Influence of oxygen vacancies on the dielectric properties of hafnia : First-principles calculations
Influence of oxygen vacancies on the dielectric properties of hafnia : First-principles calculations
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DOI：
10.1103/physrevb.75.094103
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发表时间：
2007-03
影响因子：
3.7
通讯作者：
E. Cockayne
中科院分区：
文献类型：
--
作者：
E. Cockayne
采用第一性原理计算方法研究了中性空位和带2+电荷的氧空位对晶体$\ mathm {Hf}{\ mathm {O}}_{2}$介电性能的影响。中性空位在四倍配位位点更稳定，而带电空位在三倍配位位点更稳定。对于两个空位，$\mathrm{Hf}{\mathrm{O}}_{2}$保持绝缘，无论空位是中性的还是处于$2+$电荷状态。计算了每种结构的动力学矩阵、玻恩有效电荷和电子介电张量。当每64个氧原子中有一个氧空位时，中性空位的静态介电常数${\ensuremath{\kappa}}_{s}$增加了1% ~ 2%，而$2+$带电空位的静态介电常数${{s}$被抑制了1% ~ 3%，其中三层配位空位的变化更大。带电空位的确切结果取决于如何对宏观电荷中性所必需的中和电荷进行建模。中性氧空位${\ensuremath{\kappa}}_{s}$的增加是由于电子介电响应的增强，这是由于一对电子占据了容易极化的$F$中心缺陷态。${\ensuremath{\kappa}}_{s}$中带电氧空位的抑制是由于声子硬化，这降低了离子响应。没有证据表明氧空位诱导的特征性局域声子可以通过红外或拉曼光谱检测到。
First-principles calculations were used to study the effects of neutral and $2+$ charged oxygen vacancies on the dielectric properties of crystalline $\mathrm{Hf}{\mathrm{O}}_{2}$. In agreement with previous results, the neutral vacancy is more stable on four fold-coordinated site, while the charged vacancy is more stable on a three fold-coordinated site. For both vacancy positions, $\mathrm{Hf}{\mathrm{O}}_{2}$ remains insulating whether the vacancy is neutral or in the $2+$ charge state. The dynamical matrix, Born effective charges, and electronic dielectric tensor were calculated for each structure. With one oxygen vacancy per 64 oxygen atoms, the static dielectric constant ${\ensuremath{\kappa}}_{s}$ is increased by 1%--2% for neutral vacancies and suppressed by 1%--3% for $2+$ charged vacancies, with the larger changes for three fold-coordinated vacancies. The exact result in the case of a charged vacancy depends on how the neutralizing charge necessary for macroscopic charge neutrality is modeled. The increase in ${\ensuremath{\kappa}}_{s}$ for neutral oxygen vacancies arises from an enhancement of the electronic dielectric response due to a pair of electrons occupying an easily polarizable $F$-center defect state. The suppression in ${\ensuremath{\kappa}}_{s}$ for charged oxygen vacancies is due to phonon hardening, which reduces the ionic response. No evidence is found for characteristic localized phonons induced by oxygen vacancies that could be detected by infrared or Raman spectroscopy.