Fadhel El Kamel

This study investigates the dielectric relaxation and electrical conduction mechanisms in Au/ a ‐(Ba _2/3 ,Sr _1/3 )TiO ₃ (850 nm)/Pt structures across a wide temperature range. A high relative permittivity of 100 was measured. Analysis of Arrhenius plots reveals two distinct relaxation processes and multiple conduction regimes. At low temperatures, a first relaxation and bulk conductivity coexist with a common activation energy of 0.50 eV, attributed to the thermally activated reorientation of polar defect complexes. A second relaxation emerges, marked by a significant decrease in activation energy from 0.87 to 0.56 eV at 210°C. Combined with the observation of depressed Nyquist arcs and broadened tanδ(ω) peaks, this transition provides quantitative evidence for the formation and cooperative diffusion of oxygen vacancy clusters. Above 160°C, the bulk conduction arises from the thermally activated hopping of free charge carriers between trapping sites (Ti ⁴⁺ in reduced TiO ₆ octahedra) by overcoming an energetic barrier of 1.16 eV. The interfacial conduction is thermally activated with an energy that varies from 1.75 to 0.64 eV when the temperature exceeds 275°C. It is expected that this mechanism is ascribed to the catalytic activity identified at the BST/Pt interface and to the electronic detrapping from oxygen vacancies, respectively. These results highlight that the complex interplay between structural disorder, vacancy clustering, and catalytic activity of the electrode is governing the functional performance of amorphous titanate‐based capacitors.

BaTiO3:H Films as All-Solid-State Electrolytes for Integrated Electric Double-Layer Capacitors | InTechOpen, Published on: 2016-11-02. Authors: Fadhel El Kamel

Dielectric as well as thermally stimulated current measurements were performed on metal/HfO₂/Pt capacitors in order to study the electrical active defects in hafnia thin films. Two thermally activated relaxation processes have been carried out from both measurements. At low temperatures, the relaxation process can be ascribed to the shallow traps level localized at 0.65 eV and generally evidenced by the second ionization of oxygen vacancies. At high temperatures, the relaxation process arises from the diffusion of positively charged oxygen vacancies by overcoming an energetic barrier of about 1 eV.

Electrical measurements are realized on Cu/HfO ₂ /Pt capacitors to extract the electron effective mass in HfO ₂ and the barrier height at the Cu/HfO ₂ interface. The dominant conduction mechanisms are found to be the Schottky emission at medium voltages and the Fowler–Nordheim tunneling at high voltages. Previous research has usually been carried out by assuming a constant value for either the electron effective mass in oxide or the interfacial potential barrier height to determine the other parameter. However, in contrast to that general practice, an iterative method was proposed in the present study to determine, at the same time, the electron effective mass in HfO ₂ and the barrier height at the Cu/HfO ₂ interface without making any prior assumption about their values. The temperature dependence of these two parameters was also studied in the 298–423 K range. It is found that they strongly vary with temperature. The effective mass decreases quadratically with temperature, while the barrier height increases linearly with temperature.

Hydrogenated barium titanate films show enhancement of the double-layer capacitance and therefore can be employed as electrolytes in the all-solid-state supercapacitors. This behavior was attributed to the accumulation of protons at the metal–electrolyte interface over a Debye length (capacitive double layer). Electrical measurements were carried out on hydrogenated layers (BaTiO3:H) and trilayer stack (BaTiO3/BaTiO3:H/BaTiO3) to study the active defects at the origin of the conduction mechanisms.