The origin of ferroelectricity in Hf1-xZrxO2: A computational investigation and a surface energy model
The origin of ferroelectricity in Hf1-xZrxO2: A computational investigation and a surface energy model
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DOI：
10.1063/1.4916707
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发表时间：
2015-04-07
影响因子：
3.2
通讯作者：
Kersch, A.
中科院分区：
文献类型：
--
作者：
Materlik, R.;Kuenneth, C.;Kersch, A.
研究了HfO 2、ZrO 2和Hf-0.5Zr0.5O2（HZO）铁电相的结构、热和介电性质，并通过密度泛函计算进行了验证。我们发现，在Hf 1-xZrxO 2体系中，正交晶系Pca 2（1）相的自由体能比单斜晶系P2（1）/c和正交晶系Pbca相的自由体能要小.为了解释纳米薄膜中铁电相的存在，我们探索吉布斯/亥姆霍兹自由能作为应力和薄膜应变的函数，并发现它们不太可能成为最小的HZO薄膜的技术相关条件。为了评估表面能的贡献的相稳定性，我们parameterising模型，现有的数据之间的插值，并找到最小的尺寸和化学计量的范围内的铁电晶粒的亥姆霍兹自由能。从该模型中，我们预测未掺杂的HfO 2是铁电的晶粒尺寸约为4 nm和外延HZO低于5 nm。此外，我们还计算了使ZrO_2从P_4（2）/nmc相转变为反铁电相所需的外加电场强度为1 MV/cm，这与实验数据相符，解释了场致相变的机理。(C)2015 AIP Publishing LLC.
The structural, thermal, and dielectric properties of the ferroelectric phase of HfO2, ZrO2, and Hf-0.5Zr0.5O2 (HZO) are investigated with carefully validated density functional computations. We find that the free bulk energy of the ferroelectric orthorhombic Pca2(1) phase is unfavorable compared to the monoclinic P2(1)/c and the orthorhombic Pbca phase for all investigated stoichiometries in the Hf1-xZrxO2 system. To explain the existence of the ferroelectric phase in nanoscale thin films, we explore the Gibbs/Helmholtz free energies as a function of stress and film strain and find them unlikely to become minimal in HZO films for technological relevant conditions. To assess the contribution of surface energy to the phase stability, we parameterize a model, interpolating between existing data, and find the Helmholtz free energy of ferroelectric grains minimal for a range of size and stoichiometry. From the model, we predict undoped HfO2 to be ferroelectric for a grain size of about 4 nm and epitaxial HZO below 5 nm. Furthermore, we calculate the strength of an applied electric field necessary to cause the antiferroelectric phase transformation in ZrO2 from the P4(2)/nmc phase as 1 MV/cm in agreement with experimental data, explaining the mechanism of field induced phase transformation. (C) 2015 AIP Publishing LLC.