Electrochemical impedance spectroscopy analysis of hydrogen-doped perovskite nickel oxide materials

The rare-earth perovskite nickel oxides (RNiO₃) are a subgroup of perovskite oxides which are actively investigated in the research fields related to electronics and photonics. This is because the RNiO₃ materials can be used toward various energy-efficient applications such as neuromorphic chips, Mott transistors, optical sensors, or fuel cells. All RNiO₃ materials, excluding the LaNiO₃, show a common characteristic of metal-to-insulator transition (MIT) at a specific temperature, in which such MIT temperature differs depending on different rare-earth elements (R from RNiO₃) used. As a result, the RNiO₃ materials show an insulating behavior below the MIT temperature, and a metallic behavior above the MIT temperature. In this thesis, the neodymium nickel oxide (NdNiO₃) is developed as a thin film grown on a LaAlO₃ crystal substrate using the spin-coating method of the chemical solution deposition (CSD) technique. The metallic behavior of NdNiO₃ is observed by the current-voltage (I-V) measurement, and its crystalline state is determined using X-ray diffraction (XRD). The palladium (Pd) electrodes are fabricated on the NdNiO₃ thin film using the electron-beam deposition, and a hydrogen doping process is performed for the H-NdNiO₃ structure. After the hydrogen doping process, the H-NdNiO₃ are primarily formed at the surrounding regions of the Pd electrodes. The electrochemical impedance spectroscopy (EIS) measurement is performed on the hydrogen-doped NdNiO₃ thin film in order to observe the conductivity mechanism of H-NdNiO₃ and NdNiO₃ at different frequencies. The EIS measurements are performed at multiple temperatures to determine its temperature-driven conductivity effect as well. The result of the EIS measurements shows the conductivity mechanism from the H-NdNiO₃ region. The real impedance (Z') and the negative imaginary impedance (− Z") values are determined at different angular frequencies (ω), which are used to determine the behavior of the AC conductivity with respect to the angular frequencies (ω). The rapid increase of the AC conductivity of the H-NdNiO₃ is observed at high angular frequencies. The activation energy and the DC conductivity values (σDC) from Jonscher’s power law are determined to investigate the proton conduction mechanism of H-NdNiO₃ from the EIS measurement.