Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol–gel/spin-coating approach of polycrystalline LiNbO₃ films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol–gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO₃ films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films.

This paper presents a simple and optimized metal organic chemical vapor deposition (MOCVD) protocol for the deposition of perovskite BiFeO₃ films on silicon-based substrates, in order to move toward the next generation of lead-free hybrid energy harvesters. A bi-metal mixture that is composed of Bi(phenyl)₃, and Fe(tmhd)₃ has been used as a precursor source. BiFeO₃ films have been grown by MOCVD on IrO₂/Si substrates, in which the conductive IrO₂ functions as a bottom electrode and a buffer layer. BiFeO₃ films have been analyzed by X-ray diffraction (XRD) for structural characterization and by field-emission scanning electron microscopy (FE-SEM) coupled with energy dispersive X-ray (EDX) analysis for the morphological and chemical characterizations, respectively. These studies have shown that the deposited films are polycrystalline, pure BiFeO₃ phase highly homogenous in morphology and composition all over the entire substrate surface. Piezoelectric force microscopy (PFM) and Piezoelectric Force Spectroscopy (PFS) checked the piezoelectric and ferroelectric properties of the film.

Epitaxial thin films of lithium niobate with a thickness of 160 nm, oriented along the crystallographic c axis, were grown by direct liquid injection chemical vapor deposition on c-sapphire substrates. Different families of very high-frequency surface acoustic waves with general polarization exist in such piezoelectric films on high-velocity substrates. Surface Brillouin light scattering measurements, complemented with fast finite element analysis of wave dispersion, demonstrate Rayleigh, leaky shear, and leaky longitudinal surface waves, excited at frequencies between 10 and 30 GHz. The Brillouin technique reveals dispersion and anisotropy of propagation without the implementation of high-frequency surface acoustic wave transducers.

CoFeB alloy is a ferromagnetic material that is often considered to produce synthetic antiferromagnets (SAF) used in spintronic devices. SAF host spin waves with high tunability, making their coupling with surface acoustic waves (SAWs) a promising avenue for next-generation communication devices. This coupling offers potential advantages such as SAW tunability and non-reciprocal operation in the multi-gigahertz range. Epitaxial lithium niobate (LN) thin films on sapphire substrates have emerged as a promising solution for achieving high SAW phase velocities. The combination of LN thin films with SAF, for instance based on CoFeB-based multilayers, hence offers new possibilities for engineering acoustic wave propagation. As the elastic properties of CoFeB depend on the composition of the alloy, their determination is a requisite to evaluate SAW dispersion. We investigate elastic wave dispersion in Co₄₀Fe₄₀B₂₀-based multilayers on LN/ZX-sapphire, ZX-LN, and SiO₂/Si substrates, combining surface Brillouin light spectroscopy and finite element computations. Surface-guided phonons ranging from 9 to 18 GHz are observed, for a wavelength of about 300 nm, and the elastic constants of Co₄₀Fe₄₀B₂₀ are estimated from them.

The temperature dependence of the elastic constants C11E, C12E, C14E, and C44E as well as the piezoelectrically stiffened constants C13D and C33D of lithium niobate (LN) was determined using polarized Brillouin light scattering. The congruent (48.38 mol. % of Li2O) and nearly stoichiometric (49.5 mol. %) compositions of LN were studied from room temperature up to 800 and 900 °C, respectively. Brillouin measurements were taken on X-, Y-, Z-, and (YXl)/45° LN cuts using temperature-resolved refractive index data and corrected for density variations. At room temperature, the measured elastic constants of congruent LN are generally in agreement with the values previously reported in the literature. Variations of C11E, C12E, C13D, and C33D with temperature are observed to be approximately linear up to 800 °C. In contrast, shear elastic constants C14E and C44E exhibit a strong nonlinear behavior above 400 °C. This coincides with an inversion in the thermal expansion of the c axis lattice parameter. The thermal activation of a shear optical phonon mode, which is estimated to be at 14 THz, may explain these structural and mechanical changes while preserving the trigonal structure. This change is decorrelated from the second-order phase transition driven by spontaneous polarization near the Curie temperature.