dopant interactions in ferroelectric HfO2from high-throughput ab initio calculations （高通量从头算预测HfO2铁电体掺杂剂相互作用的意外特大能量变化）
Max Falkowski, Christopher Künneth, Robin Materlik & Alfred Kersch
npj Computational Materials 4:73 (2018)
doi:s41524-018-0133-4
Published online:10 December 2018
Abstract| Full Text | PDF OPEN

摘要:了解过程相关属性（如小规模不均匀性）的起源是材料优化的关键。本研究使用DFT计算分析了随机掺杂Si、La和VO对HfO2结构的影响，并将其与生产过程相联系。用粗粒度方法比较了在局部不均匀性的影响下，相关铁电Pbc21相的总能与竞争的晶体相总能进行了比较。掺杂剂之间的相互作用增加了掺杂剂随机定位的统计效应。在原子层或化学溶液沉积后的退火过程中，由于掺杂剂不会扩散，与陶瓷工艺回火相比，原子层或化学溶液沉积后的退火过程相对较短，但仍然存在较大的能量变化。由于能量差异是相稳定性的判据，这种大的变化表明存在纳米区和弥散相变的可能性，因为这些局部掺杂效应可能使系统在顺电-铁电相界上来回移动。　　

Abstract:Insight into the origin of process-related properties like small-scale inhomogeneities is key for material optimization. Here, we analyze DFT calculations of randomly doped HfO2 structures with Si, La, and VO and relate them to the kind of production process. Total energies of the relevant ferroelectric Pbc21 phase are compared with the competing crystallographic phases under the influence of the arising local inhomogeneities in a coarse-grained approach. The interaction among dopants adds to the statistical effect from the random positioning of the dopants. In anneals after atomic layer or chemical solution deposition processes, which are short compared to ceramic process tempering, the large energy variations remain because the dopants do not diffuse. Since the energy difference is the criterion for the phase stability, the large variation suggests the possibility of nanoregions and diffuse phase transitions because these local doping effects may move the system over the paraelectric-ferroelectric phase boundary.

Editorial Summary

Ferroelectrics: Dopant interactions stabilize nanoscale phases （铁电体：掺杂剂之间的相互作用稳定纳米级相）

该研究对掺杂的HfO2进行了大尺度的密度泛函理论计算，并发现掺杂剂-掺杂剂之间的相互作用可以稳定纳米相。来自德国慕尼黑应用科学大学的Max Falkowski、Alfred Kersch和他们的同事对HfO2使用La或/和Si进行掺杂，其超结构具有1纳米的尺寸，他们对这些结构进行了高通量DFT计算。他们发现掺杂剂之间的相互作用范围在1 nm范围内，这与铁电相相对于介电相的稳定性有关。由于掺杂剂的相互作用，计算出的各结构相之间的能量变化出乎意料地大。结果表明，在这种材料中形成了纳米金属氧化物和纳米分子效应，这对于理解新近的实验发现非常重要，例如居里温度变宽、相间边界和弥散相变等。

Large-scale density functional theory calculations (DFT) are performed on doped HfO2 where the dopant-dopant interactions are found to stabilize nanoscale phases. Max Falkowski, Alfred Kersch and co-workers from the Munich University of Applied Sciences in Germany carried out high-throughput DFT calculations with 1-nm-sized supercells of La or/and Si-doped HfO2. They found that the range of dopant interactions is on the scale of 1-nm, which is relevant for the stability of the ferroelectric phase relative to the dielectric phase. The calculated energy variation among all relevant phases is unexpectedly large, caused by the dopant interaction. The results suggest formation of nanoregions and nanolaminate effects in this material, which is important to understand recent experimental findings, such as Curie temperature broadening, interphase boundaries, and diffuse phase transitions.