电子阴极系统中$Sc_2O_3$的本征缺陷与导电特性
Intrinsic defects and conduction characteristics of $Sc_2O_3$ in thermionic cathode systems
摘要：
最近的实验观察表明，体$Sc_2O_3$（~200 nm厚），在室温和压力下的绝缘体，必须作为一个良好的电子导体在电子阴极操作，导致观察到的高发射电流密度和整体优于传统的电子发射器，不包含$Sc_2O_3$的发射性能。在这里，我们采用从头算方法，使用半局域和混合泛函计算的本征缺陷能量的Sc和O的空位和晶体及其对$Sc_2O_3$的电子性质的影响，试图解释在实验中观察到的良好的导电$Sc_2O_3$。在平衡缺陷模型中使用缺陷能量学来计算平衡时的缺陷浓度及其补偿电子和空穴浓度。总体而言，我们的结果表明，$Sc_2O_3$的电导率仅仅由于在阴极操作环境中的固有缺陷的存在下是不可能足够高，以保持从实验中获得的发射电流密度的大小，并且杂质的存在是必要的，以提高$Sc_2O_3$的电导率到足够高的值，以解释在实验中观察到的电流密度。赋予足够的电子传导所需的最小杂质浓度非常小（约为$7.5x10^{-3}$ ppm），并且可能存在于所有实验中。
英文摘要：
Recent experimental observations indicate that bulk $Sc_2O_3$ (~200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain $Sc_2O_3$. Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of $Sc_2O_3$ in an effort to explain the good conduction of $Sc_2O_3$ observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of $Sc_2O_3$ solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that presence of impurities are necessary to raise the conductivity of $Sc_2O_3$ to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately $7.5x10^{-3}$ ppm) and is probably present in all experiments.
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