Nathalie Lemée

Bismuth sodium titanate (BNT) thin films were deposited on Pt/SiN substrates by Sol-Gel spin coating technique and annealed under O₂ atmosphere. The microstructural, structural, and electrical properties of the obtained film were investigated. Electron microscopy scans and atomic force microscopy micrographs were used to analyze the microstructure of the films. Furthermore, energy-dispersive X-ray spectroscopy (EDX) analysis revealed a Na-deficient composition for the obtained film. X-ray diffraction and Raman spectroscopy allowed the identification of a pure perovskite BNT phase. Dielectric, ferroelectric, and leakage current measurements revealed good frequency stability of the dielectric constant and dielectric losses for BNT thin film. The results are discussed in terms of Na deficiency effects on the defect structure of BNT. Further, the film showed attractive electrostatic energy storage properties with energy density that exceeds 1.04 J/cm³ under E = 630 kV/cm.

Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNT-BT) thin films were prepared via both chemical solution (CSD) and pulsed laser deposition (PLD). The structural, dielectric, and ferroelectric properties were investigated. High stability of the dielectric permittivity or TCC (∆ε/ε (150 °C) ≤ ±15%) over a wide temperature range from room temperature to 300 °C was obtained. Distinctly, the CSD film showed high TCC stability with variation of ±5% up to 250 °C. Furthermore, the CSD film showed an unsaturated ferroelectric hysteresis loop characteristic of the ergodic relaxor phase. However, the PLD one exhibited an almost saturated loop characteristic of the coexistence of both ergodic and non-ergodic states. The energy storage properties of the prepared films were determined using P–E loops obtained at different temperatures. The results show that these films exhibited a stable and improved energy storage density comparable to ceramic capacitors. Moreover, the CSD film exhibited more rigidity and better energy storage density, which exceeded 1.3 J/cm³ under a weak applied field of 317 kV/cm, as well as interesting efficiency in a large temperature range. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Bismuth sodium titanate thin films (BNT) were deposited on Pt/SiN substrates by Sol-Gel spin coating technique under O2 atmosphere. Microstructural, structural, and electrical properties of the obtained film were investigated. Scanning electron microscopy and atomic force microscopy micrographs were used to analyze the microstructure of the films. Furthermore, EDX analysis revealed a Na-deficient composition for the obtained film. X-ray diffraction and Raman spectroscopy allowed the identification of a pure perovskite BNT phase. Dielectric, ferroelectric, and leakage current measurements revealed good frequency stability of the dielectric constant and dielectric losses for BNT thin film. The results are discussed in terms of Na-deficiency effects on the defect structure of BNT. Further, the film showed attractive electrostatic energy storage properties with energy density that exceeds 1.04 J/cm3 under E = 630 kV/cm.

Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-BT) thin films were prepared by both chemical solution (CSD) and pulsed laser deposition (PLD). The microstructure, dielectric, and ferroelectric properties were investigated. High stability of the dielectric permittivity (∆ɛ/ɛ(150 °C) ≤ ± 15%) over a wide temperature range from room temperature to 300 °C was obtained. Distinctly, the CSD film showed high TCC stability with variation of ± 5% up to 250°C. Furthermore, the CSD film showed an unsaturated ferroelectric hysteresis loop characteristic of the ergodic relaxor phase, however the PLD one exhibited almost saturated loop signature of the coexistence of both ergodic and non-ergodic states. The energy storage properties of the prepared films were determined using the P–E loops obtained at different temperatures. The results showed that these films exhibit stable and improved energy storage density comparable to the ceramic capacitors. Moreover, the CSD film exhibited more rigidity and better energy storage density that exceeds 1.3 J/cm3 under low applied field of 317 KV/cm as well as interesting efficiency in a large temperature range. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Rare earth element-doped Bi_0.5Na_0.5TiO₃–BaTiO₃ (BNT–BT–RE) polycrystalline thin films were processed on a platinized substrate by chemical solution deposition. The microstructure, dielectric, and ferroelectric properties were investigated for all prepared films. It was found that the incorporation of rare earth elements into the BNT–BT matrix increases both the dielectric constant and the breakdown strength while maintaining low dielectric losses, leading to an enhancement of the energy storage density to W_rec = 12 and 16 J/cm³ under an effective field of E = 2500 kV/cm, for Nd- and Dy-based films, respectively. The optical properties of films containing the lanthanide element were investigated and the obtained results bear interest for luminescence applications. The simultaneous appearance of ferroelectric and optical properties in the system under investigation is very promising for advanced optoelectronic devices.

A comprehensive theoretical study of the structure, electronic, optical, and elastic properties of ternary semiconductor silver thiogallate crystal AgGaS₂ is carried out based on the density functional theory and dipole electron shifting model (DES) for finding a structure–properties relationship. The deformation and displacement parameters, describing the deviation of the structural parameters of AgGaS₂ from ideal chalcopyrite structure, are determined. It is noticed that the significant discrepancies concerning peculiarities of the band structure between initial results of the DFT‐based calculation and the experiment for the titled crystal have been efficiently eliminated by choosing the proper DFT + U approach. By utilizing the calculated dielectric function for two principal directions, the refractive indices and extinction coefficients dispersions are determined. For the first time, the linear electro‐optic properties, electrogyration coefficients, and second‐order nonlinear optical coefficients of AgGaS₂ crystals are calculated in the frame of the DES model. The elastic properties of the AgGaS crystal are analyzed in the frame of the calculated full matrix of elastic coefficients. A number of parameters, such as Young's modulus E, Poisson's ratio ν, bulk B, and shear G moduli are predicted for the crystal. The calculated anisotropy coefficients for the moduli show very good agreement with ones available from experiment.

Hydrogenated nanocrystalline silicon, while being non-charged and non-polar, could be an ideal candidate for the non-covalent and orientation-controlled immobilization of biomolecules thanks to local electric fields around nanocrystals. To that effect, the adsorption of bovine serum albumin on substrates with different densities of nanocrystals, revealed by Raman spectroscopy and X-ray diffraction, was studied using infrared spectroscopy and atomic force microscopy. It was found that the protein–surface interactions followed different mechanisms depending on the nanostructure at the surface: hydrophobic on the non-crystalline part of the surface and electrostatic around the crystalline part. These electrostatic interactions were driven by the electric fields that arose at the junction between crystalline and amorphous structures. These electric fields were found to be strong enough to interact with the amide dipoles, thereby reorienting the adsorbed protein molecules on this part of the surface. Nevertheless, the adsorbed proteins were found to be denatured, which was due to the surface chemistry, and not affected by the nanostructure.