Abstract A hierarchical NiO-[CdO]2 nanocomposite has been synthesized by a sol–gel auto-combustion route and characterized with a view to studying the electric field emission and conduction mechanism therein. The structural features, surface morphologies, and elemental compositions of the as-prepared samples have been characterized by XRD, Raman, FESEM, and TEM techniques. A low turn-on field (4.50 V/μm) and threshold field (5.04 V/μm) were found to be sufficient to draw emission current densities of 1 μA/cm2 and 10 μA/cm2 from NiO-[CdO]2-modified cathodes. A maximum emission current density of 121 μA/cm2 at a low applied electric field of 6.5 V/μm and long emission current stability were achieved at a preset value of 5 μA. The field enhancement factor (β) was determined as 1854 in the high-field region by computing the local work function (φ) through density functional theory (DFT), and the entire field emission (FE) performances have been compared with those of various pristine compounds. The temperature-dependent electrical conduction mechanism has been further explained with the help of impedance analysis over the temperature range 323–623 K and a wide frequency range from 5 Hz to 1 MHz. The grain and grain boundary contributions were well distinguished by impedance and a modulus formalism, with respective activation energies of Eg = 0.25–0.26 eV and Egb = 0.31–0.32 eV. The temperature-dependent frequency exponents for grains (n1) and grain boundaries (n2) demonstrate two different conduction mechanisms, namely quantum mechanical tunneling for grains, and correlated barrier hopping for grain boundaries. Maxwell–Wagner-type dielectric polarizations are explained by our experimental results, and the highest real dielectric constant (er) 1893 was calculated at 623 K.

中文翻译：

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NiO-[CdO]2 纳米复合材料中晶粒和晶界的优异场发射和交流传导机制

摘要 为了研究其中的电场发射和传导机制，通过溶胶-凝胶自燃路线合成了分层 NiO-[CdO]2 纳米复合材料并对其进行表征。所制备样品的结构特征、表面形貌和元素组成已通过 XRD、拉曼、FESEM 和 TEM 技术进行表征。发现低开启场 (4.50 V/μm) 和阈值场 (5.04 V/μm) 足以从 NiO-[CdO]2 改性中提取 1 μA/cm2 和 10 μA/cm2 的发射电流密度阴极。在 6.5 V/μm 的低外加电场下，最大发射电流密度为 121 μA/cm2，并且在预设值 5 μA 下实现了长发射电流稳定性。通过密度泛函理论（DFT）计算局部功函数（φ），确定高场区域的场增强因子（β）为1854，并与各种不同的场发射（FE）性能进行了比较。原始化合物。借助阻抗分析在 323-623 K 温度范围和 5 Hz 至 1 MHz 的宽频率范围内进一步解释了与温度相关的导电机制。通过阻抗和模量形式可以很好地区分晶粒和晶界的贡献，各自的活化能为 Eg = 0.25-0.26 eV 和 Egb = 0.31-0.32 eV。晶粒 (n1) 和晶界 (n2) 的温度相关频率指数证明了两种不同的传导机制，即晶粒的量子力学隧道效应，和相关的晶界跳跃障碍。Maxwell-Wagner 型介电极化由​​我们的实验结果解释，最高实际介电常数 (er) 1893 计算为 623 K。