arXiv subjects

Pierre-Marie Geffroy

Publications and source records attributed to Pierre-Marie Geffroy.

3 recordsLinked to original sources

arXiv2026

Impact of sintering conditions on the dielectric properties of TiO2 ceramics for metamaterialsapplications at terahertz frequencies

Titanium dioxyde (TiO2) is a promising dielectric material for the realization of metamaterials operating in the terahertz (THz) range. Indeed, these necessitate a high permittivity and low loss material. In this paper, we compare the processes of fabrication and the results of characterisation of bulk TiO2 pellets. From the results of this characterization, we have numerically designed 2D all dielectric metamaterials (ADM) showing that they may exhibit negative or near-zero effective index. Our previous simulations show that the relative permittivity epsilon has to be around 100, while the loss tangent has to be lower than 0.02. We have thus compared conventional sintering (CS) vs spark plasma sintering (SPS), and investigated the effect of post-sintering annealing on the loss to satisfy these two criteria. The samples were characterized by THz Time Domain Spectroscopy (THz-TDS). One of the samples exhibits a loss tangent as low as 0.006, with a permittivity epsilon = 103. These results highlight the importance of the fabrication process on the EM properties of bulk TiO2, and demonstrate that it is a promising material for the development of metamaterial in the THz band.

cond-mat.mtrl-sci↗

arXiv2025

Atomic scale structure and dynamical properties of (TeO$_2$)$_{1-x}$-(Na$_2$O)$_{x}$ glasses through first-principles modeling and XRD measurements

We resort to first-principles molecular dynamics, in synergy with experiments, to study structural evolution and Na$^+$ cation diffusion inside (TeO$_2$)$_{1-x}$-(Na$_2$O)$_{x}$ (x = 0.10-0.40) glasses. Experimental and modeling results show a fair quantitative agreement in terms of total X-ray structure factors and pair distribution functions, thereby setting the ground for a comprehensive analysis of the glassy matrix evolution. We find that the structure of (TeO$_2$)$_{1-x}$-(Na$_2$O)$_{x}$ glasses deviates drastically from that of pure TeO$_2$ glass. Specifically, increasing the Na$_2$O concentration leads to a reduction of the coordination number of Te atoms, reflecting the occurrence of a structural depolymerization upon introduction of the Na$_2$O modifier oxide. The depolymerization phenomenon is ascribed to the transformation of Te-O-Te bridges into terminal Te-O non bridging oxygen atoms (NBO). Consequently, the concentration of NBO increases in these systems as the concentration of the modifier increases, accompanied by a concomitant reduction in the coordination number of Na atoms. The structure factors results show a prominent peak at 1.4 A, that becomes more and more pronounced as the Na2O concentration increases. The occurrence of this first sharp diffraction peak is attributed to the growth of Na-rich channels inside the amorphous network, acting as preferential routes for alkali-ion conduction inside the relatively stable Te-O matrix. These channels enhance the ion mobility.

cond-mat.mtrl-sci↗

arXiv2017

High permittivity processed SrTiO3 for metamaterials applications at terahertz frequencies

High permittivity SrTiO3 for the realization of all-dielectric metamaterials operating at terahertz frequencies was fabricated. A comparison of different processing routes evidences that Spark Plasma Sintering is the most effective sintering process to yield high density ceramic with high permittivity. We compare this sintering process with two others. The elaborated samples are characterized in the low frequency and in the terahertz frequency ranges. Their relative permittivities are compared with that a reference \sto single crystal. The permittivity of the sample elaborated by Spark Plasma Sintering is as high as that the single crystal.

physics.app-ph↗